AI Trajectory

null

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "bpf_struct_ops_desc_init",
    "bpf_check_attach_target",
    "bpf_check_attach_btf_id_multi"
  ],
  "Reasoning": "The patch adds validation in the BPF verifier and struct_ops initialization to reject attaching BPF programs to functions with return values larger than 8 bytes (e.g., __int128) when the attach type uses the trampoline return value. This is reachable via the bpf() syscall.",
  "WorthFuzzing": true
}

null

{
  "PatchDiff": "commit 77ad48beeb4c0c194a306715719f753778c15806\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Sat Jul 11 11:47:27 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c\nindex 51b16e5f5534e0..bbb44ef8f87aa6 100644\n--- a/kernel/bpf/bpf_struct_ops.c\n+++ b/kernel/bpf/bpf_struct_ops.c\n@@ -445,6 +445,18 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,\n \t\t\tgoto errout;\n \t\t}\n \n+\t\t/*\n+\t\t * A \u003e8 byte return value is passed back in the R0:R2 register\n+\t\t * pair, which the struct_ops trampoline does not preserve (only\n+\t\t * 8 bytes of the return value are saved and restored).\n+\t\t */\n+\t\tif (st_ops-\u003efunc_models[i].ret_size \u003e 8) {\n+\t\t\tpr_warn(\"func ptr %s in struct %s has a \u003e8 byte return value, which is not supported\\n\",\n+\t\t\t\tmname, st_ops-\u003ename);\n+\t\t\terr = -EOPNOTSUPP;\n+\t\t\tgoto errout;\n+\t\t}\n+\n \t\tstub_func_addr = *(void **)(st_ops-\u003ecfi_stubs + moff);\n \t\terr = prepare_arg_info(btf, st_ops-\u003ename, mname,\n \t\t\t\t       func_proto, stub_func_addr,\ndiff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c\nindex 6515d4d3c0032f..26d281b77a6e72 100644\n--- a/kernel/bpf/verifier.c\n+++ b/kernel/bpf/verifier.c\n@@ -18873,6 +18873,20 @@ static int btf_id_allow_sleepable(u32 btf_id, unsigned long addr, const struct b\n \treturn -EINVAL;\n }\n \n+static bool attach_uses_trampoline_retval(enum bpf_attach_type type)\n+{\n+\tswitch (type) {\n+\tcase BPF_MODIFY_RETURN:\n+\tcase BPF_TRACE_FEXIT:\n+\tcase BPF_TRACE_FEXIT_MULTI:\n+\tcase BPF_TRACE_FSESSION:\n+\tcase BPF_TRACE_FSESSION_MULTI:\n+\t\treturn true;\n+\tdefault:\n+\t\treturn false;\n+\t}\n+}\n+\n int bpf_check_attach_target(struct bpf_verifier_log *log,\n \t\t\t    const struct bpf_prog *prog,\n \t\t\t    const struct bpf_prog *tgt_prog,\n@@ -19137,6 +19151,14 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,\n \t\tif (ret \u003c 0)\n \t\t\treturn ret;\n \n+\t\tif (tgt_info-\u003efmodel.ret_size \u003e 8 \u0026\u0026\n+\t\t    attach_uses_trampoline_retval(prog-\u003eexpected_attach_type)) {\n+\t\t\tbpf_log(log,\n+\t\t\t\t\"Attach to function %s with a \u003e8 byte return value is not supported for this attach type\\n\",\n+\t\t\t\ttname);\n+\t\t\treturn -EOPNOTSUPP;\n+\t\t}\n+\n \t\t/*\n \t\t * *.multi programs don't need an address during program\n \t\t * verification, we just take the module ref if needed.\n@@ -19413,6 +19435,9 @@ int bpf_check_attach_btf_id_multi(struct btf *btf, struct bpf_prog *prog, u32 bt\n \terr = btf_distill_func_proto(NULL, btf, t, tname, \u0026tgt_info-\u003efmodel);\n \tif (err \u003c 0)\n \t\treturn err;\n+\tif (tgt_info-\u003efmodel.ret_size \u003e 8 \u0026\u0026\n+\t    attach_uses_trampoline_retval(prog-\u003eexpected_attach_type))\n+\t\treturn -EOPNOTSUPP;\n \tif (btf_is_module(btf)) {\n \t\t/* The bpf program already holds reference to module. */\n \t\tif (WARN_ON_ONCE(!prog-\u003eaux-\u003emod))\ndiff --git a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c\nindex f9f9e1cb87bf1c..6c199f5ff4db8a 100644\n--- a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c\n+++ b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c\n@@ -76,6 +76,14 @@ static void test_fexit_noreturns(void)\n \t\t\t       \"Attaching fexit/fsession/fmod_ret to __noreturn function 'do_exit' is rejected.