[PATCH 6/6] selftests/ptrace: add a test case for PTRACE_SET_SYSCALL_INFO

Dmitry V. Levin
2025-01-07T23:05:03Z

Check whether PTRACE_SET_SYSCALL_INFO semantics implemented in the
kernel matches userspace expectations.

Signed-off-by: Dmitry V. Levin <ldv@strace.io>
---
tools/testing/selftests/ptrace/Makefile | 2 +-
.../selftests/ptrace/set_syscall_info.c | 436 ++++++++++++++++++
2 files changed, 437 insertions(+), 1 deletion(-)
create mode 100644 tools/testing/selftests/ptrace/set_syscall_info.c

diff --git a/tools/testing/selftests/ptrace/Makefile b/tools/testing/selftests/ptrace/Makefile
index 1c631740a730..c5e0b76ba6ac 100644
--- a/tools/testing/selftests/ptrace/Makefile
+++ b/tools/testing/selftests/ptrace/Makefile
@@ -1,6 +1,6 @@
# SPDX-License-Identifier: GPL-2.0-only
CFLAGS += -std=c99 -pthread -Wall $(KHDR_INCLUDES)

-TEST_GEN_PROGS := get_syscall_info peeksiginfo vmaccess get_set_sud
+TEST_GEN_PROGS := get_syscall_info set_syscall_info peeksiginfo vmaccess get_set_sud

