Re: [PATCH bpf v2] bpf: Reject sleepable kprobe_multi programs at attach time

[Kumar Kartikeya Dwivedi]

On Wed, 1 Apr 2026 at 18:26, Varun R Mallya <varunrmallya@xxxxxxxxx> wrote:
>
> kprobe.multi programs run in atomic/RCU context and cannot sleep.
> However, bpf_kprobe_multi_link_attach() did not validate whether the
> program being attached had the sleepable flag set, allowing sleepable
> helpers such as bpf_copy_from_user() to be invoked from a non-sleepable
> context.
>
> This causes a "sleeping function called from invalid context" splat:
>
>   BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169
>   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo
>   preempt_count: 1, expected: 0
>   RCU nest depth: 2, expected: 0
>
> Fix this by rejecting sleepable programs early in
> bpf_kprobe_multi_link_attach(), before any further processing.
>
> Also add a selftest that tries to load a sleepable kprobe_multi program
> and it needs to be rejected for the test to pass.
>
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Varun R Mallya <varunrmallya@xxxxxxxxx>
> ---

Looks ok, but please split kernel fix and tests into separate patches,
and no need to reply to this thread.

pw-bot: cr


>  kernel/trace/bpf_trace.c                      |  4 ++
>  .../bpf/prog_tests/kprobe_multi_test.c        | 41 +++++++++++++++++++
>  .../bpf/progs/kprobe_multi_sleepable.c        | 13 ++++++
>  3 files changed, 58 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0b040a417442..af7079aa0f36 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>         if (!is_kprobe_multi(prog))
>                 return -EINVAL;
>
> +       /* kprobe_multi is not allowed to be sleepable. */
> +       if (prog->sleepable)
> +               return -EINVAL;
> +
>         /* Writing to context is not allowed for kprobes. */
>         if (prog->aux->kprobe_write_ctx)
>                 return -EINVAL;
> diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> index 78c974d4ea33..f02fec2b6fda 100644
> --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> @@ -10,6 +10,7 @@
>  #include "kprobe_multi_session_cookie.skel.h"
>  #include "kprobe_multi_verifier.skel.h"
>  #include "kprobe_write_ctx.skel.h"
> +#include "kprobe_multi_sleepable.skel.h"
>  #include "bpf/libbpf_internal.h"
>  #include "bpf/hashmap.h"
>
> @@ -633,6 +634,44 @@ static void test_attach_write_ctx(void)
>  }
>  #endif
>
> +static void test_attach_multi_sleepable(void)
> +{
> +       struct kprobe_multi_sleepable *skel;
> +       int err;
> +
> +       skel = kprobe_multi_sleepable__open();
> +       if (!ASSERT_OK_PTR(skel, "kprobe_multi_sleepable__open"))
> +               return;
> +
> +       err = bpf_program__set_flags(skel->progs.handle_kprobe_multi_sleepable,
> +                                    BPF_F_SLEEPABLE);
> +       if (!ASSERT_OK(err, "bpf_program__set_flags"))
> +               goto cleanup;
> +
> +       /* Load should succeed even with BPF_F_SLEEPABLE for KPROBE types */
> +       err = kprobe_multi_sleepable__load(skel);
> +       if (!ASSERT_OK(err, "kprobe_multi_sleepable__load"))
> +               goto cleanup;
> +
> +       /* Attachment must fail for kprobe.multi + BPF_F_SLEEPABLE.
> +        * Also chosen a stable symbol to send into opts
> +        */
> +       LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
> +       const char *sym = "vfs_read";
> +
> +       opts.syms = &sym;
> +       opts.cnt = 1;
> +
> +       skel->links.handle_kprobe_multi_sleepable =
> +               bpf_program__attach_kprobe_multi_opts(skel->progs.handle_kprobe_multi_sleepable,
> +                                                     NULL, &opts);
> +       ASSERT_ERR_PTR(skel->links.handle_kprobe_multi_sleepable,
> +                      "bpf_program__attach_kprobe_multi_opts");
> +
> +cleanup:
> +       kprobe_multi_sleepable__destroy(skel);
> +}
> +
>  void serial_test_kprobe_multi_bench_attach(void)
>  {
>         if (test__start_subtest("kernel"))
> @@ -676,5 +715,7 @@ void test_kprobe_multi_test(void)
>                 test_unique_match();
>         if (test__start_subtest("attach_write_ctx"))
>                 test_attach_write_ctx();
> +       if (test__start_subtest("attach_multi_sleepable"))
> +               test_attach_multi_sleepable();
>         RUN_TESTS(kprobe_multi_verifier);
>  }
> diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
> new file mode 100644
> index 000000000000..56973ad8779d
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
> @@ -0,0 +1,13 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +SEC("kprobe.multi")
> +int handle_kprobe_multi_sleepable(struct pt_regs *ctx)
> +{
> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.53.0
>