AI Trajectory

null

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "bpf_binprm_set_interp",
    "search_binfmt_handler",
    "get_binfmt_handler",
    "load_misc_binary",
    "create_entry",
    "bm_register_write"
  ],
  "Reasoning": "The patch introduces a new 'B' (BPF) handler type for binfmt_misc, allowing BPF programs to match binaries and select interpreters. This adds new reachable core logic in binfmt_misc registration and binary execution paths, as well as a new BPF helper function.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 56fb40b431fb554ecc4a1a2858062819f4f56c48\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Sat Jul 4 21:31:14 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c\nindex 84349fcb93f13a..cf6698d59c9f04 100644\n--- a/fs/binfmt_misc.c\n+++ b/fs/binfmt_misc.c\n@@ -29,6 +29,11 @@\n #include \u003clinux/fs.h\u003e\n #include \u003clinux/uaccess.h\u003e\n \n+#ifdef CONFIG_BPF_SYSCALL\n+#include \u003clinux/bpf.h\u003e\n+#include \u003clinux/filter.h\u003e\n+#endif\n+\n #include \"internal.h\"\n \n #ifdef DEBUG\n@@ -41,12 +46,14 @@ enum {\n \tVERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */\n };\n \n-enum {Enabled, Magic};\n+enum {Enabled, Magic, Bpf};\n #define MISC_FMT_PRESERVE_ARGV0 (1UL \u003c\u003c 31)\n #define MISC_FMT_OPEN_BINARY (1UL \u003c\u003c 30)\n #define MISC_FMT_CREDENTIALS (1UL \u003c\u003c 29)\n #define MISC_FMT_OPEN_FILE (1UL \u003c\u003c 28)\n \n+struct bpf_prog;\n+\n typedef struct {\n \tstruct list_head list;\n \tunsigned long flags;\t\t/* type, status, etc. */\n@@ -59,6 +66,9 @@ typedef struct {\n \tstruct dentry *dentry;\n \tstruct file *interp_file;\n \trefcount_t users;\t\t/* sync removal with load_misc_binary() */\n+#ifdef CONFIG_BPF_SYSCALL\n+\tstruct bpf_prog *bpf_prog;\n+#endif\n } Node;\n \n static struct file_system_type bm_fs_type;\n@@ -78,10 +88,51 @@ static struct file_system_type bm_fs_type;\n  */\n #define MAX_REGISTER_LENGTH 1920\n \n+#ifdef CONFIG_BPF_SYSCALL\n+struct binfmt_bpf_interp {\n+\tchar path[PATH_MAX];\n+\tint len;\t/* \u003c 0 if the current program set no interpreter */\n+};\n+static DEFINE_PER_CPU(struct binfmt_bpf_interp, binfmt_bpf_interp);\n+\n+/*\n+ * bpf_binprm_set_interp - let a binfmt_misc 'B' program pick the interpreter.\n+ * @path: interpreter path, in BPF-accessible memory\n+ * @len:  number of bytes in @path\n+ *\n+ * The program computes the interpreter path however it sees fit (e.g. relative\n+ * to the binary). The path is stashed on a per-CPU area that binfmt_misc reads\n+ * back immediately after running the program under migrate_disable(), so it\n+ * cannot race with another CPU.\n+ */\n+BPF_CALL_2(bpf_binprm_set_interp, const char *, path, u32, len)\n+{\n+\tstruct binfmt_bpf_interp *sc = this_cpu_ptr(\u0026binfmt_bpf_interp);\n+\n+\tif (len == 0 || len \u003e= PATH_MAX)\n+\t\treturn -EINVAL;\n+\t/* @path is @len bytes of BPF memory and is not NUL-terminated. */\n+\tmemcpy(sc-\u003epath, path, len);\n+\tsc-\u003epath[len] = '\\0';\n+\tsc-\u003elen = len;\n+\treturn 0;\n+}\n+\n+const struct bpf_func_proto bpf_binprm_set_interp_proto = {\n+\t.func\t\t= bpf_binprm_set_interp,\n+\t.gpl_only\t= false,\n+\t.ret_type\t= RET_INTEGER,\n+\t.arg1_type\t= ARG_PTR_TO_MEM | MEM_RDONLY,\n+\t.arg2_type\t= ARG_CONST_SIZE,\n+};\n+#endif /* CONFIG_BPF_SYSCALL */\n+\n /**\n  * search_binfmt_handler - search for a binary handler for @bprm\n  * @misc: handle to binfmt_misc instance\n  * @bprm: binary for which we are looking for a handler\n+ * @bpf_interp: receives a kmalloc'd interpreter path if a 'B' program chooses\n+ *              one via bpf_binprm_set_interp(); the caller must kfree() it\n  *\n  * Search for a binary type handler for @bprm in the list of registered binary\n  * type handlers.\n@@ -89,7 +140,8 @@ static struct file_system_type bm_fs_type;\n  * Return: binary type list entry on success, NULL on failure\n  */\n static Node *search_binfmt_handler(struct binfmt_misc *misc,\n-\t\t\t\t   struct linux_binprm *bprm)\n+\t\t\t\t   struct linux_binprm *bprm,\n+\t\t\t\t   char **bpf_interp)\n {\n \tchar *p = strrchr(bprm-\u003einterp, '.');\n \tNode *e;\n@@ -103,6 +155,37 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,\n \t\tif (!test_bit(Enabled, \u0026e-\u003eflags))\n \t\t\tcontinue;\n \n+\t\t/* Do matching based on BPF if applicable. */\n+\t\tif (test_bit(Bpf, \u0026e-\u003eflags)) {\n+#ifdef CONFIG_BPF_SYSCALL\n+\t\t\tif (e-\u003ebpf_prog) {\n+\t\t\t\tstruct binfmt_bpf_interp *sc;\n+\t\t\t\tu32 ret;\n+\n+\t\t\t\tmigrate_disable();\n+\t\t\t\tsc = this_cpu_ptr(\u0026binfmt_bpf_interp);\n+\t\t\t\tsc-\u003elen = -1;\n+\n+\t\t\t\trcu_read_lock();\n+\t\t\t\tret = bpf_prog_run(e-\u003ebpf_prog, bprm-\u003ebuf);\n+\t\t\t\trcu_read_unlock();\n+\n+\t\t\t\tif (ret == 1 \u0026\u0026 sc-\u003elen \u003e 0)\n+\t\t\t\t\t*bpf_interp = kmemdup_nul(sc-\u003epath,\n+\t\t\t\t\t\t\t\t  sc-\u003elen,\n+\t\t\t\t\t\t\t\t  GFP_ATOMIC);\n+\t\t\t\tmigrate_enable();\n+\n+\t\t\t\tpr_debug(\"binfmt_misc: ran BPF program for %s, ret = %u\\n\",\n+\t\t\t\t\t bprm-\u003efilename, ret);\n+\n+\t\t\t\tif (ret == 1)\n+\t\t\t\t\treturn e;\n+\t\t\t}\n+#endif\n+\t\t\tcontinue;\n+\t\t}\n+\n \t\t/* Do matching based on extension if applicable. */\n \t\tif (!test_bit(Magic, \u0026e-\u003eflags)) {\n \t\t\tif (p \u0026\u0026 !strcmp(e-\u003emagic, p + 1))\n@@ -139,12 +222,13 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,\n  * Return: binary type list entry on success, NULL on failure\n  */\n static Node *get_binfmt_handler(struct binfmt_misc *misc,\n-\t\t\t\tstruct linux_binprm *bprm)\n+\t\t\t\tstruct linux_binprm *bprm,\n+\t\t\t\tchar **bpf_interp)\n {\n \tNode *e;\n \n \tread_lock(\u0026misc-\u003eentries_lock);\n-\te = search_binfmt_handler(misc, bprm);\n+\te = search_binfmt_handler(misc, bprm, bpf_interp);\n \tif (e)\n \t\trefcount_inc(\u0026e-\u003eusers);\n \tread_unlock(\u0026misc-\u003eentries_lock);\n@@ -164,6 +248,10 @@ static void put_binfmt_handler(Node *e)\n \tif (refcount_dec_and_test(\u0026e-\u003eusers)) {\n \t\tif (e-\u003eflags \u0026 MISC_FMT_OPEN_FILE)\n \t\t\tfilp_close(e-\u003einterp_file, NULL);\n+#ifdef CONFIG_BPF_SYSCALL\n+\t\tif (test_bit(Bpf, \u0026e-\u003eflags) \u0026\u0026 e-\u003ebpf_prog)\n+\t\t\tbpf_prog_put(e-\u003ebpf_prog);\n+#endif\n \t\tkfree(e);\n \t}\n }\n@@ -206,15 +294,27 @@ static int load_misc_binary(struct linux_binprm *bprm)\n \tstruct file *interp_file = NULL;\n \tint retval = -ENOEXEC;\n \tstruct binfmt_misc *misc;\n+\tchar *bpf_interp __free(kfree) = NULL;\n+\tconst char *interpreter;\n \n \tmisc = load_binfmt_misc();\n \tif (!misc-\u003eenabled)\n \t\treturn retval;\n \n-\tfmt = get_binfmt_handler(misc, bprm);\n+\tfmt = get_binfmt_handler(misc, bprm, \u0026bpf_interp);\n \tif (!fmt)\n \t\treturn retval;\n \n+\t/*\n+\t * A 'B' (BPF) handler carries no interpreter of its own; the program\n+\t * chooses it via bpf_binprm_set_interp(). Other handlers use the\n+\t * interpreter recorded at registration.