* [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time
@ 2026-04-01 19:11 Varun R Mallya
2026-04-01 19:11 ` [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
` (4 more replies)
0 siblings, 5 replies; 10+ messages in thread
From: Varun R Mallya @ 2026-04-01 19:11 UTC (permalink / raw)
To: bpf
Cc: ast, daniel, memxor, yonghong.song, jolsa, rostedt, mhiramat,
linux-kernel, linux-trace-kernel, varunrmallya
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.
Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
---
kernel/trace/bpf_trace.c | 4 ++++
1 file changed, 4 insertions(+)
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;
--
2.53.0
^ permalink raw reply related [flat|nested] 10+ messages in thread
* [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
2026-04-01 19:11 [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Varun R Mallya
@ 2026-04-01 19:11 ` Varun R Mallya
2026-04-01 22:50 ` Kumar Kartikeya Dwivedi
2026-04-02 4:13 ` Leon Hwang
2026-04-01 22:45 ` [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Kumar Kartikeya Dwivedi
` (3 subsequent siblings)
4 siblings, 2 replies; 10+ messages in thread
From: Varun R Mallya @ 2026-04-01 19:11 UTC (permalink / raw)
To: bpf
Cc: ast, daniel, memxor, yonghong.song, jolsa, rostedt, mhiramat,
linux-kernel, linux-trace-kernel, varunrmallya
Add a selftest to ensure that kprobe_multi programs cannot be attached
using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
---
.../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++
.../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++
2 files changed, 54 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
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
^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time
2026-04-01 19:11 [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Varun R Mallya
2026-04-01 19:11 ` [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
@ 2026-04-01 22:45 ` Kumar Kartikeya Dwivedi
2026-04-02 4:13 ` Leon Hwang
` (2 subsequent siblings)
4 siblings, 0 replies; 10+ messages in thread
From: Kumar Kartikeya Dwivedi @ 2026-04-01 22:45 UTC (permalink / raw)
To: Varun R Mallya, Jiri Olsa
Cc: bpf, ast, daniel, yonghong.song, rostedt, mhiramat, linux-kernel,
linux-trace-kernel
On Wed, 1 Apr 2026 at 21:11, Varun R Mallya <varunrmallya@gmail.com> 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.
>
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> ---
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Jiri, would be great if you can ack both patches too.
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
2026-04-01 19:11 ` [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
@ 2026-04-01 22:50 ` Kumar Kartikeya Dwivedi
2026-04-02 9:46 ` Jiri Olsa
2026-04-02 4:13 ` Leon Hwang
1 sibling, 1 reply; 10+ messages in thread
From: Kumar Kartikeya Dwivedi @ 2026-04-01 22:50 UTC (permalink / raw)
To: Varun R Mallya
Cc: bpf, ast, daniel, yonghong.song, jolsa, rostedt, mhiramat,
linux-kernel, linux-trace-kernel
On Wed, 1 Apr 2026 at 21:11, Varun R Mallya <varunrmallya@gmail.com> wrote:
>
> Add a selftest to ensure that kprobe_multi programs cannot be attached
> using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
> rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.
>
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> ---
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> .../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++
> .../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++
> 2 files changed, 54 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
>
> 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");
Nit: While vfs_read will likely remain stable, the check could
probably be stronger to distinguish an attach error from -EINVAL?
I added a typo to vfs_read and it still passed, because it failed to
attach instead of getting rejected on unfixed kernel.
May not be a big deal since vfs_read is unlikely to break.
I verified it works by adding bpf_copy_from_user to the program and
attaching to SYS_PREFIX sys_getpid and invoking the splat though, so
LGTM otherwise.
> +
> +cleanup:
> + kprobe_multi_sleepable__destroy(skel);
> +}
> +
> [...]
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time
2026-04-01 19:11 [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Varun R Mallya
2026-04-01 19:11 ` [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
2026-04-01 22:45 ` [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Kumar Kartikeya Dwivedi
@ 2026-04-02 4:13 ` Leon Hwang
2026-04-02 9:47 ` Jiri Olsa
2026-04-02 16:50 ` patchwork-bot+netdevbpf
4 siblings, 0 replies; 10+ messages in thread
From: Leon Hwang @ 2026-04-02 4:13 UTC (permalink / raw)
To: Varun R Mallya, bpf
Cc: ast, daniel, memxor, yonghong.song, jolsa, rostedt, mhiramat,
linux-kernel, linux-trace-kernel
On 2/4/26 03:11, Varun R Mallya 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.
>
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
The cover letter is missing, and the change logs are missing, too.
[...]
