From nobody Thu Apr 2 20:28:05 2026 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0DFC03A3821 for ; Thu, 26 Mar 2026 14:17:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774534676; cv=none; b=eLLjlaRpuqSVNuBtNt22tq2fsd+lBaeF3SbDKLFlKc9BNR7IH01BenVFQk/NMtgvbBU1iS1GVRBe0UQKe1tFBOFbC6jKlfeRElwRYqU+GCthCMDNw4KyRUBQ3SdGBtL9Q7jJLR+qKRTuzBYTFJ7DAYFxBa6FqaSqralU0nL0Nsw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774534676; c=relaxed/simple; bh=WVbCpWwtXFS5WnRF1GNs4kUcVMd1qblCOHqrZ/DEfCo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dov8FssDbSmC7kebt6YygaKNjFvnuV5/iU+tfOLfzteHfozZMzD1fldyaefPcINAPjMuqfhfYvwt3hK/K+UqTjUsn9tbtPxIq8N1lc36OrFgR9giQh7CzlpHxI4IpjbLZBhfr0MfEusF7roMZLvYLOpXRGOU/Ocl8Di1K+QGY1I= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=aEK53iSg; arc=none smtp.client-ip=95.215.58.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="aEK53iSg" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774534667; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+Ni2FOm+AKZAFdBlcw1DzXopDy53nnYWg3V8M/1f2/Q=; b=aEK53iSgYB1Xg0JVyrEQW2Mb6yMvIXx15VjUa1ek/QwIXZsmsGqU5mwLDHuBxcMKvf6Dz5 seBxe7IpoUCxpR0LKtZiYJhCzP4ABDYUmJj++GuoXFm2X+MU3MKC6TXwNQnDH4ayw6jEUK EeR5mvfLkiDND3WTAerNwfM2q4xJoQY= From: Leon Hwang To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Shuah Khan , Feng Yang , Leon Hwang , Toke Hoiland-Jorgensen , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-patches-bot@fb.com Subject: [PATCH bpf-next v2 1/2] bpf: Fix abuse of kprobe_write_ctx via freplace Date: Thu, 26 Mar 2026 22:17:17 +0800 Message-ID: <20260326141718.17731-2-leon.hwang@linux.dev> In-Reply-To: <20260326141718.17731-1-leon.hwang@linux.dev> References: <20260326141718.17731-1-leon.hwang@linux.dev> 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 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" uprobe programs are allowed to modify struct pt_regs. Since the actual program type of uprobe is KPROBE, it can be abused to modify struct pt_regs via kprobe+freplace when the kprobe attaches to kernel functions. For example, SEC("?kprobe") int kprobe(struct pt_regs *regs) { return 0; } SEC("?freplace") int freplace_kprobe(struct pt_regs *regs) { regs->di =3D 0; return 0; } freplace_kprobe prog will attach to kprobe prog. kprobe prog will attach to a kernel function. Without this patch, when the kernel function runs, its first arg will always be set as 0 via the freplace_kprobe prog. To fix the abuse of kprobe_write_ctx=3Dtrue via kprobe+freplace, disallow attaching freplace programs on kprobe programs with different kprobe_write_ctx values. Fixes: 7384893d970e ("bpf: Allow uprobe program to change context registers= ") Signed-off-by: Leon Hwang Acked-by: Jiri Olsa Acked-by: Song Liu --- kernel/bpf/syscall.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 51ade3cde8bb..1dd2ea076d8b 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3733,6 +3733,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *= prog, tr =3D prog->aux->dst_trampoline; tgt_prog =3D prog->aux->dst_prog; } + if (prog->type =3D=3D BPF_PROG_TYPE_EXT && + prog->aux->kprobe_write_ctx !=3D tgt_prog->aux->kprobe_write_ctx) { + err =3D -EINVAL; + goto out_unlock; + } =20 err =3D bpf_link_prime(&link->link.link, &link_primer); if (err) --=20 2.53.0 From nobody Thu Apr 2 20:28:05 2026 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75AE43DD521 for ; Thu, 26 Mar 2026 14:17:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774534684; cv=none; b=qTHhl19/pRWlPL2ElBaBL2FQLFY/5qKChnzhm2y4MOKpGNMoJ7UNphZr0jYcIo4NGuqwPTLvJnszo1LlzoIbNv7XUBHDsAD6EmqcDzoJ8gObYsYK0679iqQTbkOMkxtoAnVucTQJ+YmvkdlXHCYTOlZ06U7yD3CEhS+X+FS2498= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774534684; c=relaxed/simple; bh=0Qon4HZXDLs7KJsJb3LtUW6XavGkmseM2RWCIuxU8mI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=p9kyCbw3vyr4NpCZ14OpaJ1kHeDj4l5ZVmqkSrj+1O0+u6wf7EEzLkeDcLlsUCRGWlbgUH5TXwZ3zUvxWgQeizKzCjmV9o+ShWW4cpZXXH3fdozoJ+MRhLiiW/pEXTTqgQmLRI2kHV39wzDZ1XzQuVyIPp7k9Agye+5OatNg3Mw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=xm5TdffL; arc=none smtp.client-ip=95.215.58.