\n+\t */\n+\tinterpreter = bpf_interp ? bpf_interp : fmt-\u003einterpreter;\n+\tretval = -ENOEXEC;\n+\tif (!interpreter[0])\n+\t\tgoto ret;\n+\n \t/* Need to be able to load the file after exec */\n \tretval = -ENOENT;\n \tif (bprm-\u003einterp_flags \u0026 BINPRM_FLAGS_PATH_INACCESSIBLE)\n@@ -238,22 +338,27 @@ static int load_misc_binary(struct linux_binprm *bprm)\n \tbprm-\u003eargc++;\n \n \t/* add the interp as argv[0] */\n-\tretval = copy_string_kernel(fmt-\u003einterpreter, bprm);\n+\tretval = copy_string_kernel(interpreter, bprm);\n \tif (retval \u003c 0)\n \t\tgoto ret;\n \tbprm-\u003eargc++;\n \n \t/* Update interp in case binfmt_script needs it. */\n-\tretval = bprm_change_interp(fmt-\u003einterpreter, bprm);\n+\tretval = bprm_change_interp(interpreter, bprm);\n \tif (retval \u003c 0)\n \t\tgoto ret;\n \n-\tif (fmt-\u003eflags \u0026 MISC_FMT_OPEN_FILE) {\n+\t/*\n+\t * The pre-opened interp_file (MISC_FMT_OPEN_FILE / 'F' flag) only\n+\t * applies to the statically registered interpreter; a program-supplied\n+\t * path is opened here.\n+\t */\n+\tif ((fmt-\u003eflags \u0026 MISC_FMT_OPEN_FILE) \u0026\u0026 !bpf_interp) {\n \t\tinterp_file = file_clone_open(fmt-\u003einterp_file);\n \t\tif (!IS_ERR(interp_file))\n \t\t\tdeny_write_access(interp_file);\n \t} else {\n-\t\tinterp_file = open_exec(fmt-\u003einterpreter);\n+\t\tinterp_file = open_exec(interpreter);\n \t}\n \tretval = PTR_ERR(interp_file);\n \tif (IS_ERR(interp_file))\n@@ -404,6 +509,10 @@ static Node *create_entry(const char __user *buffer, size_t count)\n \t\tpr_debug(\"register: type: M (magic)\\n\");\n \t\te-\u003eflags = (1 \u003c\u003c Enabled) | (1 \u003c\u003c Magic);\n \t\tbreak;\n+\tcase 'B':\n+\t\tpr_debug(\"register: type: B (bpf)\\n\");\n+\t\te-\u003eflags = (1 \u003c\u003c Enabled) | (1 \u003c\u003c Bpf);\n+\t\tbreak;\n \tdefault:\n \t\tgoto einval;\n \t}\n@@ -492,6 +601,45 @@ static Node *create_entry(const char __user *buffer, size_t count)\n \t\t\t\t}\n \t\t\t}\n \t\t}\n+\t} else if (test_bit(Bpf, \u0026e-\u003eflags)) {\n+\t\t/* Handle the 'B' (BPF) format. */\n+\t\tchar *s;\n+\n+\t\t/* The offset field actually holds the pinned BPF program path */\n+\t\ts = strchr(p, del);\n+\t\tif (!s)\n+\t\t\tgoto einval;\n+\t\t*s++ = '\\0';\n+\t\te-\u003emagic = p; /* Keep path in e-\u003emagic */\n+\t\tpr_debug(\"register: bpf program path: %s\\n\", e-\u003emagic);\n+\n+#ifdef CONFIG_BPF_SYSCALL\n+\t\te-\u003ebpf_prog = bpf_prog_get_type_path(e-\u003emagic, BPF_PROG_TYPE_SOCKET_FILTER);\n+\t\tif (IS_ERR(e-\u003ebpf_prog)) {\n+\t\t\terr = PTR_ERR(e-\u003ebpf_prog);\n+\t\t\te-\u003ebpf_prog = NULL;\n+\t\t\tkfree(e);\n+\t\t\treturn ERR_PTR(err);\n+\t\t}\n+#else\n+\t\tgoto einval;\n+#endif\n+\n+\t\tp = s;\n+\n+\t\t/* The magic field is unused, must be empty */\n+\t\ts = strchr(p, del);\n+\t\tif (!s || p != s)\n+\t\t\tgoto einval;\n+\t\t*s++ = '\\0';\n+\t\tp = s;\n+\n+\t\t/* The mask field is unused, must be empty */\n+\t\ts = strchr(p, del);\n+\t\tif (!s || p != s)\n+\t\t\tgoto einval;\n+\t\t*s++ = '\\0';\n+\t\tp = s;\n \t} else {\n \t\t/* Handle the 'E' (extension) format. */\n \n@@ -524,8 +672,17 @@ static Node *create_entry(const char __user *buffer, size_t count)\n \tif (!p)\n \t\tgoto einval;\n \t*p++ = '\\0';\n-\tif (!e-\u003einterpreter[0])\n+\tif (test_bit(Bpf, \u0026e-\u003eflags)) {\n+\t\t/*\n+\t\t * A 'B' (BPF) handler carries no interpreter of its own; the\n+\t\t * program picks it via bpf_binprm_set_interp(). Reject a\n+\t\t * statically registered one.\n+\t\t */\n+\t\tif (e-\u003einterpreter[0])\n+\t\t\tgoto einval;\n+\t} else if (!e-\u003einterpreter[0]) {\n \t\tgoto einval;\n+\t}\n \tpr_debug(\"register: interpreter: {%s}\\n\", e-\u003einterpreter);\n \n \t/* Parse the 'flags' field. */\n@@ -602,7 +759,9 @@ static void entry_status(Node *e, char *page)\n \t\t*dp++ = 'F';\n \t*dp++ = '\\n';\n \n-\tif (!test_bit(Magic, \u0026e-\u003eflags)) {\n+\tif (test_bit(Bpf, \u0026e-\u003eflags)) {\n+\t\tsprintf(dp, \"bpf %s\\n\", e-\u003emagic);\n+\t} else if (!test_bit(Magic, \u0026e-\u003eflags)) {\n \t\tsprintf(dp, \"extension .%s\\n\", e-\u003emagic);\n \t} else {\n \t\tdp += sprintf(dp, \"offset %i\\nmagic \", e-\u003eoffset);\ndiff --git a/include/linux/bpf.h b/include/linux/bpf.h\nindex 7719f652844560..3aef44b694bd0a 100644\n--- a/include/linux/bpf.h\n+++ b/include/linux/bpf.h\n@@ -3874,6 +3874,7 @@ extern const struct bpf_func_proto bpf_ktime_get_ns_proto;\n extern const struct bpf_func_proto bpf_ktime_get_boot_ns_proto;\n extern const struct bpf_func_proto bpf_ktime_get_tai_ns_proto;\n extern const struct bpf_func_proto bpf_get_current_pid_tgid_proto;\n+extern const struct bpf_func_proto bpf_binprm_set_interp_proto;\n extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;\n extern const struct bpf_func_proto bpf_get_current_comm_proto;\n extern const struct bpf_func_proto bpf_get_stackid_proto;\ndiff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h\nindex 89b36de5fdbb6d..dce155c5bbd75e 100644\n--- a/include/uapi/linux/bpf.h\n+++ b/include/uapi/linux/bpf.h\n@@ -6142,6 +6142,7 @@ union bpf_attr {\n \tFN(user_ringbuf_drain, 209, ##ctx)\t\t\\\n \tFN(cgrp_storage_get, 210, ##ctx)\t\t\\\n \tFN(cgrp_storage_delete, 211, ##ctx)\t\t\\\n+\tFN(binprm_set_interp, 212, ##ctx)\t\t\\\n \t/* This helper list is effectively frozen. If you are trying to\t\\\n \t * add a new helper, you should add a kfunc instead which has\t\\\n \t * less stability guarantees. See Documentation/bpf/kfuncs.rst\t\\\ndiff --git a/net/core/filter.c b/net/core/filter.c\nindex 2e96b4b847ce12..187692a4a4b67b 100644\n--- a/net/core/filter.c\n+++ b/net/core/filter.c\n@@ -8397,6 +8397,14 @@ sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)\n \t\treturn \u0026bpf_get_socket_uid_proto;\n \tcase BPF_FUNC_perf_event_output:\n \t\treturn \u0026bpf_skb_event_output_proto;\n+#if IS_BUILTIN(CONFIG_BINFMT_MISC)\n+\tcase BPF_FUNC_binprm_set_interp:\n+\t\t/*\n+\t\t * binfmt_misc reuses SOCKET_FILTER programs to select an\n+\t\t * interpreter; expose the helper that lets them set it.\n+\t\t */\n+\t\treturn \u0026bpf_binprm_set_interp_proto;\n+#endif\n \tdefault:\n \t\treturn bpf_sk_base_func_proto(func_id, prog);\n \t}\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "bpf_binprm_set_interp",
    "search_binfmt_handler",
    "get_binfmt_handler",
    "load_misc_binary",
    "create_entry",
    "bm_register_write"
  ],
  "Reasoning": "The patch introduces a new 'B' (BPF) handler type for binfmt_misc, allowing BPF programs to match binaries and select interpreters. This adds new reachable core logic in binfmt_misc registration and binary execution paths, as well as a new BPF helper function.",
  "WorthFuzzing": true
}