\");\n }\n \n+#ifdef __SIZEOF_INT128__\n+static void test_fexit_int128_ret(void)\n+{\n+\ttest_tracing_fail_prog(\"fexit_int128_ret\",\n+\t\t\t       \"with a \u003e8 byte return value is not supported for this attach type\");\n+}\n+#endif\n+\n void test_tracing_failure(void)\n {\n \tif (test__start_subtest(\"bpf_spin_lock\"))\n@@ -86,4 +94,8 @@ void test_tracing_failure(void)\n \t\ttest_tracing_deny();\n \tif (test__start_subtest(\"fexit_noreturns\"))\n \t\ttest_fexit_noreturns();\n+#ifdef __SIZEOF_INT128__\n+\tif (test__start_subtest(\"fexit_int128_ret\"))\n+\t\ttest_fexit_int128_ret();\n+#endif\n }\ndiff --git a/tools/testing/selftests/bpf/progs/tracing_failure.c b/tools/testing/selftests/bpf/progs/tracing_failure.c\nindex 65e485c4468c62..f7a09576767954 100644\n--- a/tools/testing/selftests/bpf/progs/tracing_failure.c\n+++ b/tools/testing/selftests/bpf/progs/tracing_failure.c\n@@ -30,3 +30,9 @@ int BPF_PROG(fexit_noreturns)\n {\n \treturn 0;\n }\n+\n+SEC(\"?fexit/bpf_testmod_test_int128_ret\")\n+int BPF_PROG(fexit_int128_ret)\n+{\n+\treturn 0;\n+}\ndiff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c\nindex 30f1cd23093cbe..902dbf6582506f 100644\n--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c\n+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c\n@@ -161,6 +161,15 @@ bpf_testmod_test_arg_ptr_to_struct(struct bpf_testmod_struct_arg_1 *a) {\n \treturn bpf_testmod_test_struct_arg_result;\n }\n \n+#ifdef __SIZEOF_INT128__\n+noinline __int128\n+bpf_testmod_test_int128_ret(int a)\n+{\n+\tbpf_testmod_test_struct_arg_result = a;\n+\treturn (__int128)a;\n+}\n+#endif\n+\n __weak noinline void bpf_testmod_looooooooooooooooooooooooooooooong_name(void)\n {\n }\n@@ -514,6 +523,10 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,\n \n \t(void)bpf_testmod_test_arg_ptr_to_struct(\u0026struct_arg1_2);\n \n+#ifdef __SIZEOF_INT128__\n+\t(void)bpf_testmod_test_int128_ret(i);\n+#endif\n+\n \t(void)trace_bpf_testmod_test_raw_tp_null_tp(NULL);\n \n \tbpf_testmod_test_struct_ops3();\n"
}

gemini-3.1-pro-preview

null

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "bpf_struct_ops_desc_init",
    "bpf_check_attach_target",
    "bpf_check_attach_btf_id_multi"
  ],
  "Reasoning": "The patch adds validation in the BPF verifier and struct_ops initialization to reject attaching BPF programs to functions with return values larger than 8 bytes (e.g., __int128) when the attach type uses the trampoline return value. This is reachable via the bpf() syscall.",
  "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 77ad48beeb4c0c194a306715719f753778c15806
Author: syz-cluster <triage@syzkaller.com>
Date:   Sat Jul 11 11:47:27 2026 +0000

    syz-cluster: applied patch under review

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 51b16e5f5534e0..bbb44ef8f87aa6 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -445,6 +445,18 @@ int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,
 			goto errout;
 		}
 
