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Wed, 08 Apr 2026 12:02:18 -0700 (PDT) From: Varun R Mallya To: bpf@vger.kernel.org, leon.hwang@linux.dev, memxor@gmail.com, jolsa@kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, yonghong.song@linux.dev, rostedt@goodmis.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, varunrmallya@gmail.com Subject: [PATCH bpf-next v5 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Date: Thu, 9 Apr 2026 00:31:36 +0530 Message-ID: <20260408190137.101418-2-varunrmallya@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408190137.101418-1-varunrmallya@gmail.com> References: <20260408190137.101418-1-varunrmallya@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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/uac= cess.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 Acked-by: Kumar Kartikeya Dwivedi Acked-by: Leon Hwang Acked-by: Jiri Olsa --- 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_att= r *attr, struct bpf_prog *pr if (!is_kprobe_multi(prog)) return -EINVAL; =20 + /* 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; --=20 2.53.0 From nobody Mon Jun 15 07:33:53 2026 Received: from mail-pj1-f52.google.com (mail-pj1-f52.google.com [209.85.216.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 083C83D9DB2 for ; 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Wed, 08 Apr 2026 12:02:25 -0700 (PDT) Received: from computer.goose-salary.ts.net ([2a09:bac5:40b2:1a96::2a6:4e]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35e34d0d9efsm143630a91.8.2026.04.08.12.02.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2026 12:02:24 -0700 (PDT) From: Varun R Mallya To: bpf@vger.kernel.org, leon.hwang@linux.dev, memxor@gmail.com, jolsa@kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, yonghong.song@linux.dev, rostedt@goodmis.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, varunrmallya@gmail.com Subject: [PATCH bpf-next v5 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable Date: Thu, 9 Apr 2026 00:31:37 +0530 Message-ID: <20260408190137.101418-3-varunrmallya@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408190137.101418-1-varunrmallya@gmail.com> References: <20260408190137.101418-1-varunrmallya@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Signed-off-by: Varun R Mallya --- .../bpf/prog_tests/kprobe_multi_test.c | 35 ++++++++++++++++++- .../bpf/progs/kprobe_multi_sleepable.c | 25 +++++++++++++ 2 files changed, 59 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepabl= e.c diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/t= ools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c index 78c974d4ea33..a07cd853ed2a 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" =20 @@ -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 =3D NULL; + struct kprobe_multi_sleepable *sl_skel =3D NULL; struct bpf_link *link =3D NULL; unsigned long long addrs[2]; const char *syms[2] =3D { @@ -228,7 +231,7 @@ static void test_attach_api_fails(void) "bpf_fentry_test2", }; __u64 cookies[2]; - int saved_error; + int saved_error, err; =20 addrs[0] =3D ksym_get_addr("bpf_fentry_test1"); addrs[1] =3D 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; =20 + /* fail_9 - sleepable kprobe multi should not attach */ + sl_skel =3D kprobe_multi_sleepable__open(); + if (!ASSERT_OK_PTR(sl_skel, "sleep_skel_open")) + goto cleanup; + + sl_skel->bss->user_ptr =3D sl_skel; + + err =3D bpf_program__set_flags(sl_skel->progs.handle_kprobe_multi_sleepab= le, + BPF_F_SLEEPABLE); + if (!ASSERT_OK(err, "sleep_skel_set_flags")) + goto cleanup; + + err =3D kprobe_multi_sleepable__load(sl_skel); + if (!ASSERT_OK(err, "sleep_skel_load")) + goto cleanup; + + link =3D bpf_program__attach_kprobe_multi_opts(sl_skel->progs.handle_kpro= be_multi_sleepable, + "bpf_fentry_test1", NULL); + saved_error =3D -errno; + + if (!ASSERT_ERR_PTR(link, "fail_9")) + goto cleanup; + + if (!ASSERT_EQ(saved_error, -EINVAL, "fail_9_error")) + goto cleanup; + + err =3D bpf_prog_test_run_opts(bpf_program__fd(sl_skel->progs.fentry), &t= opts); + ASSERT_OK(err, "bpf_prog_test_run_opts"); + cleanup: bpf_link__destroy(link); kprobe_multi__destroy(skel); + kprobe_multi_sleepable__destroy(sl_skel); } =20 static void test_session_skel_api(void) diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c b/t= ools/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 +#include + +void *user_ptr =3D 0; + +SEC("kprobe.multi") +int handle_kprobe_multi_sleepable(struct pt_regs *ctx) +{ + int a, err; + + err =3D 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") =3D "GPL"; --=20 2.53.0