You are an expert Linux kernel maintainer.
Your job is to review a provided patch series and determine
if it makes functional changes to the kernel that should be fuzzed.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on your internal knowledge of the kernel. You must actively
use your code access tools to examine the actual source code and confirm any assumptions.

Return WorthFuzzing=false if the patch only contains:
- Modifications to Documentation/, Kconfig files, or code comments.
- Purely decorative changes, such as logging (e.g., pr_err, printk) or tracepoints.
- Changes to numeric constants or macros that do not functionally alter execution flow.
- Code paths that are impossible to reach in virtualized environments like GCE or QEMU,
even when utilizing software-emulated hardware (e.g., usb gadget, mac80211_hwsim).

If it modifies reachable core kernel logic, drivers, or architectures, use your code search
tools to verify the code can be executed, then return WorthFuzzing=true.

When returning WorthFuzzing=true, you MUST ALSO:
1. Extract any specific kernel functions that should be heavily fuzzed into FocusSymbols.
   Avoid listing generic hot-path functions to prevent skewed test distributions.
2. Identify any specific CONFIG_ options required to properly test this new/modified feature.
   Go and look into the Kconfig files and check for ifdefs around the code, do not make assumptions.
   Do not list too generic configs (we already have them enabled). Only list those that
   specifically cover the modified code. List them in the EnableConfigs output array,
   and DO NOT add a 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

For your convenience, here is the diff of the changes:
commit 56fb40b431fb554ecc4a1a2858062819f4f56c48
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Jul 4 21:31:14 2026 +0000

    syz-cluster: applied patch under review

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 84349fcb93f13a..cf6698d59c9f04 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -29,6 +29,11 @@
 #include <linux/fs.h>
 #include <linux/uaccess.h>
 
+#ifdef CONFIG_BPF_SYSCALL
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#endif
+
 #include "internal.h"
 
 #ifdef DEBUG
@@ -41,12 +46,14 @@ enum {
 	VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
 };
 
-enum {Enabled, Magic};
+enum {Enabled, Magic, Bpf};
 #define MISC_FMT_PRESERVE_ARGV0 (1UL << 31)
 #define MISC_FMT_OPEN_BINARY (1UL << 30)
 #define MISC_FMT_CREDENTIALS (1UL << 29)
 #define MISC_FMT_OPEN_FILE (1UL << 28)
 
+struct bpf_prog;
+
 typedef struct {
 	struct list_head list;
 	unsigned long flags;		/* type, status, etc. */
@@ -59,6 +66,9 @@ typedef struct {
 	struct dentry *dentry;
 	struct file *interp_file;
 	refcount_t users;		/* sync removal with load_misc_binary() */
+#ifdef CONFIG_BPF_SYSCALL
+	struct bpf_prog *bpf_prog;
+#endif
 } Node;
 
 static struct file_system_type bm_fs_type;
@@ -78,10 +88,51 @@ static struct file_system_type bm_fs_type;
  */
 #define MAX_REGISTER_LENGTH 1920
 
+#ifdef CONFIG_BPF_SYSCALL
+struct binfmt_bpf_interp {
+	char path[PATH_MAX];
+	int len;	/* < 0 if the current program set no interpreter */
+};
+static DEFINE_PER_CPU(struct binfmt_bpf_interp, binfmt_bpf_interp);
+
+/*
+ * bpf_binprm_set_interp - let a binfmt_misc 'B' program pick the interpreter.
+ * @path: interpreter path, in BPF-accessible memory
+ * @len:  number of bytes in @path
+ *
+ * The program computes the interpreter path however it sees fit (e.g. relative
+ * to the binary). The path is stashed on a per-CPU area that binfmt_misc reads
+ * back immediately after running the program under migrate_disable(), so it
+ * cannot race with another CPU.
+ */
+BPF_CALL_2(bpf_binprm_set_interp, const char *, path, u32, len)
+{
+	struct binfmt_bpf_interp *sc = this_cpu_ptr(&binfmt_bpf_interp);
+
+	if (len == 0 || len >= PATH_MAX)
+		return -EINVAL;
+	/* @path is @len bytes of BPF memory and is not NUL-terminated. */
+	memcpy(sc->path, path, len);
+	sc->path[len] = '\0';
+	sc->len = len;
+	return 0;
+}
+
+const struct bpf_func_proto bpf_binprm_set_interp_proto = {
+	.func		= bpf_binprm_set_interp,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_MEM | MEM_RDONLY,
+	.arg2_type	= ARG_CONST_SIZE,
+};
+#endif /* CONFIG_BPF_SYSCALL */
+
 /**
  * search_binfmt_handler - search for a binary handler for @bprm
  * @misc: handle to binfmt_misc instance
  * @bprm: binary for which we are looking for a handler
+ * @bpf_interp: receives a kmalloc'd interpreter path if a 'B' program chooses
+ *              one via bpf_binprm_set_interp(); the caller must kfree() it
  *
  * Search for a binary type handler for @bprm in the list of registered binary
  * type handlers.
@@ -89,7 +140,8 @@ static struct file_system_type bm_fs_type;
  * Return: binary type list entry on success, NULL on failure
  */
 static Node *search_binfmt_handler(struct binfmt_misc *misc,
-				   struct linux_binprm *bprm)
+				   struct linux_binprm *bprm,
+				   char **bpf_interp)
 {
 	char *p = strrchr(bprm->interp, '.');
 	Node *e;
@@ -103,6 +155,37 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,
 		if (!test_bit(Enabled, &e->flags))
 			continue;
 
+		/* Do matching based on BPF if applicable. */
+		if (test_bit(Bpf, &e->flags)) {
+#ifdef CONFIG_BPF_SYSCALL
+			if (e->bpf_prog) {
+				struct binfmt_bpf_interp *sc;
+				u32 ret;
+
+				migrate_disable();
+				sc = this_cpu_ptr(&binfmt_bpf_interp);
+				sc->len = -1;
+
+				rcu_read_lock();
+				ret = bpf_prog_run(e->bpf_prog, bprm->buf);
+				rcu_read_unlock();
+
+				if (ret == 1 && sc->len > 0)
+					*bpf_interp = kmemdup_nul(sc->path,
+								  sc->len,
+								  GFP_ATOMIC);
+				migrate_enable();
+
+				pr_debug("binfmt_misc: ran BPF program for %s, ret = %u\n",
+					 bprm->filename, ret);
+
+				if (ret == 1)
+					return e;
+			}
+#endif
+			continue;
+		}
+
 		/* Do matching based on extension if applicable. */
 		if (!test_bit(Magic, &e->flags)) {
 			if (p && !strcmp(e->magic, p + 1))
@@ -139,12 +222,13 @@ static Node *search_binfmt_handler(struct binfmt_misc *misc,
  * Return: binary type list entry on success, NULL on failure
  */
 static Node *get_binfmt_handler(struct binfmt_misc *misc,
-				struct linux_binprm *bprm)
+				struct linux_binprm *bprm,
+				char **bpf_interp)
 {
 	Node *e;
 
 	read_lock(&misc->entries_lock);
-	e = search_binfmt_handler(misc, bprm);
+	e = search_binfmt_handler(misc, bprm, bpf_interp);
 	if (e)
 		refcount_inc(&e->users);
 	read_unlock(&misc->entries_lock);
@@ -164,6 +248,10 @@ static void put_binfmt_handler(Node *e)
 	if (refcount_dec_and_test(&e->users)) {
 		if (e->flags & MISC_FMT_OPEN_FILE)
 			filp_close(e->interp_file, NULL);
+#ifdef CONFIG_BPF_SYSCALL
+		if (test_bit(Bpf, &e->flags) && e->bpf_prog)
+			bpf_prog_put(e->bpf_prog);
+#endif
 		kfree(e);
 	}
 }
@@ -206,15 +294,27 @@ static int load_misc_binary(struct linux_binprm *bprm)
 	struct file *interp_file = NULL;
 	int retval = -ENOEXEC;
 	struct binfmt_misc *misc;
+	char *bpf_interp __free(kfree) = NULL;
+	const char *interpreter;
 
 	misc = load_binfmt_misc();
 	if (!misc->enabled)
 		return retval;
 
-	fmt = get_binfmt_handler(misc, bprm);
+	fmt = get_binfmt_handler(misc, bprm, &bpf_interp);
 	if (!fmt)
 		return retval;
 
+	/*
+	 * A 'B' (BPF) handler carries no interpreter of its own; the program
+	 * chooses it via bpf_binprm_set_interp(). Other handlers use the
+	 * interpreter recorded at registration.
+	 */
+	interpreter = bpf_interp ? bpf_interp : fmt->interpreter;
+	retval = -ENOEXEC;
+	if (!interpreter[0])
+		goto ret;
+
 	/* Need to be able to load the file after exec */
 	retval = -ENOENT;
 	if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
@@ -238,22 +338,27 @@ static int load_misc_binary(struct linux_binprm *bprm)
 	bprm->argc++;
 
 	/* add the interp as argv[0] */
-	retval = copy_string_kernel(fmt->interpreter, bprm);
+	retval = copy_string_kernel(interpreter, bprm);
 	if (retval < 0)
 		goto ret;
 	bprm->argc++;
 
 	/* Update interp in case binfmt_script needs it. */
-	retval = bprm_change_interp(fmt->interpreter, bprm);
+	retval = bprm_change_interp(interpreter, bprm);
 	if (retval < 0)
 		goto ret;
 
-	if (fmt->flags & MISC_FMT_OPEN_FILE) {
+	/*
+	 * The pre-opened interp_file (MISC_FMT_OPEN_FILE / 'F' flag) only
+	 * applies to the statically registered interpreter; a program-supplied
+	 * path is opened here.
+	 */
+	if ((fmt->flags & MISC_FMT_OPEN_FILE) && !bpf_interp) {
 		interp_file = file_clone_open(fmt->interp_file);
 		if (!IS_ERR(interp_file))
 			deny_write_access(interp_file);
 	} else {
-		interp_file = open_exec(fmt->interpreter);
+		interp_file = open_exec(interpreter);
 	}
 	retval = PTR_ERR(interp_file);
 	if (IS_ERR(interp_file))
@@ -404,6 +509,10 @@ static Node *create_entry(const char __user *buffer, size_t count)
 		pr_debug("register: type: M (magic)\n");
 		e->flags = (1 << Enabled) | (1 << Magic);
 		break;
+	case 'B':
+		pr_debug("register: type: B (bpf)\n");
+		e->flags = (1 << Enabled) | (1 << Bpf);
+		break;
 	default:
 		goto einval;
 	}
@@ -492,6 +601,45 @@ static Node *create_entry(const char __user *buffer, size_t count)
 				}
 			}
 		}
+	} else if (test_bit(Bpf, &e->flags)) {
+		/* Handle the 'B' (BPF) format. */
+		char *s;
+
+		/* The offset field actually holds the pinned BPF program path */
+		s = strchr(p, del);
+		if (!s)
+			goto einval;
+		*s++ = '\0';
+		e->magic = p; /* Keep path in e->magic */
+		pr_debug("register: bpf program path: %s\n", e->magic);
+
+#ifdef CONFIG_BPF_SYSCALL
+		e->bpf_prog = bpf_prog_get_type_path(e->magic, BPF_PROG_TYPE_SOCKET_FILTER);
+		if (IS_ERR(e->bpf_prog)) {
+			err = PTR_ERR(e->bpf_prog);
+			e->bpf_prog = NULL;
+			kfree(e);
+			return ERR_PTR(err);
+		}
+#else
+		goto einval;
+#endif
+
+		p = s;
+
+		/* The magic field is unused, must be empty */
+		s = strchr(p, del);
+		if (!s || p != s)
+			goto einval;
+		*s++ = '\0';
+		p = s;
+
+		/* The mask field is unused, must be empty */
+		s = strchr(p, del);
+		if (!s || p != s)
+			goto einval;
+		*s++ = '\0';
+		p = s;
 	} else {
 		/* Handle the 'E' (extension) format. */
 
