tools/testing/selftests/ptrace/set_syscall_info.c

// 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/types.h>
#include <linux/ptrace.h>

#if defined(_MIPS_SIM) && _MIPS_SIM == _MIPS_SIM_NABI32
/*
 * MIPS N32 is the only architecture where __kernel_ulong_t
 * does not match the bitness of syscall arguments.
 */
typedef unsigned long long kernel_ulong_t;
#else
typedef __kernel_ulong_t kernel_ulong_t;
#endif

struct si_entry {
	int nr;
	kernel_ulong_t args[6];
};
struct si_exit {
	unsigned int is_error;
	int rval;
};

static unsigned int ptrace_stop;
static pid_t tracee_pid;

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(tracee_pid);			\
		TH_LOG("wait #%d: " fmt,			\
		       ptrace_stop, ##__VA_ARGS__);		\
	} while (0)

static void
check_psi_entry(struct __test_metadata *_metadata,
		const struct ptrace_syscall_info *info,
		const struct si_entry *exp_entry,
		const char *text)
{
	unsigned int i;
	int exp_nr = exp_entry->nr;
#if defined __s390__ || defined __s390x__
	/* s390 is the only architecture that has 16-bit syscall numbers */
	exp_nr &= 0xffff;
#endif

	ASSERT_EQ(PTRACE_SYSCALL_INFO_ENTRY, info->op) {
		LOG_KILL_TRACEE("%s: entry stop mismatch", text);
	}
	ASSERT_TRUE(info->arch) {
		LOG_KILL_TRACEE("%s: entry stop mismatch", text);
	}
	ASSERT_TRUE(info->instruction_pointer) {
		LOG_KILL_TRACEE("%s: entry stop mismatch", text);
	}
	ASSERT_TRUE(info->stack_pointer) {
		LOG_KILL_TRACEE("%s: entry stop mismatch", text);
	}
	ASSERT_EQ(exp_nr, info->entry.nr) {
		LOG_KILL_TRACEE("%s: syscall nr mismatch", text);
	}
	for (i = 0; i < ARRAY_SIZE(exp_entry->args); ++i) {
		ASSERT_EQ(exp_entry->args[i], info->entry.args[i]) {
			LOG_KILL_TRACEE("%s: syscall arg #%u mismatch",
					text, i);
		}
	}
}

static void
check_psi_exit(struct __test_metadata *_metadata,
	       const struct ptrace_syscall_info *info,
	       const struct si_exit *exp_exit,
	       const char *text)
{
	ASSERT_EQ(PTRACE_SYSCALL_INFO_EXIT, info->op) {
		LOG_KILL_TRACEE("%s: exit stop mismatch", text);
	}
	ASSERT_TRUE(info->arch) {
		LOG_KILL_TRACEE("%s: exit stop mismatch", text);
	}
	ASSERT_TRUE(info->instruction_pointer) {
		LOG_KILL_TRACEE("%s: exit stop mismatch", text);
	}
	ASSERT_TRUE(info->stack_pointer) {
		LOG_KILL_TRACEE("%s: exit stop mismatch", text);
	}
	ASSERT_EQ(exp_exit->is_error, info->exit.is_error) {
		LOG_KILL_TRACEE("%s: exit stop mismatch", text);
	}
	ASSERT_EQ(exp_exit->rval, info->exit.rval) {
		LOG_KILL_TRACEE("%s: exit stop mismatch", text);
	}
}

TEST(set_syscall_info)
{
	const pid_t tracer_pid = getpid();
	const kernel_ulong_t dummy[] = {
		(kernel_ulong_t) 0xdad0bef0bad0fed0ULL,
		(kernel_ulong_t) 0xdad1bef1bad1fed1ULL,
		(kernel_ulong_t) 0xdad2bef2bad2fed2ULL,
		(kernel_ulong_t) 0xdad3bef3bad3fed3ULL,
		(kernel_ulong_t) 0xdad4bef4bad4fed4ULL,
		(kernel_ulong_t) 0xdad5bef5bad5fed5ULL,
	};
	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,
					{
						(uintptr_t) ".",
						dummy[1], dummy[2],
						dummy[3], dummy[4], dummy[5]
					}
				}, {
					-1,
					{
						(uintptr_t) ".",
						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,
					{
						(uintptr_t) "",
						dummy[1], dummy[2],
						dummy[3], dummy[4], dummy[5]
					}
				}, {
					__NR_chdir,
					{
						(uintptr_t) ".",
						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,
					{
						dummy[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;

	tracee_pid = fork();

