[patch 07/10] selftests/rseq: Validate legacy behavior

Thomas Gleixner
2026-04-28T23:34:13Z

The RSEQ legacy mode behavior requires that the ID fields in the rseq
region are unconditionally updated on every context switch and before
signal delivery even if not required by the ABI specification.

To ensure that this behavior is preserved for legacy users in the future,
add a test which validates that with a sleep() and a signal sent to self.

Provide a run script which prevents GLIBC from registering a RSEQ region,
so that the test can register it's own legacy sized region.

Fixes: 566d8015f7ee ("rseq: Avoid CPU/MM CID updates when no event pending")
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
---
tools/testing/selftests/rseq/Makefile | 4 -
tools/testing/selftests/rseq/legacy_check.c | 65 +++++++++++++++++++++++
tools/testing/selftests/rseq/run_legacy_check.sh | 4 +
3 files changed, 71 insertions(+), 2 deletions(-)

--- a/tools/testing/selftests/rseq/Makefile
+++ b/tools/testing/selftests/rseq/Makefile
@@ -17,11 +17,11 @@ OVERRIDE_TARGETS = 1
TEST_GEN_PROGS = basic_test basic_percpu_ops_test basic_percpu_ops_mm_cid_test param_test \
param_test_benchmark param_test_compare_twice param_test_mm_cid \
param_test_mm_cid_benchmark param_test_mm_cid_compare_twice \
- syscall_errors_test slice_test
+ syscall_errors_test slice_test legacy_check

TEST_GEN_PROGS_EXTENDED = librseq.so

-TEST_PROGS = run_param_test.sh run_syscall_errors_test.sh
+TEST_PROGS = run_param_test.sh run_syscall_errors_test.sh run_legacy_check.sh

TEST_FILES := settings

--- /dev/null
+++ b/tools/testing/selftests/rseq/legacy_check.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include <errno.h>
+#include <signal.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#include "rseq.h"
+
+#include "../kselftest_harness.h"
+
+FIXTURE(legacy)
+{
+};
+
+static int cpu_id_in_sigfn = -1;
+
+static void sigfn(int sig)
+{
+ struct rseq_abi *rs = rseq_get_abi();
+
+ cpu_id_in_sigfn = rs->cpu_id_start;
+}
+
+FIXTURE_SETUP(legacy)
+{
+ int res = __rseq_register_current_thread(true, true);
+
+ switch (res) {
+ case -ENOSYS:
+ SKIP(return, "RSEQ not enabled\n");
+ case -EBUSY:
+ SKIP(return, "GLIBC owns RSEQ. Disable GLIBC RSEQ registration\n");
+ default:
+ ASSERT_EQ(res, 0);
+ }
+
+ ASSERT_NE(signal(SIGUSR1, sigfn), SIG_ERR);
+}
+
+FIXTURE_TEARDOWN(legacy)
+{
+}
+
+TEST_F(legacy, legacy_test)
+{
+ struct rseq_abi *rs = rseq_get_abi();
+
+ ASSERT_NE(rs, NULL);
+
+ /* Overwrite rs::cpu_id_start */
+ rs->cpu_id_start = -1;
+ sleep(1);
+ ASSERT_NE(rs->cpu_id_start, -1);
+
+ rs->cpu_id_start = -1;
+ ASSERT_EQ(raise(SIGUSR1), 0);
+ ASSERT_NE(rs->cpu_id_start, -1);
+ ASSERT_NE(cpu_id_in_sigfn, -1);
+}
+
+TEST_HARNESS_MAIN
--- /dev/null
+++ b/tools/testing/selftests/rseq/run_legacy_check.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+GLIBC_TUNABLES="${GLIBC_TUNABLES:-}:glibc.pthread.rseq=0" ./legacy_check