@@ -524,8 +672,17 @@ static Node *create_entry(const char __user *buffer, size_t count)
 	if (!p)
 		goto einval;
 	*p++ = '\0';
-	if (!e->interpreter[0])
+	if (test_bit(Bpf, &e->flags)) {
+		/*
+		 * A 'B' (BPF) handler carries no interpreter of its own; the
+		 * program picks it via bpf_binprm_set_interp(). Reject a
+		 * statically registered one.
+		 */
+		if (e->interpreter[0])
+			goto einval;
+	} else if (!e->interpreter[0]) {
 		goto einval;
+	}
 	pr_debug("register: interpreter: {%s}\n", e->interpreter);
 
 	/* Parse the 'flags' field. */
@@ -602,7 +759,9 @@ static void entry_status(Node *e, char *page)
 		*dp++ = 'F';
 	*dp++ = '\n';
 
-	if (!test_bit(Magic, &e->flags)) {
+	if (test_bit(Bpf, &e->flags)) {
+		sprintf(dp, "bpf %s\n", e->magic);
+	} else if (!test_bit(Magic, &e->flags)) {
 		sprintf(dp, "extension .%s\n", e->magic);
 	} else {
 		dp += sprintf(dp, "offset %i\nmagic ", e->offset);
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 7719f652844560..3aef44b694bd0a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3874,6 +3874,7 @@ extern const struct bpf_func_proto bpf_ktime_get_ns_proto;
 extern const struct bpf_func_proto bpf_ktime_get_boot_ns_proto;
 extern const struct bpf_func_proto bpf_ktime_get_tai_ns_proto;
 extern const struct bpf_func_proto bpf_get_current_pid_tgid_proto;
+extern const struct bpf_func_proto bpf_binprm_set_interp_proto;
 extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;
 extern const struct bpf_func_proto bpf_get_current_comm_proto;
 extern const struct bpf_func_proto bpf_get_stackid_proto;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 89b36de5fdbb6d..dce155c5bbd75e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6142,6 +6142,7 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(binprm_set_interp, 212, ##ctx)		\
 	/* This helper list is effectively frozen. If you are trying to	\
 	 * add a new helper, you should add a kfunc instead which has	\
 	 * less stability guarantees. See Documentation/bpf/kfuncs.rst	\
diff --git a/net/core/filter.c b/net/core/filter.c
index 2e96b4b847ce12..187692a4a4b67b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8397,6 +8397,14 @@ sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_get_socket_uid_proto;
 	case BPF_FUNC_perf_event_output:
 		return &bpf_skb_event_output_proto;
+#if IS_BUILTIN(CONFIG_BINFMT_MISC)
+	case BPF_FUNC_binprm_set_interp:
+		/*
+		 * binfmt_misc reuses SOCKET_FILTER programs to select an
+		 * interpreter; expose the helper that lets them set it.
+		 */
+		return &bpf_binprm_set_interp_proto;
+#endif
 	default:
 		return bpf_sk_base_func_proto(func_id, prog);
 	}

gemini-3.1-pro-preview

null

null

							input: 6300
							output: 28
							thoughts: 229
						

**Analyzing the BPF binfmt_misc Patch**

Okay, so I'm looking at this patch that introduces a new binfmt_misc handler type, 'B' – for BPF, naturally. The idea is to use a BPF program to dynamically select an interpreter based on the binary itself. Seems like a clever approach for enhanced flexibility. This patch is touching `fs/binfmt_misc.c`, which is a key area for managing executable formats, as expected.

I see they've added a new BPF helper, `bpf_binprm_set_interp`, which is central to this whole thing. Plus, modifications to crucial functions like `search_binfmt_handler`, `get_binfmt_handler`, `load_misc_binary`, `create_entry`, and `entry_status`, indicate they've integrated this BPF-based approach deeply into the existing binfmt_misc infrastructure. Now, I need to understand the configuration dependencies.

The core code is guarded by `#ifdef CONFIG_BPF_SYSCALL` within `fs/binfmt_misc.c`, which makes sense; this assumes the BPF syscalls are available. `CONFIG_BINFMT_MISC` is, of course, the main configuration option here. Let me see if there are other, related configurations at play. Aha, I see `IS_BUILTIN(CONFIG_BINFMT_MISC)` used in `net/core/filter.c` which could be an interesting point of convergence.

Time to broaden the search for dependencies. I'll fire up `grepper` to see if there are any other configuration variables or other interactions I've overlooked. I need to make sure I grasp the full scope of this change before I form any judgements about its potential impacts or integration challenges.