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="xm5TdffL" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774534676; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=h/h86vRb5ozacPc84nj3zyoBMhFdjKDRSZefVweQNT8=; b=xm5TdffLI2ncOD+YXPE61UQvdGMNyhdD5AgviaDMtEnZSZFhiN9aSlR9af6gQU5i1gwaEi MjIKAegK5OTkdbHBV0ZG3N+wxfI3sIMRgnjbYfXEhBHGhBCw3vn5cxCYuNnEZA5mZF+B4v 2f6bl4JNbv1cBLPvFEjqIaRx3/BlcXU= From: Leon Hwang To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Shuah Khan , Feng Yang , Leon Hwang , Toke Hoiland-Jorgensen , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-patches-bot@fb.com Subject: [PATCH bpf-next v2 2/2] selftests/bpf: Add test to verify the fix of kprobe_write_ctx abuse Date: Thu, 26 Mar 2026 22:17:18 +0800 Message-ID: <20260326141718.17731-3-leon.hwang@linux.dev> In-Reply-To: <20260326141718.17731-1-leon.hwang@linux.dev> References: <20260326141718.17731-1-leon.hwang@linux.dev> 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 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" Add a test to verify the issue: kprobe_write_ctx can be abused to modify struct pt_regs of kernel functions via kprobe_write_ctx=3Dtrue freplace progs. Without the fix, the issue is verified: kprobe_write_ctx=3Dtrue freplace prog is allowed to attach to kprobe_write_ctx=3Dfalse kprobe prog. Then, the first arg of bpf_fentry_test1 will be set as 0, and bpf_prog_test_run_opts() gets -EFAULT instead of 0. With the fix, the issue is rejected at attach time. Signed-off-by: Leon Hwang Acked-by: Jiri Olsa --- .../selftests/bpf/prog_tests/attach_probe.c | 64 +++++++++++++++++++ .../selftests/bpf/progs/kprobe_write_ctx.c | 19 ++++++ 2 files changed, 83 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/= testing/selftests/bpf/prog_tests/attach_probe.c index 9e77e5da7097..4d253900c4ad 100644 --- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c +++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c @@ -220,11 +220,73 @@ static void test_attach_kprobe_write_ctx(void) =20 kprobe_write_ctx__destroy(skel); } + +static void test_freplace_kprobe_write_ctx(void) +{ + struct bpf_program *prog_kprobe, *prog_ext, *prog_fentry; + struct kprobe_write_ctx *skel_kprobe, *skel_ext =3D NULL; + struct bpf_link *link_kprobe =3D NULL, *link_ext =3D NULL; + int err, prog_fd; + LIBBPF_OPTS(bpf_kprobe_opts, kprobe_opts); + LIBBPF_OPTS(bpf_test_run_opts, topts); + + skel_kprobe =3D kprobe_write_ctx__open(); + if (!ASSERT_OK_PTR(skel_kprobe, "kprobe_write_ctx__open kprobe")) + return; + + prog_kprobe =3D skel_kprobe->progs.kprobe_dummy; + bpf_program__set_autoload(prog_kprobe, true); + + prog_fentry =3D skel_kprobe->progs.fentry; + bpf_program__set_autoload(prog_fentry, true); + + err =3D kprobe_write_ctx__load(skel_kprobe); + if (!ASSERT_OK(err, "kprobe_write_ctx__load kprobe")) + goto out; + + skel_ext =3D kprobe_write_ctx__open(); + if (!ASSERT_OK_PTR(skel_ext, "kprobe_write_ctx__open ext")) + goto out; + + prog_ext =3D skel_ext->progs.freplace_kprobe; + bpf_program__set_autoload(prog_ext, true); + + prog_fd =3D bpf_program__fd(skel_kprobe->progs.kprobe_write_ctx); + bpf_program__set_attach_target(prog_ext, prog_fd, "kprobe_write_ctx"); + + err =3D kprobe_write_ctx__load(skel_ext); + if (!ASSERT_OK(err, "kprobe_write_ctx__load ext")) + goto out; + + prog_fd =3D bpf_program__fd(prog_kprobe); + link_ext =3D bpf_program__attach_freplace(prog_ext, prog_fd, "kprobe_dumm= y"); + ASSERT_ERR_PTR(link_ext, "bpf_program__attach_freplace link"); + ASSERT_EQ(errno, EINVAL, "bpf_program__attach_freplace errno"); + + link_kprobe =3D bpf_program__attach_kprobe_opts(prog_kprobe, "bpf_fentry_= test1", + &kprobe_opts); + if (!ASSERT_OK_PTR(link_kprobe, "bpf_program__attach_kprobe_opts")) + goto out; + + err =3D bpf_prog_test_run_opts(bpf_program__fd(prog_fentry), &topts); + ASSERT_OK(err, "bpf_prog_test_run_opts"); + +out: + bpf_link__destroy(link_ext); + bpf_link__destroy(link_kprobe); + kprobe_write_ctx__destroy(skel_ext); + kprobe_write_ctx__destroy(skel_kprobe); +} #else static void test_attach_kprobe_write_ctx(void) { test__skip(); } + +static void test_freplace_kprobe_write_ctx(void) +{ + test__skip(); +} #endif =20 static void test_attach_probe_auto(struct test_attach_probe *skel) @@ -434,6 +496,8 @@ void test_attach_probe(void) test_attach_kprobe_long_event_name(); if (test__start_subtest("kprobe-write-ctx")) test_attach_kprobe_write_ctx(); + if (test__start_subtest("freplace-kprobe-write-ctx")) + test_freplace_kprobe_write_ctx(); =20 cleanup: test_attach_probe__destroy(skel); diff --git a/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c b/tools/t= esting/selftests/bpf/progs/kprobe_write_ctx.c index f77aef0474d3..adbf52afe490 100644 --- a/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c +++ b/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c @@ -19,4 +19,23 @@ int kprobe_multi_write_ctx(struct pt_regs *ctx) ctx->ax =3D 0; return 0; } + +SEC("?kprobe") +int kprobe_dummy(struct pt_regs *regs) +{ + return 0; +} + +SEC("?freplace") +int freplace_kprobe(struct pt_regs *regs) +{ + regs->di =3D 0; + return 0; +} + +SEC("?fentry/bpf_fentry_test1") +int BPF_PROG(fentry) +{ + return 0; +} #endif --=20 2.53.0