+		/*
+		 * A >8 byte return value is passed back in the R0:R2 register
+		 * pair, which the struct_ops trampoline does not preserve (only
+		 * 8 bytes of the return value are saved and restored).
+		 */
+		if (st_ops->func_models[i].ret_size > 8) {
+			pr_warn("func ptr %s in struct %s has a >8 byte return value, which is not supported\n",
+				mname, st_ops->name);
+			err = -EOPNOTSUPP;
+			goto errout;
+		}
+
 		stub_func_addr = *(void **)(st_ops->cfi_stubs + moff);
 		err = prepare_arg_info(btf, st_ops->name, mname,
 				       func_proto, stub_func_addr,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6515d4d3c0032f..26d281b77a6e72 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -18873,6 +18873,20 @@ static int btf_id_allow_sleepable(u32 btf_id, unsigned long addr, const struct b
 	return -EINVAL;
 }
 
+static bool attach_uses_trampoline_retval(enum bpf_attach_type type)
+{
+	switch (type) {
+	case BPF_MODIFY_RETURN:
+	case BPF_TRACE_FEXIT:
+	case BPF_TRACE_FEXIT_MULTI:
+	case BPF_TRACE_FSESSION:
+	case BPF_TRACE_FSESSION_MULTI:
+		return true;
+	default:
+		return false;
+	}
+}
+
 int bpf_check_attach_target(struct bpf_verifier_log *log,
 			    const struct bpf_prog *prog,
 			    const struct bpf_prog *tgt_prog,
@@ -19137,6 +19151,14 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 		if (ret < 0)
 			return ret;
 
+		if (tgt_info->fmodel.ret_size > 8 &&
+		    attach_uses_trampoline_retval(prog->expected_attach_type)) {
+			bpf_log(log,
+				"Attach to function %s with a >8 byte return value is not supported for this attach type\n",
+				tname);
+			return -EOPNOTSUPP;
+		}
+
 		/*
 		 * *.multi programs don't need an address during program
 		 * verification, we just take the module ref if needed.
@@ -19413,6 +19435,9 @@ int bpf_check_attach_btf_id_multi(struct btf *btf, struct bpf_prog *prog, u32 bt
 	err = btf_distill_func_proto(NULL, btf, t, tname, &tgt_info->fmodel);
 	if (err < 0)
 		return err;
+	if (tgt_info->fmodel.ret_size > 8 &&
+	    attach_uses_trampoline_retval(prog->expected_attach_type))
+		return -EOPNOTSUPP;
 	if (btf_is_module(btf)) {
 		/* The bpf program already holds reference to module. */
 		if (WARN_ON_ONCE(!prog->aux->mod))
diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
index f9f9e1cb87bf1c..6c199f5ff4db8a 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
@@ -76,6 +76,14 @@ static void test_fexit_noreturns(void)
 			       "Attaching fexit/fsession/fmod_ret to __noreturn function 'do_exit' is rejected.");
 }
 