{
  "Expression": "CONFIG_BINFMT_MISC",
  "PathPrefix": ""
}

{
  "Output": "Documentation/admin-guide/java.rst=8=other program after you have done the following:\n--\nDocumentation/admin-guide/java.rst-21-2) You have to compile BINFMT_MISC either as a module or into\nDocumentation/admin-guide/java.rst:22:   the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.\nDocumentation/admin-guide/java.rst-23-   If you choose to compile it as a module, you will have\n--\nDocumentation/admin-guide/mono.rst=9=other program after you have done the following:\n--\nDocumentation/admin-guide/mono.rst-25-2) You have to compile BINFMT_MISC either as a module or into\nDocumentation/admin-guide/mono.rst:26:   the kernel (``CONFIG_BINFMT_MISC``) and set it up properly.\nDocumentation/admin-guide/mono.rst-27-   If you choose to compile it as a module, you will have\n--\narch/arm/configs/axm55xx_defconfig=50=CONFIG_MODULE_UNLOAD=y\narch/arm/configs/axm55xx_defconfig-51-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/arm/configs/axm55xx_defconfig:52:CONFIG_BINFMT_MISC=y\narch/arm/configs/axm55xx_defconfig-53-# CONFIG_COMPAT_BRK is not set\n--\narch/arm/configs/gemini_defconfig=18=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/gemini_defconfig:19:CONFIG_BINFMT_MISC=y\narch/arm/configs/gemini_defconfig-20-CONFIG_CMA=y\n--\narch/arm/configs/imx_v6_v7_defconfig=56=CONFIG_MODULE_SRCVERSION_ALL=y\narch/arm/configs/imx_v6_v7_defconfig:57:CONFIG_BINFMT_MISC=m\narch/arm/configs/imx_v6_v7_defconfig-58-# CONFIG_COMPAT_BRK is not set\n--\narch/arm/configs/omap1_defconfig=39=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/omap1_defconfig:40:CONFIG_BINFMT_MISC=y\narch/arm/configs/omap1_defconfig-41-# CONFIG_SWAP is not set\n--\narch/arm/configs/omap2plus_defconfig=62=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/omap2plus_defconfig:63:CONFIG_BINFMT_MISC=y\narch/arm/configs/omap2plus_defconfig-64-CONFIG_CMA=y\n--\narch/arm/configs/pxa_defconfig=45=CONFIG_CMDLINE_PARTITION=y\narch/arm/configs/pxa_defconfig:46:CONFIG_BINFMT_MISC=y\narch/arm/configs/pxa_defconfig-47-CONFIG_SLUB_TINY=y\n--\narch/arm/configs/spear13xx_defconfig=19=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/spear13xx_defconfig:20:CONFIG_BINFMT_MISC=y\narch/arm/configs/spear13xx_defconfig-21-CONFIG_NET=y\n--\narch/arm/configs/spear3xx_defconfig=13=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/spear3xx_defconfig:14:CONFIG_BINFMT_MISC=y\narch/arm/configs/spear3xx_defconfig-15-CONFIG_NET=y\n--\narch/arm/configs/spear6xx_defconfig=10=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/spear6xx_defconfig:11:CONFIG_BINFMT_MISC=y\narch/arm/configs/spear6xx_defconfig-12-CONFIG_NET=y\n--\narch/arm/configs/spitz_defconfig=18=CONFIG_PARTITION_ADVANCED=y\narch/arm/configs/spitz_defconfig:19:CONFIG_BINFMT_MISC=m\narch/arm/configs/spitz_defconfig-20-CONFIG_PM=y\n--\narch/loongarch/configs/loongson32_defconfig=93=CONFIG_BFQ_GROUP_IOSCHED=y\narch/loongarch/configs/loongson32_defconfig:94:CONFIG_BINFMT_MISC=m\narch/loongarch/configs/loongson32_defconfig-95-CONFIG_ZSWAP=y\n--\narch/loongarch/configs/loongson64_defconfig=108=CONFIG_BFQ_GROUP_IOSCHED=y\narch/loongarch/configs/loongson64_defconfig:109:CONFIG_BINFMT_MISC=m\narch/loongarch/configs/loongson64_defconfig-110-CONFIG_ZSWAP=y\n--\narch/m68k/configs/amiga_defconfig=42=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/amiga_defconfig-43-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/amiga_defconfig:44:CONFIG_BINFMT_MISC=m\narch/m68k/configs/amiga_defconfig-45-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/apollo_defconfig=38=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/apollo_defconfig-39-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/apollo_defconfig:40:CONFIG_BINFMT_MISC=m\narch/m68k/configs/apollo_defconfig-41-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/atari_defconfig=45=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/atari_defconfig-46-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/atari_defconfig:47:CONFIG_BINFMT_MISC=m\narch/m68k/configs/atari_defconfig-48-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/bvme6000_defconfig=35=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/bvme6000_defconfig-36-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/bvme6000_defconfig:37:CONFIG_BINFMT_MISC=m\narch/m68k/configs/bvme6000_defconfig-38-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/hp300_defconfig=37=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/hp300_defconfig-38-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/hp300_defconfig:39:CONFIG_BINFMT_MISC=m\narch/m68k/configs/hp300_defconfig-40-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/mac_defconfig=36=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/mac_defconfig-37-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/mac_defconfig:38:CONFIG_BINFMT_MISC=m\narch/m68k/configs/mac_defconfig-39-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/multi_defconfig=56=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/multi_defconfig-57-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/multi_defconfig:58:CONFIG_BINFMT_MISC=m\narch/m68k/configs/multi_defconfig-59-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/mvme147_defconfig=34=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/mvme147_defconfig-35-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/mvme147_defconfig:36:CONFIG_BINFMT_MISC=m\narch/m68k/configs/mvme147_defconfig-37-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/mvme16x_defconfig=35=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/mvme16x_defconfig-36-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/mvme16x_defconfig:37:CONFIG_BINFMT_MISC=m\narch/m68k/configs/mvme16x_defconfig-38-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/q40_defconfig=36=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/q40_defconfig-37-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/q40_defconfig:38:CONFIG_BINFMT_MISC=m\narch/m68k/configs/q40_defconfig-39-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/stmark2_defconfig=29=CONFIG_BINFMT_ZFLAT=y\narch/m68k/configs/stmark2_defconfig:30:CONFIG_BINFMT_MISC=y\narch/m68k/configs/stmark2_defconfig-31-# CONFIG_COREDUMP is not set\n--\narch/m68k/configs/sun3_defconfig=32=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/sun3_defconfig-33-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/sun3_defconfig:34:CONFIG_BINFMT_MISC=m\narch/m68k/configs/sun3_defconfig-35-# CONFIG_COMPACTION is not set\n--\narch/m68k/configs/sun3x_defconfig=32=CONFIG_IOSCHED_BFQ=m\narch/m68k/configs/sun3x_defconfig-33-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/m68k/configs/sun3x_defconfig:34:CONFIG_BINFMT_MISC=m\narch/m68k/configs/sun3x_defconfig-35-# CONFIG_COMPACTION is not set\n--\narch/mips/configs/fuloong2e_defconfig=27=CONFIG_PARTITION_ADVANCED=y\narch/mips/configs/fuloong2e_defconfig:28:CONFIG_BINFMT_MISC=y\narch/mips/configs/fuloong2e_defconfig-29-CONFIG_NET=y\n--\narch/mips/configs/gpr_defconfig=17=CONFIG_PARTITION_ADVANCED=y\narch/mips/configs/gpr_defconfig:18:CONFIG_BINFMT_MISC=m\narch/mips/configs/gpr_defconfig-19-CONFIG_NET=y\n--\narch/mips/configs/ip22_defconfig=23=CONFIG_PARTITION_ADVANCED=y\narch/mips/configs/ip22_defconfig:24:CONFIG_BINFMT_MISC=m\narch/mips/configs/ip22_defconfig-25-CONFIG_NET=y\n--\narch/mips/configs/ip32_defconfig=19=CONFIG_SGI_PARTITION=y\narch/mips/configs/ip32_defconfig:20:CONFIG_BINFMT_MISC=y\narch/mips/configs/ip32_defconfig-21-CONFIG_NET=y\n--\narch/mips/configs/jazz_defconfig=17=CONFIG_PARTITION_ADVANCED=y\narch/mips/configs/jazz_defconfig:18:CONFIG_BINFMT_MISC=m\narch/mips/configs/jazz_defconfig-19-CONFIG_NET=y\n--\narch/mips/configs/lemote2f_defconfig=27=CONFIG_MQ_IOSCHED_DEADLINE=m\narch/mips/configs/lemote2f_defconfig:28:CONFIG_BINFMT_MISC=m\narch/mips/configs/lemote2f_defconfig-29-CONFIG_NET=y\n--\narch/mips/configs/loongson2k_defconfig=35=CONFIG_BFQ_GROUP_IOSCHED=y\narch/mips/configs/loongson2k_defconfig:36:CONFIG_BINFMT_MISC=m\narch/mips/configs/loongson2k_defconfig-37-CONFIG_KSM=y\n--\narch/mips/configs/loongson3_defconfig=49=CONFIG_IOSCHED_BFQ=y\narch/mips/configs/loongson3_defconfig:50:CONFIG_BINFMT_MISC=m\narch/mips/configs/loongson3_defconfig-51-CONFIG_KSM=y\n--\narch/mips/configs/mtx1_defconfig=38=CONFIG_KARMA_PARTITION=y\narch/mips/configs/mtx1_defconfig:39:CONFIG_BINFMT_MISC=m\narch/mips/configs/mtx1_defconfig-40-CONFIG_NET=y\n--\narch/mips/configs/pic32mzda_defconfig=24=CONFIG_SGI_PARTITION=y\narch/mips/configs/pic32mzda_defconfig:25:CONFIG_BINFMT_MISC=m\narch/mips/configs/pic32mzda_defconfig-26-CONFIG_DEVTMPFS=y\n--\narch/mips/configs/rm200_defconfig=18=CONFIG_PARTITION_ADVANCED=y\narch/mips/configs/rm200_defconfig:19:CONFIG_BINFMT_MISC=m\narch/mips/configs/rm200_defconfig-20-CONFIG_NET=y\n--\narch/parisc/configs/generic-32bit_defconfig=26=CONFIG_MODULE_FORCE_UNLOAD=y\narch/parisc/configs/generic-32bit_defconfig-27-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/parisc/configs/generic-32bit_defconfig:28:CONFIG_BINFMT_MISC=m\narch/parisc/configs/generic-32bit_defconfig-29-CONFIG_NET=y\n--\narch/parisc/configs/generic-64bit_defconfig=35=CONFIG_BLK_DEV_INTEGRITY=y\narch/parisc/configs/generic-64bit_defconfig:36:CONFIG_BINFMT_MISC=m\narch/parisc/configs/generic-64bit_defconfig-37-# CONFIG_COMPAT_BRK is not