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
2026-04-01 19:11 ` [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
2026-04-01 22:50 ` Kumar Kartikeya Dwivedi
@ 2026-04-02 4:13 ` Leon Hwang
1 sibling, 0 replies; 10+ messages in thread
From: Leon Hwang @ 2026-04-02 4:13 UTC (permalink / raw)
To: Varun R Mallya, bpf
Cc: ast, daniel, memxor, yonghong.song, jolsa, rostedt, mhiramat,
linux-kernel, linux-trace-kernel
Above all, I think the test should reproduce the BUG without the fix.
I update the test to reproduce the BUG, then verify that the BUG will be
rejected with the fix.
The updated test is attached at last.
On 2/4/26 03:11, Varun R Mallya wrote:
> Add a selftest to ensure that kprobe_multi programs cannot be attached
> using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
> rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.
>
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> ---
> .../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++
> .../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++
> 2 files changed, 54 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
>
> 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";
They should stay with skel and err. See below.
> +
> + 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");
As Kumar suggested, better to also verify the error here.
ASSERT_EQ(libbpf_get_error(skel->links.handle_kprobe_multi_sleepable),
-EINVAL,
"bpf_program__attach_kprobe_multi_opts error");
> +
> +cleanup:
> + kprobe_multi_sleepable__destroy(skel);
> +}
> +
[...]
Thanks,
Leon
---
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..d59cf840da83 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 +634,52 @@ static void test_attach_write_ctx(void)
}
#endif
+static void test_attach_multi_sleepable(void)
+{
+ struct kprobe_multi_sleepable *skel;
+ const char *sym = "bpf_fentry_test1";
+ int err;
+ LIBBPF_OPTS(bpf_test_run_opts, topts);
+ LIBBPF_OPTS(bpf_kprobe_multi_opts, opts,
+ .syms = &sym,
+ .cnt = 1
+ );
+
+ skel = kprobe_multi_sleepable__open();
+ if (!ASSERT_OK_PTR(skel, "kprobe_multi_sleepable__open"))
+ return;
+
+ skel->bss->user_ptr = skel;
+
+ 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
+ */
+ 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");
+
ASSERT_EQ(libbpf_get_error(skel->links.handle_kprobe_multi_sleepable),
-EINVAL,
+ "attach_multi_sleepable_err");
+
+ err =
bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry), &topts);
+ ASSERT_OK(err, "bpf_prog_test_run_opts");
+
+cleanup:
+ kprobe_multi_sleepable__destroy(skel);
+}
+
void serial_test_kprobe_multi_bench_attach(void)
{
if (test__start_subtest("kernel"))
@@ -676,5 +723,7 @@ 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..932e1d9c72e2
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+void *user_ptr = 0;
+
+SEC("kprobe.multi")
+int handle_kprobe_multi_sleepable(struct pt_regs *ctx)
+{
+ int a, err;
+
+ err = bpf_copy_from_user(&a, sizeof(a), user_ptr);
+ barrier_var(a);
+ return err;
+}
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(fentry)
+{
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";
^ permalink raw reply related [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
2026-04-01 22:50 ` Kumar Kartikeya Dwivedi
@ 2026-04-02 9:46 ` Jiri Olsa
2026-04-06 20:11 ` Kumar Kartikeya Dwivedi
0 siblings, 1 reply; 10+ messages in thread
From: Jiri Olsa @ 2026-04-02 9:46 UTC (permalink / raw)
To: Kumar Kartikeya Dwivedi
Cc: Varun R Mallya, bpf, ast, daniel, yonghong.song, rostedt,
mhiramat, linux-kernel, linux-trace-kernel
On Thu, Apr 02, 2026 at 12:50:10AM +0200, Kumar Kartikeya Dwivedi wrote:
> On Wed, 1 Apr 2026 at 21:11, Varun R Mallya <varunrmallya@gmail.com> wrote:
> >
> > Add a selftest to ensure that kprobe_multi programs cannot be attached
> > using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
> > rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.
> >
> > Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> > ---
>
> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
>
> > .../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++
> > .../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++
> > 2 files changed, 54 insertions(+)
> > create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
> >
> > 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");
>
> Nit: While vfs_read will likely remain stable, the check could
> probably be stronger to distinguish an attach error from -EINVAL?
> I added a typo to vfs_read and it still passed, because it failed to
> attach instead of getting rejected on unfixed kernel.
> May not be a big deal since vfs_read is unlikely to break.
