This test adds coverage of expected errors during rseq registration and
unregistration, it disables glibc integration and will thus always
exercise the rseq syscall explictly.

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
---
 tools/testing/selftests/rseq/.gitignore       |   1 +
 tools/testing/selftests/rseq/Makefile         |   9 +-
 tools/testing/selftests/rseq/rseq.c           |   6 +-
 tools/testing/selftests/rseq/rseq.h           |   5 +
 .../selftests/rseq/run_syscall_errors_test.sh |   5 +
 .../selftests/rseq/syscall_errors_test.c      | 124 ++++++++++++++++++
 6 files changed, 145 insertions(+), 5 deletions(-)
 create mode 100755 tools/testing/selftests/rseq/run_syscall_errors_test.sh
 create mode 100644 tools/testing/selftests/rseq/syscall_errors_test.c

diff --git a/tools/testing/selftests/rseq/.gitignore b/tools/testing/selftests/rseq/.gitignore
index 16496de5f6ce..0fda241fa62b 100644
--- a/tools/testing/selftests/rseq/.gitignore
+++ b/tools/testing/selftests/rseq/.gitignore
@@ -9,3 +9,4 @@ param_test_compare_twice
 param_test_mm_cid
 param_test_mm_cid_benchmark
 param_test_mm_cid_compare_twice
+syscall_errors_test
diff --git a/tools/testing/selftests/rseq/Makefile b/tools/testing/selftests/rseq/Makefile
index 5a3432fceb58..0d0a5fae5954 100644
--- a/tools/testing/selftests/rseq/Makefile
+++ b/tools/testing/selftests/rseq/Makefile
@@ -16,11 +16,12 @@ 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
+		param_test_mm_cid_benchmark param_test_mm_cid_compare_twice \
+		syscall_errors_test
 
 TEST_GEN_PROGS_EXTENDED = librseq.so
 
-TEST_PROGS = run_param_test.sh
+TEST_PROGS = run_param_test.sh run_syscall_errors_test.sh
 
 TEST_FILES := settings
 
@@ -54,3 +55,7 @@ $(OUTPUT)/param_test_mm_cid_benchmark: param_test.c $(TEST_GEN_PROGS_EXTENDED) \
 $(OUTPUT)/param_test_mm_cid_compare_twice: param_test.c $(TEST_GEN_PROGS_EXTENDED) \
 					rseq.h rseq-*.h
 	$(CC) $(CFLAGS) -DBUILDOPT_RSEQ_PERCPU_MM_CID -DRSEQ_COMPARE_TWICE $< $(LDLIBS) -lrseq -o $@
+
+$(OUTPUT)/syscall_errors_test: syscall_errors_test.c $(TEST_GEN_PROGS_EXTENDED) \
+					rseq.h rseq-*.h
+	$(CC) $(CFLAGS) $< $(LDLIBS) -lrseq -o $@
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 5b9772cdf265..4c06b8f61fe5 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -88,7 +88,7 @@ static int sys_getcpu(unsigned *cpu, unsigned *node)
 	return syscall(__NR_getcpu, cpu, node, NULL);
 }
 
-int rseq_available(void)
+bool rseq_available(void)
 {
 	int rc;
 
@@ -97,9 +97,9 @@ int rseq_available(void)
 		abort();
 	switch (errno) {
 	case ENOSYS:
-		return 0;
+		return false;
 	case EINVAL:
-		return 1;
+		return true;
 	default:
 		abort();
 	}
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index 4e217b620e0c..7c3c018d2ba0 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -150,6 +150,11 @@ int32_t rseq_fallback_current_cpu(void);
  */
 int32_t rseq_fallback_current_node(void);
 
