linux-kernel - [PATCHv4 bpf-next 5/6] selftests/bpf: Add kprobe write ctx attach test

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Message-ID: <20250916215301.664963-6-jolsa@kernel.org>
Date: Tue, 16 Sep 2025 23:53:00 +0200
From: Jiri Olsa <jolsa@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	x86@...nel.org,
	Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCHv4 bpf-next 5/6] selftests/bpf: Add kprobe write ctx attach test

Adding test to check we can't attach standard kprobe program that
writes to the context.

It's x86_64 specific test.

Acked-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 .../selftests/bpf/prog_tests/attach_probe.c   | 28 +++++++++++++++++++
 .../selftests/bpf/progs/kprobe_write_ctx.c    | 15 ++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/kprobe_write_ctx.c

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index cabc51c2ca6b..9e77e5da7097 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -3,6 +3,7 @@
 #include "test_attach_kprobe_sleepable.skel.h"
 #include "test_attach_probe_manual.skel.h"
 #include "test_attach_probe.skel.h"
+#include "kprobe_write_ctx.skel.h"
 
 /* this is how USDT semaphore is actually defined, except volatile modifier */
 volatile unsigned short uprobe_ref_ctr __attribute__((unused)) __attribute((section(".probes")));
@@ -201,6 +202,31 @@ static void test_attach_kprobe_long_event_name(void)
 	test_attach_probe_manual__destroy(skel);
 }
 
+#ifdef __x86_64__
+/* attach kprobe/kretprobe long event name testings */
+static void test_attach_kprobe_write_ctx(void)
+{
+	struct kprobe_write_ctx *skel = NULL;
+	struct bpf_link *link = NULL;
+
+	skel = kprobe_write_ctx__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "kprobe_write_ctx__open_and_load"))
+		return;
+
+	link = bpf_program__attach_kprobe_opts(skel->progs.kprobe_write_ctx,
+					     "bpf_fentry_test1", NULL);
+	if (!ASSERT_ERR_PTR(link, "bpf_program__attach_kprobe_opts"))
+		bpf_link__destroy(link);
+
+	kprobe_write_ctx__destroy(skel);
+}
+#else
+static void test_attach_kprobe_write_ctx(void)
+{
+	test__skip();
+}
+#endif
+
 static void test_attach_probe_auto(struct test_attach_probe *skel)
 {
 	struct bpf_link *uprobe_err_link;
@@ -406,6 +432,8 @@ void test_attach_probe(void)
 		test_attach_uprobe_long_event_name();
 	if (test__start_subtest("kprobe-long_name"))
 		test_attach_kprobe_long_event_name();
+	if (test__start_subtest("kprobe-write-ctx"))
+		test_attach_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
new file mode 100644
index 000000000000..4621a5bef4e2
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kprobe_write_ctx.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+#if defined(__TARGET_ARCH_x86)
+SEC("kprobe")
+int kprobe_write_ctx(struct pt_regs *ctx)
+{
+	ctx->ax = 0;
+	return 0;
+}
+#endif
-- 
2.51.0