> I verified it works by adding bpf_copy_from_user to the program and
> attaching to SYS_PREFIX sys_getpid and invoking the splat though, so
> LGTM otherwise.
why not use bpf_fentry_test2 ? you could also put it in pattern argument
and bypass opts completely (up to you)
also there's test_attach_api_fails test, please move it over there
thanks,
jirka
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time
2026-04-01 19:11 [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Varun R Mallya
` (2 preceding siblings ...)
2026-04-02 4:13 ` Leon Hwang
@ 2026-04-02 9:47 ` Jiri Olsa
2026-04-02 16:50 ` patchwork-bot+netdevbpf
4 siblings, 0 replies; 10+ messages in thread
From: Jiri Olsa @ 2026-04-02 9:47 UTC (permalink / raw)
To: Varun R Mallya
Cc: bpf, ast, daniel, memxor, yonghong.song, rostedt, mhiramat,
linux-kernel, linux-trace-kernel
On Thu, Apr 02, 2026 at 12:41:25AM +0530, Varun R Mallya 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.
>
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
nice catch!
Acked-by: Jiri Olsa <jolsa@kernel.org>
thanks,
jirka
> ---
> kernel/trace/bpf_trace.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> 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;
> --
> 2.53.0
>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time
2026-04-01 19:11 [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Varun R Mallya
` (3 preceding siblings ...)
2026-04-02 9:47 ` Jiri Olsa
@ 2026-04-02 16:50 ` patchwork-bot+netdevbpf
4 siblings, 0 replies; 10+ messages in thread
From: patchwork-bot+netdevbpf @ 2026-04-02 16:50 UTC (permalink / raw)
To: Varun R Mallya
Cc: bpf, ast, daniel, memxor, yonghong.song, jolsa, rostedt, mhiramat,
linux-kernel, linux-trace-kernel
Hello:
This series was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:
On Thu, 2 Apr 2026 00:41:25 +0530 you 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:
>
> [...]
Here is the summary with links:
- [bpf,v3,1/2] bpf: Reject sleepable kprobe_multi programs at attach time
https://git.kernel.org/bpf/bpf/c/eb7024bfcc5f
- [bpf,v3,2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
(no matching commit)
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
2026-04-02 9:46 ` Jiri Olsa
@ 2026-04-06 20:11 ` Kumar Kartikeya Dwivedi
0 siblings, 0 replies; 10+ messages in thread
From: Kumar Kartikeya Dwivedi @ 2026-04-06 20:11 UTC (permalink / raw)
To: Jiri Olsa
Cc: Varun R Mallya, bpf, ast, daniel, yonghong.song, rostedt,
mhiramat, linux-kernel, linux-trace-kernel
On Thu, 2 Apr 2026 at 11:46, Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Thu, Apr 02, 2026 at 12:50:10AM +0200, Kumar Kartikeya Dwivedi wrote:
> > On Wed, 1 Apr 2026 at 21:11, Varun R Mallya <varunrmallya@gmail.com> wrote:
> > >
> > > Add a selftest to ensure that kprobe_multi programs cannot be attached
> > > using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
> > > rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.
> > >
> > > Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> > > ---
> >
> > Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> >
> > > .../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++
> > > .../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++
> > > 2 files changed, 54 insertions(+)
> > > create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
> > >
> > > 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");
> >
> > Nit: While vfs_read will likely remain stable, the check could
> > probably be stronger to distinguish an attach error from -EINVAL?
> > I added a typo to vfs_read and it still passed, because it failed to
> > attach instead of getting rejected on unfixed kernel.
> > May not be a big deal since vfs_read is unlikely to break.
> > I verified it works by adding bpf_copy_from_user to the program and
> > attaching to SYS_PREFIX sys_getpid and invoking the splat though, so
> > LGTM otherwise.
>
> why not use bpf_fentry_test2 ? you could also put it in pattern argument
> and bypass opts completely (up to you)
>
> also there's test_attach_api_fails test, please move it over there
>
Varun, the selftest is still not applied, only the fix. Please follow
up and target bpf-next tree this time.
Thanks.
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2026-04-06 20:12 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
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2026-04-01 19:11 [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Varun R Mallya
2026-04-01 19:11 ` [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
2026-04-01 22:50 ` Kumar Kartikeya Dwivedi
2026-04-02 9:46 ` Jiri Olsa
2026-04-06 20:11 ` Kumar Kartikeya Dwivedi
2026-04-02 4:13 ` Leon Hwang
2026-04-01 22:45 ` [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Kumar Kartikeya Dwivedi
2026-04-02 4:13 ` Leon Hwang
2026-04-02 9:47 ` Jiri Olsa
2026-04-02 16:50 ` patchwork-bot+netdevbpf
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