set\n--\narch/powerpc/configs/85xx/ge_imp3a_defconfig=28=CONFIG_PREEMPT=y\narch/powerpc/configs/85xx/ge_imp3a_defconfig-29-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/powerpc/configs/85xx/ge_imp3a_defconfig:30:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/85xx/ge_imp3a_defconfig-31-CONFIG_MATH_EMULATION=y\n--\narch/powerpc/configs/85xx/ksi8560_defconfig=12=CONFIG_HIGHMEM=y\narch/powerpc/configs/85xx/ksi8560_defconfig:13:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/85xx/ksi8560_defconfig-14-CONFIG_MATH_EMULATION=y\n--\narch/powerpc/configs/85xx/stx_gp3_defconfig=10=CONFIG_HIGHMEM=y\narch/powerpc/configs/85xx/stx_gp3_defconfig:11:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/85xx/stx_gp3_defconfig-12-CONFIG_MATH_EMULATION=y\n--\narch/powerpc/configs/85xx/tqm8548_defconfig=14=CONFIG_HIGHMEM=y\narch/powerpc/configs/85xx/tqm8548_defconfig:15:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/85xx/tqm8548_defconfig-16-CONFIG_MATH_EMULATION=y\n--\narch/powerpc/configs/amigaone_defconfig=21=CONFIG_HIGHMEM=y\narch/powerpc/configs/amigaone_defconfig:22:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/amigaone_defconfig-23-CONFIG_NET=y\n--\narch/powerpc/configs/cell_defconfig=34=CONFIG_GEN_RTC=y\narch/powerpc/configs/cell_defconfig:35:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/cell_defconfig-36-CONFIG_IRQ_ALL_CPUS=y\n--\narch/powerpc/configs/chrp32_defconfig=20=CONFIG_HIGHMEM=y\narch/powerpc/configs/chrp32_defconfig:21:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/chrp32_defconfig-22-CONFIG_IRQ_ALL_CPUS=y\n--\narch/powerpc/configs/ep8248e_defconfig=11=CONFIG_EP8248E=y\narch/powerpc/configs/ep8248e_defconfig:12:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/ep8248e_defconfig-13-# CONFIG_SECCOMP is not set\n--\narch/powerpc/configs/fsl-emb-nonhw.config=5=CONFIG_BFS_FS=m\narch/powerpc/configs/fsl-emb-nonhw.config:6:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/fsl-emb-nonhw.config-7-# CONFIG_BLK_DEV_BSG is not set\n--\narch/powerpc/configs/gamecube_defconfig=19=CONFIG_PREEMPT=y\narch/powerpc/configs/gamecube_defconfig:20:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/gamecube_defconfig-21-CONFIG_KEXEC=y\n--\narch/powerpc/configs/holly_defconfig=14=CONFIG_GEN_RTC=y\narch/powerpc/configs/holly_defconfig:15:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/holly_defconfig-16-CONFIG_CMDLINE=\"console=ttyS0,115200\"\n--\narch/powerpc/configs/mgcoge_defconfig=16=CONFIG_MGCOGE=y\narch/powerpc/configs/mgcoge_defconfig:17:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/mgcoge_defconfig-18-# CONFIG_SECCOMP is not set\n--\narch/powerpc/configs/pmac32_defconfig=23=CONFIG_HIGHMEM=y\narch/powerpc/configs/pmac32_defconfig:24:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/pmac32_defconfig-25-CONFIG_HIBERNATION=y\n--\narch/powerpc/configs/powernv_defconfig=49=CONFIG_HZ_1000=y\narch/powerpc/configs/powernv_defconfig:50:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/powernv_defconfig-51-CONFIG_PPC_TRANSACTIONAL_MEM=y\n--\narch/powerpc/configs/ppc64_defconfig=79=CONFIG_PARTITION_ADVANCED=y\narch/powerpc/configs/ppc64_defconfig:80:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/ppc64_defconfig-81-CONFIG_ZSWAP=y\n--\narch/powerpc/configs/ppc64e_defconfig=26=CONFIG_CPU_FREQ_GOV_USERSPACE=y\narch/powerpc/configs/ppc64e_defconfig:27:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/ppc64e_defconfig-28-CONFIG_IRQ_ALL_CPUS=y\n--\narch/powerpc/configs/ppc6xx_defconfig=65=CONFIG_PREEMPT_VOLUNTARY=y\narch/powerpc/configs/ppc6xx_defconfig:66:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/ppc6xx_defconfig-67-CONFIG_HIBERNATION=y\n--\narch/powerpc/configs/ps3_defconfig=33=CONFIG_MODULE_UNLOAD=y\narch/powerpc/configs/ps3_defconfig-34-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/powerpc/configs/ps3_defconfig:35:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/ps3_defconfig-36-# CONFIG_COMPAT_BRK is not set\n--\narch/powerpc/configs/storcenter_defconfig=13=CONFIG_HZ_100=y\narch/powerpc/configs/storcenter_defconfig:14:CONFIG_BINFMT_MISC=y\narch/powerpc/configs/storcenter_defconfig-15-CONFIG_CMDLINE=\"console=ttyS0,115200\"\n--\narch/powerpc/configs/wii_defconfig=19=CONFIG_PREEMPT=y\narch/powerpc/configs/wii_defconfig:20:CONFIG_BINFMT_MISC=m\narch/powerpc/configs/wii_defconfig-21-CONFIG_KEXEC=y\n--\narch/s390/configs/debug_defconfig=98=CONFIG_IOSCHED_BFQ=y\narch/s390/configs/debug_defconfig:99:CONFIG_BINFMT_MISC=m\narch/s390/configs/debug_defconfig-100-CONFIG_ZSWAP=y\n--\narch/s390/configs/defconfig=92=CONFIG_IOSCHED_BFQ=y\narch/s390/configs/defconfig:93:CONFIG_BINFMT_MISC=m\narch/s390/configs/defconfig-94-CONFIG_ZSWAP=y\n--\narch/sh/configs/apsh4ad0a_defconfig=40=CONFIG_PREEMPT=y\narch/sh/configs/apsh4ad0a_defconfig-41-# CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS is not set\narch/sh/configs/apsh4ad0a_defconfig:42:CONFIG_BINFMT_MISC=y\narch/sh/configs/apsh4ad0a_defconfig-43-CONFIG_CMDLINE_FROM_BOOTLOADER=y\n--\narch/sh/configs/r7785rp_defconfig=30=CONFIG_PCI=y\narch/sh/configs/r7785rp_defconfig:31:CONFIG_BINFMT_MISC=m\narch/sh/configs/r7785rp_defconfig-32-CONFIG_NET=y\n--\narch/sh/configs/sdk7786_defconfig=74=CONFIG_CORE_DUMP_DEFAULT_ELF_HEADERS=y\narch/sh/configs/sdk7786_defconfig:75:CONFIG_BINFMT_MISC=y\narch/sh/configs/sdk7786_defconfig-76-CONFIG_PM=y\n--\narch/sh/configs/se7206_defconfig=43=CONFIG_BINFMT_ZFLAT=y\narch/sh/configs/se7206_defconfig:44:CONFIG_BINFMT_MISC=y\narch/sh/configs/se7206_defconfig-45-CONFIG_NET=y\n--\narch/sh/configs/sh03_defconfig=21=CONFIG_HOTPLUG_PCI=y\narch/sh/configs/sh03_defconfig:22:CONFIG_BINFMT_MISC=y\narch/sh/configs/sh03_defconfig-23-CONFIG_NET=y\n--\narch/sh/configs/sh2007_defconfig=24=CONFIG_PCCARD=y\narch/sh/configs/sh2007_defconfig:25:CONFIG_BINFMT_MISC=y\narch/sh/configs/sh2007_defconfig-26-CONFIG_NET=y\n--\narch/sh/configs/shx3_defconfig=50=CONFIG_CMDLINE=\"console=ttySC0,115200 earlyprintk=bios ignore_loglevel\"\narch/sh/configs/shx3_defconfig:51:CONFIG_BINFMT_MISC=y\narch/sh/configs/shx3_defconfig-52-CONFIG_NET=y\n--\narch/sh/configs/urquell_defconfig=35=CONFIG_PCI_DEBUG=y\narch/sh/configs/urquell_defconfig:36:CONFIG_BINFMT_MISC=y\narch/sh/configs/urquell_defconfig-37-CONFIG_CMDLINE_FROM_BOOTLOADER=y\n--\narch/sparc/configs/sparc32_defconfig=11=CONFIG_SUN_OPENPROMFS=m\narch/sparc/configs/sparc32_defconfig:12:CONFIG_BINFMT_MISC=m\narch/sparc/configs/sparc32_defconfig-13-CONFIG_NET=y\n--\narch/sparc/configs/sparc64_defconfig=27=CONFIG_SUN_OPENPROMFS=m\narch/sparc/configs/sparc64_defconfig:28:CONFIG_BINFMT_MISC=m\narch/sparc/configs/sparc64_defconfig-29-CONFIG_NET=y\n--\narch/um/configs/i386_defconfig-1-# CONFIG_COMPACTION is not set\narch/um/configs/i386_defconfig:2:CONFIG_BINFMT_MISC=m\narch/um/configs/i386_defconfig-3-CONFIG_HOSTFS=y\n--\narch/um/configs/x86_64_defconfig-1-# CONFIG_COMPACTION is not set\narch/um/configs/x86_64_defconfig:2:CONFIG_BINFMT_MISC=m\narch/um/configs/x86_64_defconfig-3-CONFIG_HOSTFS=y\n--\narch/x86/configs/i386_defconfig=59=CONFIG_BLK_CGROUP_IOPRIO=y\narch/x86/configs/i386_defconfig:60:CONFIG_BINFMT_MISC=y\narch/x86/configs/i386_defconfig-61-# CONFIG_COMPAT_BRK is not set\n--\narch/x86/configs/x86_64_defconfig=60=CONFIG_BLK_CGROUP_IOPRIO=y\narch/x86/configs/x86_64_defconfig:61:CONFIG_BINFMT_MISC=y\narch/x86/configs/x86_64_defconfig-62-# CONFIG_COMPAT_BRK is not set\n--\narch/xtensa/configs/common_defconfig=10=CONFIG_CMDLINE=\"console=ttyS0,38400 ip=bootp root=nfs nfsroot=/opt/montavista/pro/devkit/xtensa/linux_be/target memmap=128M@0\"\narch/xtensa/configs/common_defconfig:11:CONFIG_BINFMT_MISC=y\narch/xtensa/configs/common_defconfig-12-CONFIG_NET=y\n--\nfs/Makefile=34=obj-$(CONFIG_FILE_LOCKING)      += locks.o\nfs/Makefile:35:obj-$(CONFIG_BINFMT_MISC)\t+= binfmt_misc.o\nfs/Makefile-36-obj-$(CONFIG_BINFMT_SCRIPT)\t+= binfmt_script.o\n--\nfs/file_table.c=165=static int __init init_fs_stat_sysctls(void)\n--\nfs/file_table.c-167-\tregister_sysctl_init(\"fs\", fs_stat_sysctls);\nfs/file_table.c:168:\tif (IS_ENABLED(CONFIG_BINFMT_MISC)) {\nfs/file_table.c-169-\t\tstruct ctl_table_header *hdr;\n--\ninclude/linux/binfmts.h=92=struct linux_binfmt {\n--\ninclude/linux/binfmts.h-101-\ninclude/linux/binfmts.h:102:#if IS_ENABLED(CONFIG_BINFMT_MISC)\ninclude/linux/binfmts.h-103-struct binfmt_misc {\n--\ninclude/linux/user_namespace.h=64=enum rlimit_type {\n--\ninclude/linux/user_namespace.h-71-\ninclude/linux/user_namespace.h:72:#if IS_ENABLED(CONFIG_BINFMT_MISC)\ninclude/linux/user_namespace.h-73-struct binfmt_misc;\n--\ninclude/linux/user_namespace.h=76=struct user_namespace {\n--\ninclude/linux/user_namespace.h-113-\ninclude/linux/user_namespace.h:114:#if IS_ENABLED(CONFIG_BINFMT_MISC)\ninclude/linux/user_namespace.h-115-\tstruct binfmt_misc *binfmt_misc;\n--\nkernel/user.c-23-\nkernel/user.c:24:#if IS_ENABLED(CONFIG_BINFMT_MISC)\nkernel/user.c-25-struct binfmt_misc init_binfmt_misc = {\n--\nkernel/user.c=37=struct user_namespace init_user_ns = {\n--\nkernel/user.c-75-#endif\nkernel/user.c:76:#if IS_ENABLED(CONFIG_BINFMT_MISC)\nkernel/user.c-77-\t.binfmt_misc = \u0026init_binfmt_misc,\n--\nkernel/user_namespace.c=197=static void free_user_ns(struct work_struct *work)\n--\nkernel/user_namespace.c-217-\t\t}\nkernel/user_namespace.c:218:#if IS_ENABLED(CONFIG_BINFMT_MISC)\nkernel/user_namespace.c-219-\t\tkfree(ns-\u003ebinfmt_misc);\n--\nnet/core/filter.c=8385=sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)\n--\nnet/core/filter.c-8399-\t\treturn \u0026bpf_skb_event_output_proto;\nnet/core/filter.c:8400:#if IS_BUILTIN(CONFIG_BINFMT_MISC)\nnet/core/filter.c-8401-\tcase BPF_FUNC_binprm_set_interp:\n--\ntools/testing/selftests/bpf/config.aarch64=5=CONFIG_AUDIT=y\ntools/testing/selftests/bpf/config.aarch64:6:CONFIG_BINFMT_MISC=y\ntools/testing/selftests/bpf/config.aarch64-7-CONFIG_BLK_CGROUP=y\n--\ntools/testing/selftests/bpf/config.x86_64=8=CONFIG_BACKLIGHT_CLASS_DEVICE=y\ntools/testing/selftests/bpf/config.x86_64:9:CONFIG_BINFMT_MISC=y\ntools/testing/selftests/bpf/config.x86_64-10-CONFIG_BLK_CGROUP=y\n--\ntools/testing/selftests/hid/config.common=4=CONFIG_AUDIT=y\ntools/testing/selftests/hid/config.common:5:CONFIG_BINFMT_MISC=y\ntools/testing/selftests/hid/config.common-6-CONFIG_BLK_CGROUP_IOLATENCY=y\n"
}

