From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) (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 776953E3D95 for ; Thu, 26 Mar 2026 14:17:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774534684; cv=none; b=JM9PfQl3QkWmdtjj6ruZProwfN2EZdiyg+crNvFUkHS3rCLlgp+VauoCV7F4E5v/QahpgjOtsWs0bMN7slv2s4g0wZn64ZTWVuKZV5p34l7RAzwno3GR9rLe4ITPY/UOKQncpDrC4uZg+WWNVZgnOuN3yzfQOic8Ou4lG+H23wg= 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=95.215.58.176 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: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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=true freplace progs. Without the fix, the issue is verified: kprobe_write_ctx=true freplace prog is allowed to attach to kprobe_write_ctx=false 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 --- .../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) 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 = NULL; + struct bpf_link *link_kprobe = NULL, *link_ext = NULL; + int err, prog_fd; + LIBBPF_OPTS(bpf_kprobe_opts, kprobe_opts); + LIBBPF_OPTS(bpf_test_run_opts, topts); + + skel_kprobe = kprobe_write_ctx__open(); + if (!ASSERT_OK_PTR(skel_kprobe, "kprobe_write_ctx__open kprobe")) + return; + + prog_kprobe = skel_kprobe->progs.kprobe_dummy; + bpf_program__set_autoload(prog_kprobe, true); + + prog_fentry = skel_kprobe->progs.fentry; + bpf_program__set_autoload(prog_fentry, true); + + err = kprobe_write_ctx__load(skel_kprobe); + if (!ASSERT_OK(err, "kprobe_write_ctx__load kprobe")) + goto out; + + skel_ext = kprobe_write_ctx__open(); + if (!ASSERT_OK_PTR(skel_ext, "kprobe_write_ctx__open ext")) + goto out; + + prog_ext = skel_ext->progs.freplace_kprobe; + bpf_program__set_autoload(prog_ext, true); + + prog_fd = bpf_program__fd(skel_kprobe->progs.kprobe_write_ctx); + bpf_program__set_attach_target(prog_ext, prog_fd, "kprobe_write_ctx"); + + err = kprobe_write_ctx__load(skel_ext); + if (!ASSERT_OK(err, "kprobe_write_ctx__load ext")) + goto out; + + prog_fd = bpf_program__fd(prog_kprobe); + link_ext = bpf_program__attach_freplace(prog_ext, prog_fd, "kprobe_dummy"); + ASSERT_ERR_PTR(link_ext, "bpf_program__attach_freplace link"); + ASSERT_EQ(errno, EINVAL, "bpf_program__attach_freplace errno"); + + link_kprobe = 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 = 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 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(); cleanup: test_attach_probe__destroy(skel); diff --git a/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c b/tools/testing/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 = 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 = 0; + return 0; +} + +SEC("?fentry/bpf_fentry_test1") +int BPF_PROG(fentry) +{ + return 0; +} #endif -- 2.53.0