+/*
+ * Returns true if rseq is supported.
+ */
+bool rseq_available(void);
+
 /*
  * Values returned can be either the current CPU number, -1 (rseq is
  * uninitialized), or -2 (rseq initialization has failed).
diff --git a/tools/testing/selftests/rseq/run_syscall_errors_test.sh b/tools/testing/selftests/rseq/run_syscall_errors_test.sh
new file mode 100755
index 000000000000..9272246b39f2
--- /dev/null
+++ b/tools/testing/selftests/rseq/run_syscall_errors_test.sh
@@ -0,0 +1,5 @@
+#!/bin/bash
+# SPDX-License-Identifier: MIT
+# SPDX-FileCopyrightText: 2024 Michael Jeanson <mjeanson@efficios.com>
+
+GLIBC_TUNABLES="${GLIBC_TUNABLES:-}:glibc.pthread.rseq=0" ./syscall_errors_test
diff --git a/tools/testing/selftests/rseq/syscall_errors_test.c b/tools/testing/selftests/rseq/syscall_errors_test.c
new file mode 100644
index 000000000000..a5d9e1f8a2dc
--- /dev/null
+++ b/tools/testing/selftests/rseq/syscall_errors_test.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2024 Michael Jeanson <mjeanson@efficios.com>
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include <assert.h>
+#include <stdint.h>
+#include <syscall.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "rseq.h"
+
+static int sys_rseq(void *rseq_abi, uint32_t rseq_len,
+		    int flags, uint32_t sig)
+{
+	return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
+}
+
+/*
+ * Check the value of errno on some expected failures of the rseq syscall.
+ */
+
+int main(void)
+{
+	struct rseq_abi *global_rseq = rseq_get_abi();
+	int ret;
+	int errno_copy;
+
+	if (!rseq_available()) {
+		fprintf(stderr, "rseq syscall unavailable");
+		goto error;
+	}
+
+	/* The current thread is NOT registered. */
+
+	/* EINVAL */
+	errno = 0;
+	ret = sys_rseq(global_rseq, 32, -1, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Registration with invalid flag fails with errno set to EINVAL (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EINVAL)
+		goto error;
+
+	errno = 0;
+	ret = sys_rseq((char *) global_rseq + 1, 32, 0, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Registration with unaligned rseq_abi fails with errno set to EINVAL (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EINVAL)
+		goto error;
+
+	errno = 0;
+	ret = sys_rseq(global_rseq, 31, 0, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Registration with invalid size fails with errno set to EINVAL (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EINVAL)
+		goto error;
+
+
+#if defined(__LP64__) && (!defined(__s390__) && !defined(__s390x__))
+	/*
+	 * We haven't found a reliable way to find an invalid address when
+	 * running a 32bit userspace on a 64bit kernel, so only run this test
+	 * on 64bit builds for the moment.
+	 *
+	 * Also exclude architectures that select
+	 * CONFIG_ALTERNATE_USER_ADDRESS_SPACE where the kernel and userspace
+	 * have their own address space and this failure can't happen.
+	 */
+
+	/* EFAULT */
+	errno = 0;
+	ret = sys_rseq((void *) -4096UL, 32, 0, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Registration with invalid address fails with errno set to EFAULT (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EFAULT)
+		goto error;
+#endif
+
+	errno = 0;
+	ret = sys_rseq(global_rseq, 32, 0, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Registration succeeds for the current thread (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret != 0 && errno != 0)
+		goto error;
+
+	/* The current thread is registered. */
+
+	/* EBUSY */
+	errno = 0;
+	ret = sys_rseq(global_rseq, 32, 0, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Double registration fails with errno set to EBUSY (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EBUSY)
+		goto error;
+
+	/* EPERM */
+	errno = 0;
+	ret = sys_rseq(global_rseq, 32, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG + 1);
+	errno_copy = errno;
+	fprintf(stderr, "Unregistration with wrong RSEQ_SIG fails with errno to EPERM (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EPERM)
+		goto error;
+
+	errno = 0;
+	ret = sys_rseq(global_rseq, 32, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Unregistration succeeds for the current thread (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret != 0)
+		goto error;
+
+	errno = 0;
+	ret = sys_rseq(global_rseq, 32, RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
+	errno_copy = errno;
+	fprintf(stderr, "Double unregistration fails with errno set to EINVAL (ret = %d, errno = %s)\n", ret, strerrorname_np(errno_copy));
+	if (ret == 0 || errno_copy != EINVAL)
+		goto error;
+
+	return 0;
+error:
+	return -1;
+}
-- 
2.43.0