include ../lib.mk
diff --git a/tools/testing/selftests/ptrace/set_syscall_info.c b/tools/testing/selftests/ptrace/set_syscall_info.c
new file mode 100644
index 000000000000..f43294e1248e
--- /dev/null
+++ b/tools/testing/selftests/ptrace/set_syscall_info.c
@@ -0,0 +1,436 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2018-2025 Dmitry V. Levin <ldv@strace.io>
+ * All rights reserved.
+ *
+ * Check whether PTRACE_SET_SYSCALL_INFO semantics implemented in the kernel
+ * matches userspace expectations.
+ */
+
+#include "../kselftest_harness.h"
+#include <err.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <asm/unistd.h>
+#include "linux/ptrace.h"
+
+static int
+kill_tracee(pid_t pid)
+{
+ if (!pid)
+ return 0;
+
+ int saved_errno = errno;
+
+ int rc = kill(pid, SIGKILL);
+
+ errno = saved_errno;
+ return rc;
+}
+
+static long
+sys_ptrace(int request, pid_t pid, unsigned long addr, unsigned long data)
+{
+ return syscall(__NR_ptrace, request, pid, addr, data);
+}
+
+#define LOG_KILL_TRACEE(fmt, ...) \
+ do { \
+ kill_tracee(pid); \
+ TH_LOG("wait #%d: " fmt, \
+ ptrace_stop, ##__VA_ARGS__); \
+ } while (0)
+
+struct si_entry {
+ int nr;
+ unsigned long args[6];
+};
+struct si_exit {
+ unsigned int is_error;
+ int rval;
+};
+
+TEST(set_syscall_info)
+{
+ const pid_t tracer_pid = getpid();
+ const unsigned long dummy[] = {
+ 0xbad0fed0,
+ 0xbad1fed1,
+ 0xbad2fed2,
+ 0xbad3fed3,
+ 0xbad4fed4,
+ 0xbad5fed5,
+ };
+ int splice_in[2], splice_out[2];
+
+ ASSERT_EQ(0, pipe(splice_in));
+ ASSERT_EQ(0, pipe(splice_out));
+ ASSERT_EQ(sizeof(dummy), write(splice_in[1], dummy, sizeof(dummy)));
+
+ const struct {
+ struct si_entry entry[2];
+ struct si_exit exit[2];
+ } si[] = {
+ /* change scno, keep non-error rval */
+ {
+ {
+ {
+ __NR_gettid,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ __NR_getppid,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 0, tracer_pid }, { 0, tracer_pid }
+ }
+ },
+
+ /* set scno to -1, keep error rval */
+ {
+ {
+ {
+ __NR_chdir,
+ {
+ (unsigned long) ".", dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ -1,
+ {
+ (unsigned long) ".", dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 1, -ENOSYS }, { 1, -ENOSYS }
+ }
+ },
+
+ /* keep scno, change non-error rval */
+ {
+ {
+ {
+ __NR_getppid,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ __NR_getppid,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 0, tracer_pid }, { 0, tracer_pid + 1 }
+ }
+ },
+
+ /* change arg1, keep non-error rval */
+ {
+ {
+ {
+ __NR_chdir,
+ {
+ (unsigned long) "", dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ __NR_chdir,
+ {
+ (unsigned long) ".", dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 0, 0 }, { 0, 0 }
+ }
+ },
+
+ /* set scno to -1, change error rval to non-error */
+ {
+ {
+ {
+ __NR_gettid,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ -1,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 1, -ENOSYS }, { 0, tracer_pid }
+ }
+ },
+
+ /* change scno, change non-error rval to error */
+ {
+ {
+ {
+ __NR_chdir,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ __NR_getppid,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 0, tracer_pid }, { 1, -EISDIR }
+ }
+ },
+
+ /* change scno and all args, change non-error rval */
+ {
+ {
+ {
+ __NR_gettid,
+ {
+ splice_in[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ __NR_splice,
+ {
+ splice_in[0], 0, splice_out[1], 0,
+ sizeof(dummy), SPLICE_F_NONBLOCK
+ }
+ }
+ }, {
+ { 0, sizeof(dummy) }, { 0, sizeof(dummy) + 1 }
+ }
+ },
+
+ /* change arg1, no exit stop */
+ {
+ {
+ {
+ __NR_exit_group,
+ {
+ dummy[0], dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }, {
+ __NR_exit_group,
+ {
+ 0, dummy[1], dummy[2],
+ dummy[3], dummy[4], dummy[5]
+ }
+ }
+ }, {
+ { 0, 0 }, { 0, 0 }
+ }
+ },
+ };
+
+ long rc;
+ unsigned int i;
+ unsigned int ptrace_stop;
+
+ pid_t pid = fork();
+
+ ASSERT_LE(0, pid) {
+ TH_LOG("fork: %m");
+ }
+
+ if (pid == 0) {
+ /* get the pid before PTRACE_TRACEME */
+ pid = getpid();
+ ASSERT_EQ(0, sys_ptrace(PTRACE_TRACEME, 0, 0, 0)) {
+ TH_LOG("PTRACE_TRACEME: %m");
+ }
+ ASSERT_EQ(0, kill(pid, SIGSTOP)) {
+ /* cannot happen */
+ TH_LOG("kill SIGSTOP: %m");
+ }
+ for (i = 0; i < ARRAY_SIZE(si); ++i) {
+ rc = syscall(si[i].entry[0].nr,
+ si[i].entry[0].args[0],
+ si[i].entry[0].args[1],
+ si[i].entry[0].args[2],
+ si[i].entry[0].args[3],
+ si[i].entry[0].args[4],
