* [PATCH bpf-next v4 1/2] bpf: Reject sleepable kprobe_multi programs at attach time
2026-04-08 18:35 [PATCH bpf-next v4 0/2] Reject sleepable kprobe_multi programs at attach time Varun R Mallya
@ 2026-04-08 18:35 ` Varun R Mallya
2026-04-08 18:35 ` [PATCH bpf-next v4 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Varun R Mallya
1 sibling, 0 replies; 5+ messages in thread
From: Varun R Mallya @ 2026-04-08 18:35 UTC (permalink / raw)
To: bpf, leon.hwang, memxor, jolsa
Cc: ast, daniel, yonghong.song, rostedt, 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>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
Acked-by: Jiri Olsa <jolsa@kernel.org>
---
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] 5+ messages in thread* [PATCH bpf-next v4 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable
2026-04-08 18:35 [PATCH bpf-next v4 0/2] Reject sleepable kprobe_multi programs at attach time Varun R Mallya
2026-04-08 18:35 ` [PATCH bpf-next v4 1/2] bpf: " Varun R Mallya
@ 2026-04-08 18:35 ` Varun R Mallya
2026-04-08 18:47 ` Varun R Mallya
1 sibling, 1 reply; 5+ messages in thread
From: Varun R Mallya @ 2026-04-08 18:35 UTC (permalink / raw)
To: bpf, leon.hwang, memxor, jolsa
Cc: ast, daniel, yonghong.song, rostedt, 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.
Suggested-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
---
.../bpf/prog_tests/kprobe_multi_test.c | 78 ++++++++++++++++++-
.../bpf/progs/kprobe_multi_sleepable.c | 25 ++++++
2 files changed, 102 insertions(+), 1 deletion(-)
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..e4f9021a84ed 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"
@@ -220,7 +221,9 @@ static void test_attach_api_syms(void)
static void test_attach_api_fails(void)
{
LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
+ LIBBPF_OPTS(bpf_test_run_opts, topts);
struct kprobe_multi *skel = NULL;
+ struct kprobe_multi_sleepable *sl_skel = NULL;
struct bpf_link *link = NULL;
unsigned long long addrs[2];
const char *syms[2] = {
@@ -228,7 +231,7 @@ static void test_attach_api_fails(void)
"bpf_fentry_test2",
};
__u64 cookies[2];
- int saved_error;
+ int saved_error, err;
addrs[0] = ksym_get_addr("bpf_fentry_test1");
addrs[1] = ksym_get_addr("bpf_fentry_test2");
@@ -351,9 +354,39 @@ static void test_attach_api_fails(void)
if (!ASSERT_EQ(saved_error, -ENOENT, "fail_8_error"))
goto cleanup;
+ /* fail_9 - sleepable kprobe multi should not attach */
+ sl_skel = kprobe_multi_sleepable__open();
+ if (!ASSERT_OK_PTR(sl_skel, "sleep_skel_open"))
+ goto cleanup;
+
+ sl_skel->bss->user_ptr = sl_skel;
+
+ err = bpf_program__set_flags(sl_skel->progs.handle_kprobe_multi_sleepable,
+ BPF_F_SLEEPABLE);
+ if (!ASSERT_OK(err, "sleep_skel_set_flags"))
+ goto cleanup;
+
+ err = kprobe_multi_sleepable__load(sl_skel);
+ if (!ASSERT_OK(err, "sleep_skel_load"))
+ goto cleanup;
+
+ link = bpf_program__attach_kprobe_multi_opts(sl_skel->progs.handle_kprobe_multi_sleepable,
+ "bpf_fentry_test1", NULL);
+ saved_error = -errno;
+
+ if (!ASSERT_ERR_PTR(link, "fail_9"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(saved_error, -EINVAL, "fail_9_error"))
+ goto cleanup;
+
+ err = bpf_prog_test_run_opts(bpf_program__fd(sl_skel->progs.fentry), &topts);
+ ASSERT_OK(err, "bpf_prog_test_run_opts");
+
cleanup:
bpf_link__destroy(link);
kprobe_multi__destroy(skel);
+ kprobe_multi_sleepable__destroy(sl_skel);
}
static void test_session_skel_api(void)
@@ -609,6 +642,47 @@ static void test_override(void)
kprobe_multi_override__destroy(skel);
}
+static void test_attach_multi_sleepable(void)
+{
+ struct kprobe_multi_sleepable *skel;
+ int err;
+
+ LIBBPF_OPTS(bpf_test_run_opts, topts);
+
+ 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;
+
+ skel->links.handle_kprobe_multi_sleepable =
+ bpf_program__attach_kprobe_multi_opts(skel->progs.handle_kprobe_multi_sleepable,
+ "bpf_fentry_test1", NULL);
+
+ ASSERT_EQ(libbpf_get_error(skel->links.handle_kprobe_multi_sleepable),
+ -EINVAL, "attach_multi_sleepable_err");
+
+ ASSERT_ERR_PTR(skel->links.handle_kprobe_multi_sleepable,
+ "bpf_program__attach_kprobe_multi_opts");
+
+ 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);
+}
+
#ifdef __x86_64__
static void test_attach_write_ctx(void)
{
@@ -676,5 +750,7 @@ 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";
--
2.53.0
^ permalink raw reply related [flat|nested] 5+ messages in thread