Add a struct_ops member to bpf_testmod whose argument struct carries two task pointers, one plain and one __nullable, both made trusted through a __safe_trusted alias of the struct in the module BTF, and a kfunc that calls the member once with the nullable pointer unset and once set. The callback acquires the plain pointer as is and the nullable one only after a check, driven through the kfunc from a syscall program. The failure case passes the nullable pointer to bpf_task_acquire() unchecked and is rejected as possibly NULL. Signed-off-by: Kumar Kartikeya Dwivedi --- .../bpf/prog_tests/test_struct_ops_nullable.c | 43 ++++++++++++++++++ .../selftests/bpf/progs/struct_ops_nullable.c | 45 +++++++++++++++++++ .../bpf/progs/struct_ops_nullable_fail.c | 28 ++++++++++++ .../selftests/bpf/test_kmods/bpf_testmod.c | 33 ++++++++++++++ .../selftests/bpf/test_kmods/bpf_testmod.h | 15 +++++++ .../bpf/test_kmods/bpf_testmod_kfunc.h | 1 + 6 files changed, 165 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_nullable.c create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_nullable.c create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_nullable_fail.c diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_nullable.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_nullable.c new file mode 100644 index 000000000000..fc52870782b7 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_nullable.c @@ -0,0 +1,43 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ +#include + +#include "struct_ops_nullable.skel.h" +#include "struct_ops_nullable_fail.skel.h" + +/* + * Attach a callback that gets a trusted and a trusted __nullable task pointer + * through its argument struct and drive it through the + * bpf_testmod_ops3_call_test_nullable() kfunc. + */ +static void nullable_member(void) +{ + LIBBPF_OPTS(bpf_test_run_opts, topts); + struct struct_ops_nullable *skel; + struct bpf_link *link; + int err; + + skel = struct_ops_nullable__open_and_load(); + if (!ASSERT_OK_PTR(skel, "struct_ops_nullable__open_and_load")) + return; + + link = bpf_map__attach_struct_ops(skel->maps.testmod_nullable); + if (!ASSERT_OK_PTR(link, "attach_struct_ops")) + goto out; + + err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.trigger), &topts); + ASSERT_OK(err, "test_run"); + ASSERT_EQ(topts.retval, 0, "trigger_retval"); + + bpf_link__destroy(link); +out: + struct_ops_nullable__destroy(skel); +} + +/* Serialized because it attaches the singleton bpf_testmod_ops3. */ +void serial_test_struct_ops_nullable(void) +{ + if (test__start_subtest("nullable_member")) + nullable_member(); + RUN_TESTS(struct_ops_nullable_fail); +} diff --git a/tools/testing/selftests/bpf/progs/struct_ops_nullable.c b/tools/testing/selftests/bpf/progs/struct_ops_nullable.c new file mode 100644 index 000000000000..387792924c09 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/struct_ops_nullable.c @@ -0,0 +1,45 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ + +#include +#include +#include +#include "../test_kmods/bpf_testmod.h" +#include "../test_kmods/bpf_testmod_kfunc.h" + +char _license[] SEC("license") = "GPL"; + +SEC("struct_ops/test_nullable") +int BPF_PROG(test_nullable_cb, struct bpf_testmod_nullable_args *args) +{ + struct task_struct *t; + int ret = 0; + + /* trusted, so good for a kfunc as is */ + t = bpf_task_acquire(args->task); + if (!t) + return -1; + bpf_task_release(t); + + /* trusted but __nullable, so a check has to come first */ + if (args->task_or_null) { + t = bpf_task_acquire(args->task_or_null); + if (!t) + return -1; + bpf_task_release(t); + ret = 1; + } + return ret; +} + +SEC(".struct_ops.link") +struct bpf_testmod_ops3 testmod_nullable = { + .test_nullable = (void *)test_nullable_cb, +}; + +SEC("syscall") +int trigger(void *ctx) +{ + /* one call without task_or_null, one with */ + return bpf_testmod_ops3_call_test_nullable() != 2; +} diff --git a/tools/testing/selftests/bpf/progs/struct_ops_nullable_fail.c b/tools/testing/selftests/bpf/progs/struct_ops_nullable_fail.c new file mode 100644 index 000000000000..c15b3a8c8d39 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/struct_ops_nullable_fail.c @@ -0,0 +1,28 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ + +#include +#include +#include +#include "bpf_misc.h" +#include "../test_kmods/bpf_testmod.h" + +char _license[] SEC("license") = "GPL"; + +/* The member is trusted, but __nullable, so it needs a check before the kfunc. */ +SEC("struct_ops/test_nullable") +__failure __msg("Possibly NULL pointer