+#ifdef __SIZEOF_INT128__
+static void test_fexit_int128_ret(void)
+{
+	test_tracing_fail_prog("fexit_int128_ret",
+			       "with a >8 byte return value is not supported for this attach type");
+}
+#endif
+
 void test_tracing_failure(void)
 {
 	if (test__start_subtest("bpf_spin_lock"))
@@ -86,4 +94,8 @@ void test_tracing_failure(void)
 		test_tracing_deny();
 	if (test__start_subtest("fexit_noreturns"))
 		test_fexit_noreturns();
+#ifdef __SIZEOF_INT128__
+	if (test__start_subtest("fexit_int128_ret"))
+		test_fexit_int128_ret();
+#endif
 }
diff --git a/tools/testing/selftests/bpf/progs/tracing_failure.c b/tools/testing/selftests/bpf/progs/tracing_failure.c
index 65e485c4468c62..f7a09576767954 100644
--- a/tools/testing/selftests/bpf/progs/tracing_failure.c
+++ b/tools/testing/selftests/bpf/progs/tracing_failure.c
@@ -30,3 +30,9 @@ int BPF_PROG(fexit_noreturns)
 {
 	return 0;
 }
+
+SEC("?fexit/bpf_testmod_test_int128_ret")
+int BPF_PROG(fexit_int128_ret)
+{
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index 30f1cd23093cbe..902dbf6582506f 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -161,6 +161,15 @@ bpf_testmod_test_arg_ptr_to_struct(struct bpf_testmod_struct_arg_1 *a) {
 	return bpf_testmod_test_struct_arg_result;
 }
 
+#ifdef __SIZEOF_INT128__
+noinline __int128
+bpf_testmod_test_int128_ret(int a)
+{
+	bpf_testmod_test_struct_arg_result = a;
+	return (__int128)a;
+}
+#endif
+
 __weak noinline void bpf_testmod_looooooooooooooooooooooooooooooong_name(void)
 {
 }
@@ -514,6 +523,10 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
 
 	(void)bpf_testmod_test_arg_ptr_to_struct(&struct_arg1_2);
 
+#ifdef __SIZEOF_INT128__
+	(void)bpf_testmod_test_int128_ret(i);
+#endif
+
 	(void)trace_bpf_testmod_test_raw_tp_null_tp(NULL);
 
 	bpf_testmod_test_struct_ops3();

gemini-3.1-pro-preview

null

null

							input: 3825
							output: 24
							thoughts: 414
						

**My Assessment of the BPF Return Value Size Patch**

Okay, so I'm looking at this patch and it's making a specific change in how we handle return values in BPF programs, specifically those larger than 8 bytes. The core of it seems to be in `bpf_struct_ops.c` and the verifier (`verifier.c`).

Essentially, the patch introduces checks to *reject* BPF programs that are trying to attach to functions returning values greater than 8 bytes, like `__int128`. It's doing this through a few key additions:

*   In `bpf_struct_ops_desc_init`, it's now checking `st_ops->func_models[i].ret_size` against 8 bytes, and if it's too large, it throws an `-EOPNOTSUPP` error.
*   The verifier gets a new function, `attach_uses_trampoline_retval()`, likely to determine if a trampoline is being used.
*   Within `bpf_check_attach_target` and `bpf_check_attach_btf_id_multi`, there are checks using `tgt_info->fmodel.ret_size` in conjunction with `attach_uses_trampoline_retval()` to enforce this size limit before allowing the program to attach.

This is a **functional change**. It modifies existing logic in the BPF verifier and the struct\_ops initialization. Before this, these programs might have been allowed, but probably were broken due to the limitations of the trampoline mechanism in handling return values larger than 8 bytes.

Given that it modifies the verifier and initialization logic, I definitely think fuzzing is warranted here. We need to focus on those key symbols: `bpf_struct_ops_desc_init`, `bpf_check_attach_target`, and `bpf_check_attach_btf_id_multi`.

Now, to assess the fuzzing strategy, I should quickly verify if `bpf_struct_ops_desc_init` is reachable. I also need to verify that `bpf_check_attach_target` and `bpf_check_attach_btf_id_multi` are part of the verifier code, which I *know* is reachable. It's in the control plane, not the data path, so it isn't performance-critical code.

I'm going to do a quick grep to make sure I haven't missed anything crucial regarding those symbols and configuration options.