+ si[i].entry[0].args[5]);
+ if (si[i].exit[1].is_error) {
+ if (rc != -1 || errno != -si[i].exit[1].rval)
+ break;
+ } else {
+ if (rc != si[i].exit[1].rval)
+ break;
+ }
+ }
+ /*
+ * Something went wrong, but in this state tracee
+ * cannot reliably issue syscalls, so just crash.
+ */
+ *(volatile unsigned char *) (unsigned long) i = 42;
+ /* unreachable */
+ _exit(i + 1);
+ }
+
+ for (ptrace_stop = 0; ; ++ptrace_stop) {
+ struct ptrace_syscall_info info = {
+ .op = 0xff /* invalid PTRACE_SYSCALL_INFO_* op */
+ };
+ const size_t size = sizeof(info);
+ const int expected_entry_size =
+ (void *) &info.entry.args[6] - (void *) &info;
+ const int expected_exit_size =
+ (void *) (&info.exit.is_error + 1) -
+ (void *) &info;
+ int status;
+
+ ASSERT_EQ(pid, wait(&status)) {
+ /* cannot happen */
+ LOG_KILL_TRACEE("wait: %m");
+ }
+ if (WIFEXITED(status)) {
+ pid = 0; /* the tracee is no more */
+ ASSERT_EQ(0, WEXITSTATUS(status)) {
+ LOG_KILL_TRACEE("unexpected exit status %u",
+ WEXITSTATUS(status));
+ }
+ break;
+ }
+ ASSERT_FALSE(WIFSIGNALED(status)) {
+ pid = 0; /* the tracee is no more */
+ LOG_KILL_TRACEE("unexpected signal %u",
+ WTERMSIG(status));
+ }
+ ASSERT_TRUE(WIFSTOPPED(status)) {
+ /* cannot happen */
+ LOG_KILL_TRACEE("unexpected wait status %#x", status);
+ }
+
+ ASSERT_LT(ptrace_stop, ARRAY_SIZE(si) * 2) {
+ LOG_KILL_TRACEE("ptrace stop overflow");
+ }
+
+ switch (WSTOPSIG(status)) {
+ case SIGSTOP:
+ ASSERT_EQ(0, ptrace_stop) {
+ LOG_KILL_TRACEE("unexpected signal stop");
+ }
+ ASSERT_EQ(0, sys_ptrace(PTRACE_SETOPTIONS, pid, 0,
+ PTRACE_O_TRACESYSGOOD)) {
+ LOG_KILL_TRACEE("PTRACE_SETOPTIONS: %m");
+ }
+ break;
+
+ case SIGTRAP | 0x80:
+ ASSERT_LT(0, ptrace_stop) {
+ LOG_KILL_TRACEE("unexpected syscall stop");
+ }
+ ASSERT_LT(0, (rc = sys_ptrace(PTRACE_GET_SYSCALL_INFO,
+ pid, size,
+ (unsigned long) &info))) {
+ LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO: %m");
+ }
+ if (ptrace_stop & 1) {
+ /* entering syscall */
+ const struct si_entry *exp_entry =
+ &si[ptrace_stop / 2].entry[0];
+ const struct si_entry *set_entry =
+ &si[ptrace_stop / 2].entry[1];
+
+ ASSERT_EQ(expected_entry_size, rc) {
+ LOG_KILL_TRACEE("entry stop mismatch");
+ }
+ ASSERT_EQ(PTRACE_SYSCALL_INFO_ENTRY, info.op) {
+ LOG_KILL_TRACEE("entry stop mismatch");
+ }
+ ASSERT_TRUE(info.arch) {
+ LOG_KILL_TRACEE("entry stop mismatch");
+ }
+ ASSERT_TRUE(info.instruction_pointer) {
+ LOG_KILL_TRACEE("entry stop mismatch");
+ }
+ ASSERT_TRUE(info.stack_pointer) {
+ LOG_KILL_TRACEE("entry stop mismatch");
+ }
+ ASSERT_EQ(exp_entry->nr, info.entry.nr) {
+ LOG_KILL_TRACEE("syscall nr mismatch");
+ }
+ for (i = 0; i < ARRAY_SIZE(exp_entry->args); ++i) {
+ ASSERT_EQ(exp_entry->args[i], info.entry.args[i]) {
+ LOG_KILL_TRACEE("syscall arg #%u mismatch", i);
+ }
+ }
+ info.entry.nr = set_entry->nr;
+ for (i = 0; i < ARRAY_SIZE(set_entry->args); ++i)
+ info.entry.args[i] = set_entry->args[i];
+ ASSERT_EQ(0, sys_ptrace(PTRACE_SET_SYSCALL_INFO,
+ pid, size,
+ (unsigned long) &info)) {
+ LOG_KILL_TRACEE("PTRACE_SET_SYSCALL_INFO: %m");
+ }
+ } else {
+ /* exiting syscall */
+ const struct si_exit *exp_exit =
+ &si[ptrace_stop / 2 - 1].exit[0];
+ const struct si_exit *set_exit =
+ &si[ptrace_stop / 2 - 1].exit[1];
+
+ ASSERT_EQ(expected_exit_size, rc) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ ASSERT_EQ(PTRACE_SYSCALL_INFO_EXIT, info.op) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ ASSERT_TRUE(info.arch) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ ASSERT_TRUE(info.instruction_pointer) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ ASSERT_TRUE(info.stack_pointer) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ ASSERT_EQ(exp_exit->is_error, info.exit.is_error) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ ASSERT_EQ(exp_exit->rval, info.exit.rval) {
+ LOG_KILL_TRACEE("exit stop mismatch");
+ }
+ info.exit.is_error = set_exit->is_error;
+ info.exit.rval = set_exit->rval;
+ ASSERT_EQ(0, sys_ptrace(PTRACE_SET_SYSCALL_INFO,
+ pid, size,
+ (unsigned long) &info)) {
+ LOG_KILL_TRACEE("PTRACE_SET_SYSCALL_INFO: %m");
+ }
+ }
+ break;
+
+ default:
+ LOG_KILL_TRACEE("unexpected stop signal %u",
+ WSTOPSIG(status));
+ abort();
+ }
+
+ ASSERT_EQ(0, sys_ptrace(PTRACE_SYSCALL, pid, 0, 0)) {
+ LOG_KILL_TRACEE("PTRACE_SYSCALL: %m");
+ }
+ }
+
+ ASSERT_EQ(ptrace_stop, ARRAY_SIZE(si) * 2);
+}
+
+TEST_HARNESS_MAIN

--
ldv