gemini-3.1-pro-preview

null

null

							input: 15381
							output: 36
							thoughts: 179
						

Here's a summary of my thought process:

**Configuration Dependencies for BPF with BINFMT_MISC**

Okay, so I'm looking at how `BINFMT_MISC` and `BPF_SYSCALL` relate, specifically within the context of getting a BPF helper working.  My initial thought is to consider the relevant configs, which I've identified as `BINFMT_MISC` and `BPF_SYSCALL`. Now, I recall seeing some preprocessor directives in `net/core/filter.c` related to `CONFIG_BINFMT_MISC`. Ah, right, there's an `#if IS_BUILTIN(CONFIG_BINFMT_MISC)` block there. That suggests that the BPF helper, at least in that context, is only available if `BINFMT_MISC` is *built-in* to the kernel.

So, digging a little deeper, `IS_BUILTIN(CONFIG_BINFMT_MISC)` is equivalent to `CONFIG_BINFMT_MISC=y`, not a module. Therefore, for the BPF helper to be available, I need to make sure that `BINFMT_MISC` is set to `y` in the kernel configuration. That makes sense, in order to get it loaded.

And, of course, `BPF_SYSCALL` also needs to be enabled, and this likely ties in to `fs/binfmt_misc.c`. Let me double-check `fs/binfmt_misc.c` to confirm that it correctly handles the two configurations, specifically `CONFIG_BPF_SYSCALL` and `CONFIG_BINFMT_MISC`.

{
  "Expression": "CONFIG_BPF_SYSCALL",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c-31-\nfs/binfmt_misc.c:32:#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c-33-#include \u003clinux/bpf.h\u003e\n--\nfs/binfmt_misc.c=57=typedef struct {\n--\nfs/binfmt_misc.c-68-\trefcount_t users;\t\t/* sync removal with load_misc_binary() */\nfs/binfmt_misc.c:69:#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c-70-\tstruct bpf_prog *bpf_prog;\n--\nfs/binfmt_misc.c=74=static struct file_system_type bm_fs_type;\n--\nfs/binfmt_misc.c-90-\nfs/binfmt_misc.c:91:#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c-92-struct binfmt_bpf_interp {\n--\nfs/binfmt_misc.c=121=const struct bpf_func_proto bpf_binprm_set_interp_proto = {\n--\nfs/binfmt_misc.c-127-};\nfs/binfmt_misc.c:128:#endif /* CONFIG_BPF_SYSCALL */\nfs/binfmt_misc.c-129-\n--\nfs/binfmt_misc.c=142=static Node *search_binfmt_handler(struct binfmt_misc *misc,\n--\nfs/binfmt_misc.c-159-\t\tif (test_bit(Bpf, \u0026e-\u003eflags)) {\nfs/binfmt_misc.c:160:#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c-161-\t\t\tif (e-\u003ebpf_prog) {\n--\nfs/binfmt_misc.c=246=static void put_binfmt_handler(Node *e)\n--\nfs/binfmt_misc.c-250-\t\t\tfilp_close(e-\u003einterp_file, NULL);\nfs/binfmt_misc.c:251:#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c-252-\t\tif (test_bit(Bpf, \u0026e-\u003eflags) \u0026\u0026 e-\u003ebpf_prog)\n--\nfs/binfmt_misc.c=455=static Node *create_entry(const char __user *buffer, size_t count)\n--\nfs/binfmt_misc.c-615-\nfs/binfmt_misc.c:616:#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c-617-\t\te-\u003ebpf_prog = bpf_prog_get_type_path(e-\u003emagic, BPF_PROG_TYPE_SOCKET_FILTER);\n"
}

gemini-3.1-pro-preview

null

null

							input: 16675
							output: 30
							thoughts: 66
						

**Kernel BPF Considerations**

Okay, yes, I'm confident that `CONFIG_BPF_SYSCALL` is absolutely necessary for this. But hang on, I see that the code is using `bpf_prog_get_type_path`. Now, is that function even available in this configuration? I need to verify its presence. Let me quickly double-check the availability of `bpf_prog_get_type_path`.

{
  "Expression": "bpf_prog_get_type_path",
  "PathPrefix": ""
}

{
  "Output": "fs/binfmt_misc.c=455=static Node *create_entry(const char __user *buffer, size_t count)\n--\nfs/binfmt_misc.c-616-#ifdef CONFIG_BPF_SYSCALL\nfs/binfmt_misc.c:617:\t\te-\u003ebpf_prog = bpf_prog_get_type_path(e-\u003emagic, BPF_PROG_TYPE_SOCKET_FILTER);\nfs/binfmt_misc.c-618-\t\tif (IS_ERR(e-\u003ebpf_prog)) {\n--\ninclude/linux/bpf.h=3088=static inline int bpf_map_attr_numa_node(const union bpf_attr *attr)\n--\ninclude/linux/bpf.h-3093-\ninclude/linux/bpf.h:3094:struct bpf_prog *bpf_prog_get_type_path(const char *name, enum bpf_prog_type type);\ninclude/linux/bpf.h-3095-int array_map_alloc_check(union bpf_attr *attr);\n--\ninclude/linux/bpf.h=3437=static inline int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,\n--\ninclude/linux/bpf.h-3442-\ninclude/linux/bpf.h:3443:static inline struct bpf_prog *bpf_prog_get_type_path(const char *name,\ninclude/linux/bpf.h-3444-\t\t\t\tenum bpf_prog_type type)\n--\nkernel/bpf/inode.c=611=static struct bpf_prog *__get_prog_inode(struct inode *inode, enum bpf_prog_type type)\n--\nkernel/bpf/inode.c-637-\nkernel/bpf/inode.c:638:struct bpf_prog *bpf_prog_get_type_path(const char *name, enum bpf_prog_type type)\nkernel/bpf/inode.c-639-{\n--\nkernel/bpf/inode.c-650-}\nkernel/bpf/inode.c:651:EXPORT_SYMBOL(bpf_prog_get_type_path);\nkernel/bpf/inode.c-652-\n--\nnet/netfilter/xt_bpf.c=55=static int __bpf_mt_check_path(const char *path, struct bpf_prog **ret)\n--\nnet/netfilter/xt_bpf.c-59-\nnet/netfilter/xt_bpf.c:60:\t*ret = bpf_prog_get_type_path(path, BPF_PROG_TYPE_SOCKET_FILTER);\nnet/netfilter/xt_bpf.c-61-\treturn PTR_ERR_OR_ZERO(*ret);\n"
}

gemini-3.1-pro-preview

null

null

							input: 17584
							output: 33
							thoughts: 385
						

**Analyzing the BPF Interpreter Patch**

Okay, so this patch introduces `bpf_binprm_set_interp`, a new BPF helper, and then fiddles with `binfmt_misc` so that BPF programs can choose an interpreter. Functionally, this looks sound and reachable – good start.

I need to make sure the right kernel configs are enabled: `BINFMT_MISC` and `BPF_SYSCALL`.  Wait a minute... I see `IS_BUILTIN(CONFIG_BINFMT_MISC)` used in `net/core/filter.c`. That implies that `BINFMT_MISC` *must* be built-in, not a module, right?  Hang on, `CONFIG_BINFMT_MISC` can be set to either `y` or `m`. If it's set to `m`, then `IS_BUILTIN` is going to be false. Hmm, this means that we need to ensure it's set to `y` for this to work.  The tool just takes the config name; I can't directly specify `=y`.  I guess syzkaller will handle that bit by enabling it.

Let's quickly outline the core functions involved in this.  We're looking at:

*   `bpf_binprm_set_interp` (the new BPF helper)
*   `search_binfmt_handler`
*   `get_binfmt_handler`
*   `load_misc_binary`
*   `create_entry`
*   `entry_status`

Okay, let's step through this. The BPF helper is `bpf_binprm_set_interp`. `search_binfmt_handler` and `load_misc_binary` are static, and `load_misc_binary` is actually registered as a binfmt handler. And that other one, `create_entry`, is static too, and is called from `bm_register_write`.  Ah, so I should be looking at `fs/binfmt_misc.c` for how `bm_register_write` works.