{
  "Expression": "bpf_struct_ops_desc_init"
}

{
  "Output": "include/linux/bpf.h=2262=int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,\n--\ninclude/linux/bpf.h-2264-#endif\ninclude/linux/bpf.h:2265:int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,\ninclude/linux/bpf.h-2266-\t\t\t     struct btf *btf,\n--\nkernel/bpf/bpf_struct_ops.c=324=int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)\n--\nkernel/bpf/bpf_struct_ops.c-330-\nkernel/bpf/bpf_struct_ops.c:331:int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc,\nkernel/bpf/bpf_struct_ops.c-332-\t\t\t     struct btf *btf,\n--\nkernel/bpf/btf.c=9835=btf_add_struct_ops(struct btf *btf, struct bpf_struct_ops *st_ops,\n--\nkernel/bpf/btf.c-9866-\nkernel/bpf/btf.c:9867:\terr = bpf_struct_ops_desc_init(\u0026tab-\u003eops[btf-\u003estruct_ops_tab-\u003ecnt], btf, log);\nkernel/bpf/btf.c-9868-\tif (err)\n"
}

gemini-3.1-pro-preview

null

null

							input: 5229
							output: 30
							thoughts: 49
						

Okay, here's my take on those thoughts, framed from my own expert perspective:

**Kernel BPF Configuration Considerations**

Right, so we're diving into kernel BPF configuration. The first thing that jumps out is that `BPF_SYSCALL` is *the* key enabler here. Without that, we're not going anywhere. It's the lynchpin for everything. Now, to really understand how this impacts the system, I need to dig into the implementation details. Specifically, I'm thinking I should start by examining two files: `kernel/bpf/bpf_struct_ops.c` and `kernel/bpf/verifier.c`. `bpf_struct_ops.c` will show me how they're handling structures within the BPF system and operations, while `verifier.c` is going to be crucial for understanding the crucial security checks and validation steps. Understanding the interaction between these two is key to really grasping the configuration's implications. It will really let me understand if any important nuances or limitations are present.