passed to trusted") +int BPF_PROG(unchecked_nullable, struct bpf_testmod_nullable_args *args) +{ + struct task_struct *t; + + t = bpf_task_acquire(args->task_or_null); + if (t) + bpf_task_release(t); + return 0; +} + +SEC(".struct_ops.link") +struct bpf_testmod_ops3 testmod_nullable_fail = { + .test_nullable = (void *)unchecked_nullable, +}; diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c index b4f0af2aeca4..0c0152885da3 100644 --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c @@ -460,6 +460,11 @@ static int bpf_testmod_ops3__test_arena_multislot(struct bpf_testmod_arena_pair return 0; } +static int bpf_testmod_ops3__test_nullable(struct bpf_testmod_nullable_args *args) +{ + return 0; +} + static struct bpf_testmod_ops3 __bpf_testmod_ops3 = { .test_1 = bpf_testmod_test_3, .test_2 = bpf_testmod_test_4, @@ -467,6 +472,7 @@ static struct bpf_testmod_ops3 __bpf_testmod_ops3 = { .test_arena_nullable = bpf_testmod_ops3__test_arena_nullable, .test_arena_stack = bpf_testmod_ops3__test_arena_stack, .test_arena_multislot = bpf_testmod_ops3__test_arena_multislot, + .test_nullable = bpf_testmod_ops3__test_nullable, }; static void bpf_testmod_test_struct_ops3(void) @@ -507,6 +513,32 @@ __bpf_kfunc int bpf_testmod_ops3_call_test_arena_multislot(u64 *ptr__arena) return st_ops3->test_arena_multislot(p, ptr__arena); } +/* + * The members of struct bpf_testmod_nullable_args are trusted the way the + * verifier's BTF_TYPE_SAFE_TRUSTED() lists vmlinux members: through a struct + * of the same name with the __safe_trusted suffix in the BTF of the module. + */ +struct bpf_testmod_nullable_args__safe_trusted { + struct task_struct *task; + struct task_struct *task_or_null; +}; + +/* + * Call test_nullable() with @task_or_null unset, then set. The callback + * returns 1 when it found a task there, so the expected result is 2. + */ +__bpf_kfunc int bpf_testmod_ops3_call_test_nullable(void) +{ + struct bpf_testmod_nullable_args args = { .task = current }; + int ret; + + BTF_TYPE_EMIT(struct bpf_testmod_nullable_args__safe_trusted); + + ret = st_ops3->test_nullable(&args); + args.task_or_null = current; + return ret | st_ops3->test_nullable(&args) << 1; +} + struct bpf_testmod_btf_type_tag_1 { int a; }; @@ -926,6 +958,7 @@ BTF_ID_FLAGS(func, bpf_testmod_ops3_call_test_arena) BTF_ID_FLAGS(func, bpf_testmod_ops3_call_test_arena_nullable) BTF_ID_FLAGS(func, bpf_testmod_ops3_call_test_arena_stack) BTF_ID_FLAGS(func, bpf_testmod_ops3_call_test_arena_multislot) +BTF_ID_FLAGS(func, bpf_testmod_ops3_call_test_nullable) BTF_ID_FLAGS(func, bpf_kfunc_get_default_trusted_ptr_test); BTF_ID_FLAGS(func, bpf_kfunc_put_default_trusted_ptr_test); BTF_ID_FLAGS(func, bpf_kfunc_kasan_poison) diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.h b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.h index 2b12f81bf748..b905c35490eb 100644 --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.h +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.h @@ -114,6 +114,19 @@ struct bpf_testmod_arena_pair { u64 b; }; +/* The kernel defines the BPF pointer qualifiers, user space and BPF programs need them empty. */ +#ifndef __nullable +#define __nullable +#endif + +/* Arguments of test_nullable(), trusted through the __safe_trusted alias in the module */ +struct bpf_testmod_nullable_args { + /* never NULL */ + struct task_struct *task; + /* NULL on the first call, set on the second */ + struct task_struct __nullable *task_or_null; +}; + struct bpf_testmod_ops3 { int (*test_1)(void); int (*test_2)(void); @@ -125,6 +138,8 @@ struct bpf_testmod_ops3 { u64 g, u64 h, u64 *ptr); /* a multi-slot leading arg, so @ptr is not at the slot its arg index suggests */ int (*test_arena_multislot)(struct bpf_testmod_arena_pair p, u64 *ptr); + /* Used to test __nullable pointer members. */ + int (*test_nullable)(struct bpf_testmod_nullable_args *args); }; struct st_ops_args { diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h index 67c02a421d13..d88c99109c31 100644 --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod_kfunc.h @@ -218,6 +218,7 @@ int bpf_testmod_ops3_call_test_arena(__u64 *ptr__arena) __ksym; int bpf_testmod_ops3_call_test_arena_nullable(__u64 *ptr__arena__nullable) __ksym; int bpf_testmod_ops3_call_test_arena_stack(__u64 *ptr__arena) __ksym; int bpf_testmod_ops3_call_test_arena_multislot(__u64 *ptr__arena) __ksym; +int bpf_testmod_ops3_call_test_nullable(void) __ksym; __u64 bpf_kfunc_call_test1(struct sock *sk, __u32 a, __u64 b, __u32 c, __u64 d) __ksym; -- 2.53.0-Meta