{
  "Expression": "bm_register_write",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=929=static int add_entry(Node *e, struct super_block *sb)\n--\nfs/binfmt_misc.c-957-\nfs/binfmt_misc.c:958:static ssize_t bm_register_write(struct file *file, const char __user *buffer,\nfs/binfmt_misc.c-959-\t\t\t       size_t count, loff_t *ppos)\n--\nfs/binfmt_misc.c=1002=static const struct file_operations bm_register_operations = {\nfs/binfmt_misc.c:1003:\t.write\t\t= bm_register_write,\nfs/binfmt_misc.c-1004-\t.llseek\t\t= noop_llseek,\n"
}

gemini-3.1-pro-preview

null

null

							input: 18680
							output: 33
							thoughts: 173
						

**Analyzing Binary Loading Functions**

Okay, let's zero in on these functions: `bm_register_write`, `create_entry`, `load_misc_binary`, `bpf_binprm_set_interp`, `search_binfmt_handler`, and `get_binfmt_handler`. I need to understand their static/dynamic nature for this specific analysis.

First, let me confirm: is `load_misc_binary` a static function? Yes, it is. Good. That's one data point.

Now, what about `bpf_binprm_set_interp`? Hmm, it's not a static function. It looks like it's defined with `BPF_CALL_2`. Wait a second… that `BPF_CALL_2` macro is going to expand out to something like `____bpf_binprm_set_interp`. Gotta check that macro to understand the actual function linkage. That's the next step.

{
  "Expression": "BPF_CALL_2",
  "PathPrefix": "include/linux/filter.h"
}

{
  "Output": "include/linux/filter.h=259=static inline bool insn_is_cast_user(const struct bpf_insn *insn)\n--\ninclude/linux/filter.h-624-#define BPF_CALL_1(name, ...)\tBPF_CALL_x(1, __NOATTR, name, __VA_ARGS__)\ninclude/linux/filter.h:625:#define BPF_CALL_2(name, ...)\tBPF_CALL_x(2, __NOATTR, name, __VA_ARGS__)\ninclude/linux/filter.h-626-#define BPF_CALL_3(name, ...)\tBPF_CALL_x(3, __NOATTR, name, __VA_ARGS__)\n"
}

gemini-3.1-pro-preview

null

null

							input: 19285
							output: 34
							thoughts: 31
						

Here's my take on those thoughts, tailored for an expert audience:

**Diving into `bpf_binprm_set_interp` and the BPF JIT**

Okay, so we're looking at `bpf_binprm_set_interp`. That's the entry point, the first place to start, when we're dealing with setting the interpreter for a binary. I need to understand how the BPF infrastructure comes into play here, so I'm going to quickly refresh my memory of `BPF_CALL_x` and see how the BPF JIT gets invoked (if at all) in this path. Let's see how the BPF verifier is being utilized. I'm keen to trace the BPF program execution and understand if there's any manipulation of the program headers, and how that is being managed by the system.

{
  "Expression": "define BPF_CALL_x",
  "PathPrefix": "include/linux/filter.h"
}

{
  "Output": "include/linux/filter.h=259=static inline bool insn_is_cast_user(const struct bpf_insn *insn)\n--\ninclude/linux/filter.h-609-\ninclude/linux/filter.h:610:#define BPF_CALL_x(x, attr, name, ...)\t\t\t\t\t       \\\ninclude/linux/filter.h-611-\tstatic __always_inline\t\t\t\t\t\t       \\\n"
}

gemini-3.1-pro-preview

null

null

							input: 19655
							output: 39
							thoughts: 78
						

Here's my thought process, summarized as if I were considering this myself:

**Examining BPF Function Definitions**

Okay, so I'm looking at how these BPF calls are defined. The macro `BPF_CALL_x` is the key here. It looks like this macro defines `____##name` as an inline function, but *`name`* itself represents the actual underlying function. So, if I'm understanding this correctly, the real function name in this case is `bpf_binprm_set_interp`. I need to confirm this understanding, given the intricacies of BPF and kernel internals.

Now, where can I find the definition and usage of `bpf_binprm_set_interp`? The best place to find this is in `fs/binfmt_misc.c`. I need to look there to confirm my inference and understand what this function is actually doing in the context of `binfmt_misc`. Let me open that file and check.

{
  "Expression": "bpf_binprm_set_interp",
  "PathPrefix": "fs/binfmt_misc.c"
}

{
  "Output": "fs/binfmt_misc.c=96=static DEFINE_PER_CPU(struct binfmt_bpf_interp, binfmt_bpf_interp);\n--\nfs/binfmt_misc.c-98-/*\nfs/binfmt_misc.c:99: * bpf_binprm_set_interp - let a binfmt_misc 'B' program pick the interpreter.\nfs/binfmt_misc.c-100- * @path: interpreter path, in BPF-accessible memory\n--\nfs/binfmt_misc.c-107- */\nfs/binfmt_misc.c:108:BPF_CALL_2(bpf_binprm_set_interp, const char *, path, u32, len)\nfs/binfmt_misc.c-109-{\n--\nfs/binfmt_misc.c-120-\nfs/binfmt_misc.c:121:const struct bpf_func_proto bpf_binprm_set_interp_proto = {\nfs/binfmt_misc.c:122:\t.func\t\t= bpf_binprm_set_interp,\nfs/binfmt_misc.c-123-\t.gpl_only\t= false,\n--\nfs/binfmt_misc.c-134- * @bpf_interp: receives a kmalloc'd interpreter path if a 'B' program chooses\nfs/binfmt_misc.c:135: *              one via bpf_binprm_set_interp(); the caller must kfree() it\nfs/binfmt_misc.c-136- *\n--\nfs/binfmt_misc.c=291=static int load_misc_binary(struct linux_binprm *bprm)\n--\nfs/binfmt_misc.c-309-\t * A 'B' (BPF) handler carries no interpreter of its own; the program\nfs/binfmt_misc.c:310:\t * chooses it via bpf_binprm_set_interp(). Other handlers use the\nfs/binfmt_misc.c-311-\t * interpreter recorded at registration.\n--\nfs/binfmt_misc.c=455=static Node *create_entry(const char __user *buffer, size_t count)\n--\nfs/binfmt_misc.c-677-\t\t * A 'B' (BPF) handler carries no interpreter of its own; the\nfs/binfmt_misc.c:678:\t\t * program picks it via bpf_binprm_set_interp(). Reject a\nfs/binfmt_misc.c-679-\t\t * statically registered one.\n"
}

gemini-3.1-pro-preview

null

null

							input: 20648
							output: 29
							thoughts: 265
						

**My Assessment of the BPF BinFmt_Misc Implementation**

Okay, so I'm looking at this new BPF matching for `binfmt_misc` feature, and the key functions to zero in on seem to be: `bpf_binprm_set_interp`, `search_binfmt_handler`, `get_binfmt_handler`, `load_misc_binary`, `create_entry`, and `bm_register_write`. Those are the obvious points of interaction with the kernel. This looks like a pretty clear functional addition.

The relevant configurations I need to remember are `BINFMT_MISC` (obviously), and `BPF_SYSCALL`. This is absolutely ripe for fuzzing. A new feature like this always adds attack surface. Let's make sure I've got a comprehensive list of dependencies, though.

Right, `CONFIG_BINFMT_MISC` is the primary one, and `CONFIG_BPF_SYSCALL` is the supporting config. I need to make sure I don't miss anything that's implicitly included or assumed. Okay, I see that `BPF_PROG_TYPE_SOCKET_FILTER` is used as well, which is only available if `CONFIG_BPF_SYSCALL` is enabled. Makes sense. Also, `bpf_prog_get_type_path` is called, and that’s defined in `kernel/bpf/inode.c`. That file is only compiled if `CONFIG_BPF_SYSCALL` is enabled, right? I should double-check that. Always trust, but verify, especially when dealing with BPF.

{
  "Expression": "inode\\.o",
  "PathPrefix": "kernel/bpf/Makefile"
}

{
  "Output": "kernel/bpf/Makefile=7=CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)\nkernel/bpf/Makefile-8-\nkernel/bpf/Makefile:9:obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o\nkernel/bpf/Makefile-10-obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o\n"
}

gemini-3.1-pro-preview

null

null

							input: 21459
							output: 161
							thoughts: 229
						

**Analyzing BPF and Binary Format Registration**

Okay, so I've confirmed that `inode.o` gets compiled when `CONFIG_BPF_SYSCALL` is enabled. That's good to know, sets the stage for what I'm about to do. I need to nail down the interconnections.

Let's see, my key symbols for examination are: `bpf_binprm_set_interp`, `search_binfmt_handler`, `get_binfmt_handler`, `load_misc_binary`, `create_entry`, and `bm_register_write`.

Wait a minute, `bpf_binprm_set_interp` that's a BPF helper! It's invoked by BPF programs, interesting. And now that I think about it, `search_binfmt_handler` is called by `get_binfmt_handler`, which is, in turn, called by `load_misc_binary`. Ah-ha, `load_misc_binary` is triggered during the actual execution of a binary. And it seems that `create_entry` is called from `bm_register_write`, which makes sense because `bm_register_write` is called when writing to `/proc/sys/fs/binfmt_misc/register`.

Alright, these are all solid focus symbols, they seem to highlight the right areas. I'm satisfied. I'll finalize the results based on this understanding.

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "bpf_binprm_set_interp",
    "search_binfmt_handler",
    "get_binfmt_handler",
    "load_misc_binary",
    "create_entry",
    "bm_register_write"
  ],
  "Reasoning": "The patch introduces a new 'B' (BPF) handler type for binfmt_misc, allowing BPF programs to match binaries and select interpreters. This adds new reachable core logic in binfmt_misc registration and binary execution paths, as well as a new BPF helper function.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BINFMT_MISC",
    "BPF_SYSCALL"
  ],
  "FocusSymbols": [
    "bpf_binprm_set_interp",
    "search_binfmt_handler",
    "get_binfmt_handler",
    "load_misc_binary",
    "create_entry",
    "bm_register_write"
  ],
  "Reasoning": "The patch introduces a new 'B' (BPF) handler type for binfmt_misc, allowing BPF programs to match binaries and select interpreters. This adds new reachable core logic in binfmt_misc registration and binary execution paths, as well as a new BPF helper function.",
  "WorthFuzzing": true
}