{
  "Expression": "CONFIG_BPF",
  "PathPrefix": "kernel/bpf/Makefile"
}

{
  "Output": "kernel/bpf/Makefile=2=obj-y := core.o\nkernel/bpf/Makefile:3:ifneq ($(CONFIG_BPF_JIT_ALWAYS_ON),y)\nkernel/bpf/Makefile-4-# ___bpf_prog_run() needs GCSE disabled on x86; see 3193c0836f203 for details\n--\nkernel/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-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o\nkernel/bpf/Makefile:11:obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o\nkernel/bpf/Makefile:12:obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o bpf_insn_array.o\nkernel/bpf/Makefile:13:obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o\nkernel/bpf/Makefile:14:obj-$(CONFIG_BPF_SYSCALL) += fixups.o cfg.o states.o backtrack.o check_btf.o\nkernel/bpf/Makefile:15:obj-${CONFIG_BPF_LSM}\t  += bpf_inode_storage.o\nkernel/bpf/Makefile:16:obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o\nkernel/bpf/Makefile:17:obj-$(CONFIG_BPF_JIT) += trampoline.o\nkernel/bpf/Makefile:18:obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o stream.o\nkernel/bpf/Makefile-19-ifeq ($(CONFIG_MMU)$(CONFIG_64BIT),yy)\nkernel/bpf/Makefile:20:obj-$(CONFIG_BPF_SYSCALL) += arena.o range_tree.o\nkernel/bpf/Makefile-21-endif\nkernel/bpf/Makefile:22:obj-$(CONFIG_BPF_JIT) += dispatcher.o\nkernel/bpf/Makefile-23-ifeq ($(CONFIG_NET),y)\nkernel/bpf/Makefile:24:obj-$(CONFIG_BPF_SYSCALL) += devmap.o\nkernel/bpf/Makefile:25:obj-$(CONFIG_BPF_SYSCALL) += cpumap.o\nkernel/bpf/Makefile:26:obj-$(CONFIG_BPF_SYSCALL) += offload.o\nkernel/bpf/Makefile:27:obj-$(CONFIG_BPF_SYSCALL) += net_namespace.o\nkernel/bpf/Makefile:28:obj-$(CONFIG_BPF_SYSCALL) += tcx.o\nkernel/bpf/Makefile-29-endif\nkernel/bpf/Makefile=30=ifeq ($(CONFIG_PERF_EVENTS),y)\nkernel/bpf/Makefile:31:obj-$(CONFIG_BPF_SYSCALL) += stackmap.o\nkernel/bpf/Makefile-32-endif\nkernel/bpf/Makefile=33=ifeq ($(CONFIG_CGROUPS),y)\nkernel/bpf/Makefile:34:obj-$(CONFIG_BPF_SYSCALL) += cgroup_iter.o bpf_cgrp_storage.o\nkernel/bpf/Makefile-35-endif\n--\nkernel/bpf/Makefile=37=ifeq ($(CONFIG_INET),y)\nkernel/bpf/Makefile:38:obj-$(CONFIG_BPF_SYSCALL) += reuseport_array.o\nkernel/bpf/Makefile-39-endif\n--\nkernel/bpf/Makefile=42=endif\nkernel/bpf/Makefile:43:ifeq ($(CONFIG_BPF_JIT),y)\nkernel/bpf/Makefile:44:obj-$(CONFIG_BPF_SYSCALL) += bpf_struct_ops.o\nkernel/bpf/Makefile:45:obj-$(CONFIG_BPF_SYSCALL) += cpumask.o\nkernel/bpf/Makefile-46-# bpf_lsm_proto.o must precede bpf_lsm.o. The current pahole logic\n--\nkernel/bpf/Makefile-55-# semantics within pahole are revisited accordingly.\nkernel/bpf/Makefile:56:obj-${CONFIG_BPF_LSM} += bpf_lsm_proto.o bpf_lsm.o\nkernel/bpf/Makefile-57-endif\nkernel/bpf/Makefile=58=ifneq ($(CONFIG_CRYPTO),)\nkernel/bpf/Makefile:59:obj-$(CONFIG_BPF_SYSCALL) += crypto.o\nkernel/bpf/Makefile-60-endif\nkernel/bpf/Makefile:61:obj-$(CONFIG_BPF_PRELOAD) += preload/\nkernel/bpf/Makefile-62-\nkernel/bpf/Makefile:63:obj-$(CONFIG_BPF_SYSCALL) += relo_core.o\nkernel/bpf/Makefile:64:obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o\nkernel/bpf/Makefile:65:obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o\nkernel/bpf/Makefile:66:obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o\nkernel/bpf/Makefile-67-ifeq ($(CONFIG_DMA_SHARED_BUFFER),y)\nkernel/bpf/Makefile:68:obj-$(CONFIG_BPF_SYSCALL) += dmabuf_iter.o\nkernel/bpf/Makefile-69-endif\n"
}

gemini-3.1-pro-preview

null

null

							input: 7074
							output: 36
							thoughts: 332
						

**Analyzing BPF Module Dependencies**

Okay, so I'm digging into this BPF patch and need to figure out the configuration dependencies. It's pretty clear that `CONFIG_BPF_SYSCALL` and `CONFIG_BPF_JIT` are going to be required, especially since they're needed for `bpf_struct_ops.o`. The verifier itself is, of course, built with `CONFIG_BPF_SYSCALL`, so that's a given.

Now, I need to see if there are any *specific* configurations tied to this test module. The test module in question is `bpf_testmod.c`. I'd typically expect to see something like `CONFIG_BPF_KPROBE_OVERRIDE` or a similar flag involved in its build, but since this patch is touching core BPF logic, it might be different.

Let's break down the key symbols the patch focuses on: `bpf_struct_ops_desc_init`, `bpf_check_attach_target`, and `bpf_check_attach_btf_id_multi`. Right, the first thing is to verify if `bpf_struct_ops_desc_init` is even reachable. Looking at the code, it's called from `btf_add_struct_ops`, which makes sense. `btf_add_struct_ops`, in turn, is invoked when BTF is being loaded. Good. `bpf_check_attach_target` is called during BPF program attachment. And `bpf_check_attach_btf_id_multi` is specifically for multi-program attachments.