	ASSERT_LE(0, tracee_pid) {
		TH_LOG("fork: %m");
	}

	if (tracee_pid == 0) {
		/* get the pid before PTRACE_TRACEME */
		tracee_pid = getpid();
		ASSERT_EQ(0, sys_ptrace(PTRACE_TRACEME, 0, 0, 0)) {
			TH_LOG("PTRACE_TRACEME: %m");
		}
		ASSERT_EQ(0, kill(tracee_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 *) (uintptr_t) 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(tracee_pid, wait(&status)) {
			/* cannot happen */
			LOG_KILL_TRACEE("wait: %m");
		}
		if (WIFEXITED(status)) {
			tracee_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)) {
			tracee_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, tracee_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,
						      tracee_pid, size,
						      (uintptr_t) &info))) {
				LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO #1: %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];

				/* check ptrace_syscall_info before the changes */
				ASSERT_EQ(expected_entry_size, rc) {
					LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO #1"
							": entry stop mismatch");
				}
				check_psi_entry(_metadata, &info, exp_entry,
						"PTRACE_GET_SYSCALL_INFO #1");

				/* apply the changes */
				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,
							tracee_pid, size,
							(uintptr_t) &info)) {
					LOG_KILL_TRACEE("PTRACE_SET_SYSCALL_INFO: %m");
				}

				/* check ptrace_syscall_info after the changes */
				memset(&info, 0, sizeof(info));
				info.op = 0xff;
				ASSERT_LT(0, (rc = sys_ptrace(PTRACE_GET_SYSCALL_INFO,
							      tracee_pid, size,
							      (uintptr_t) &info))) {
					LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO: %m");
				}
				ASSERT_EQ(expected_entry_size, rc) {
					LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO #2"
							": entry stop mismatch");
				}
				check_psi_entry(_metadata, &info, set_entry,
						"PTRACE_GET_SYSCALL_INFO #2");
			} 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];

				/* check ptrace_syscall_info before the changes */
				ASSERT_EQ(expected_exit_size, rc) {
					LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO #1"
							": exit stop mismatch");
				}
				check_psi_exit(_metadata, &info, exp_exit,
						"PTRACE_GET_SYSCALL_INFO #1");

				/* apply the changes */
				info.exit.is_error = set_exit->is_error;
				info.exit.rval = set_exit->rval;
				ASSERT_EQ(0, sys_ptrace(PTRACE_SET_SYSCALL_INFO,
							tracee_pid, size,
							(uintptr_t) &info)) {
					LOG_KILL_TRACEE("PTRACE_SET_SYSCALL_INFO: %m");
				}

				/* check ptrace_syscall_info after the changes */
				memset(&info, 0, sizeof(info));
				info.op = 0xff;
				ASSERT_LT(0, (rc = sys_ptrace(PTRACE_GET_SYSCALL_INFO,
							      tracee_pid, size,
							      (uintptr_t) &info))) {
					LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO #2: %m");
				}
				ASSERT_EQ(expected_exit_size, rc) {
					LOG_KILL_TRACEE("PTRACE_GET_SYSCALL_INFO #2"
							": exit stop mismatch");
				}
				check_psi_exit(_metadata, &info, set_exit,
						"PTRACE_GET_SYSCALL_INFO #2");
			}
			break;

		default:
			LOG_KILL_TRACEE("unexpected stop signal %u",
					WSTOPSIG(status));
			abort();
		}

		ASSERT_EQ(0, sys_ptrace(PTRACE_SYSCALL, tracee_pid, 0, 0)) {
			LOG_KILL_TRACEE("PTRACE_SYSCALL: %m");
		}
	}

	ASSERT_EQ(ptrace_stop, ARRAY_SIZE(si) * 2);
}

TEST_HARNESS_MAIN