Okay, so all of these are clearly reachable from user-space through the `bpf()` syscall. That's good, that confirms that these can be triggered from user-space.

Just to be absolutely certain, let's circle back to the necessary configurations again. We have to confirm that `CONFIG_BPF_SYSCALL` and `CONFIG_BPF_JIT` are the only *critical* ones, at least for the core functionality.

Finally, I should double-check how `bpf_check_attach_target` is being used, specifically in `kernel/bpf/verifier.c` to look for anything I've missed. It pays to be thorough with the verifier.

{
  "Expression": "bpf_check_attach_target",
  "PathPrefix": "kernel/bpf/verifier.c"
}

{
  "Output": "kernel/bpf/verifier.c=11888=static int process_kf_arg_ptr_to_rbtree_node(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-11899- * LSM hooks and iters (both sleepable and non-sleepable) are safe.\nkernel/bpf/verifier.c:11900: * Any sleepable progs are also safe since bpf_check_attach_target() enforce\nkernel/bpf/verifier.c-11901- * them can only be attached to some specific hook points.\n--\nkernel/bpf/verifier.c=18876=static bool attach_uses_trampoline_retval(enum bpf_attach_type type)\n--\nkernel/bpf/verifier.c-18889-\nkernel/bpf/verifier.c:18890:int bpf_check_attach_target(struct bpf_verifier_log *log,\nkernel/bpf/verifier.c-18891-\t\t\t    const struct bpf_prog *prog,\n--\nkernel/bpf/verifier.c=19303=static int check_attach_btf_id(struct bpf_verifier_env *env)\n--\nkernel/bpf/verifier.c-19333-\nkernel/bpf/verifier.c:19334:\tret = bpf_check_attach_target(\u0026env-\u003elog, prog, tgt_prog, btf_id, \u0026tgt_info);\nkernel/bpf/verifier.c-19335-\tif (ret)\n"
}

gemini-3.1-pro-preview

null

null

							input: 8352
							output: 41
							thoughts: 53
						

Okay, here's my take on those thoughts, framed as my own mental processing:

**Delving into eBPF Attachment Validation**

Right, so I'm tracing the execution path and trying to understand the attachment validation process. It's clear that `bpf_check_attach_target` gets invoked from `check_attach_btf_id`, which is a key component of the verifier. That confirms my initial understanding. Now I need to see how the system handles multiple attachment points. I'm going to look more closely at `bpf_check_attach_btf_id_multi` to understand how that works.

{
  "Expression": "bpf_check_attach_btf_id_multi",
  "PathPrefix": "kernel/bpf/verifier.c"
}

{
  "Output": "kernel/bpf/verifier.c=19303=static int check_attach_btf_id(struct bpf_verifier_env *env)\n--\nkernel/bpf/verifier.c-19402-\nkernel/bpf/verifier.c:19403:int bpf_check_attach_btf_id_multi(struct btf *btf, struct bpf_prog *prog, u32 btf_id,\nkernel/bpf/verifier.c-19404-\t\t\t\t  struct bpf_attach_target_info *tgt_info)\n"
}

gemini-3.1-pro-preview

null

null

							input: 8736
							output: 27
							thoughts: 20
						

Okay, here's my summarized thought process, assuming I'm an expert and this is the context:

**Investigating Function Usage**

Alright, this function... it's either exported or used outside of its current scope. My immediate instinct is to understand its broader impact. I need to figure out where this function is called. Understanding its dependencies and the other parts of the system that rely on it is absolutely crucial. I need to trace its usage to gain a complete understanding of its implications. That's the priority right now.

{
  "Expression": "bpf_check_attach_btf_id_multi"
}

{
  "Output": "include/linux/bpf_verifier.h=1592=int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,\n--\ninclude/linux/bpf_verifier.h-1595-/* Functions exported from verifier.c, used by trampoline.c */\ninclude/linux/bpf_verifier.h:1596:int bpf_check_attach_btf_id_multi(struct btf *btf, struct bpf_prog *prog, u32 btf_id,\ninclude/linux/bpf_verifier.h-1597-\t\t\t\t  struct bpf_attach_target_info *tgt_info);\n--\nkernel/bpf/trampoline.c=1611=int bpf_trampoline_multi_attach(struct bpf_prog *prog, u32 *ids,\n--\nkernel/bpf/trampoline.c-1624-\nkernel/bpf/trampoline.c:1625:\t\terr = bpf_check_attach_btf_id_multi(btf, prog, ids[i], \u0026tgt_info);\nkernel/bpf/trampoline.c-1626-\t\tif (err)\n--\nkernel/bpf/verifier.c=19303=static int check_attach_btf_id(struct bpf_verifier_env *env)\n--\nkernel/bpf/verifier.c-19402-\nkernel/bpf/verifier.c:19403:int bpf_check_attach_btf_id_multi(struct btf *btf, struct bpf_prog *prog, u32 btf_id,\nkernel/bpf/verifier.c-19404-\t\t\t\t  struct bpf_attach_target_info *tgt_info)\n"
}

gemini-3.1-pro-preview

null

null

							input: 9349
							output: 148
							thoughts: 246
						

**My Assessment of the BPF Trampoline Return Value Patch**

Okay, so this patch originates from `bpf_trampoline_multi_attach`. The core of this change focuses on preventing a BPF program from being attached to functions that return values larger than 8 bytes, specifically those like `__int128`, when using the trampoline return value attach type. This is a functional change, reachable through the `bpf()` syscall, which is important to consider in the overall security profile.

From an analysis perspective, it looks like `BPF_SYSCALL` and `BPF_JIT` are the necessary configurations to expose this functionality. The change touches key areas, which means it should be scrutinized:  specifically, `bpf_struct_ops_desc_init`, `bpf_check_attach_target`, and `bpf_check_attach_btf_id_multi`. These seem to be the primary points of validation and checking within the BPF verifier and struct_ops initialization related to this constraint.

Based on this analysis, I'm confident in setting the results: `WorthFuzzing` should be `true`, because the changes here deal with the validation of return value sizes, and syscalls are always a good area to focus on. EnableConfigs are clearly `["BPF_SYSCALL", "BPF_JIT"]`, and the critical `FocusSymbols` are `["bpf_struct_ops_desc_init", "bpf_check_attach_target", "bpf_check_attach_btf_id_multi"]`. The reasoning should be: "The patch adds validation in the BPF verifier and struct_ops initialization to reject attaching BPF programs to functions with return values larger than 8 bytes (e.g., __int128) when the attach type uses the trampoline return value. This is reachable via the bpf() syscall."

Now I will call `set-results` with these values.

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "bpf_struct_ops_desc_init",
    "bpf_check_attach_target",
    "bpf_check_attach_btf_id_multi"
  ],
  "Reasoning": "The patch adds validation in the BPF verifier and struct_ops initialization to reject attaching BPF programs to functions with return values larger than 8 bytes (e.g., __int128) when the attach type uses the trampoline return value. This is reachable via the bpf() syscall.",
  "WorthFuzzing": true
}

{
  "EnableConfigs": [
    "BPF_SYSCALL",
    "BPF_JIT"
  ],
  "FocusSymbols": [
    "bpf_struct_ops_desc_init",
    "bpf_check_attach_target",
    "bpf_check_attach_btf_id_multi"
  ],
  "Reasoning": "The patch adds validation in the BPF verifier and struct_ops initialization to reject attaching BPF programs to functions with return values larger than 8 bytes (e.g., __int128) when the attach type uses the trampoline return value. This is reachable via the bpf() syscall.",
  "WorthFuzzing": true
}