[v3,3/3] x86: Add test for arch_prctl(ARCH_VSYSCALL_CONTROL)

Commit Message

Florian Weimer Jan. 5, 2022, 4:03 p.m. UTC

Signed-off-by: Florian Weimer <[e-mail]>
---
v3: Patch split out.

 tools/arch/x86/include/uapi/asm/prctl.h       |   2 +
 tools/testing/selftests/x86/Makefile          |   7 +-
 .../testing/selftests/x86/vsyscall_control.c  | 891 ++++++++++++++++++
 3 files changed, 899 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/x86/vsyscall_control.c

Comments

Andy Lutomirski Jan. 13, 2022, 9:31 p.m. UTC | #1

On 1/5/22 08:03, Florian Weimer wrote:
> Signed-off-by: Florian Weimer <[e-mail]>

This seems like a respectable test case, but why does it work so hard to 
avoid using libc?  Is there something I shuold know about glibc that 
makes its maintainer not want to use it :-p

--Andy

> ---
> v3: Patch split out.
> 
>   tools/arch/x86/include/uapi/asm/prctl.h       |   2 +
>   tools/testing/selftests/x86/Makefile          |   7 +-
>   .../testing/selftests/x86/vsyscall_control.c  | 891 ++++++++++++++++++
>   3 files changed, 899 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/x86/vsyscall_control.c
> 
> diff --git a/tools/arch/x86/include/uapi/asm/prctl.h b/tools/arch/x86/include/uapi/asm/prctl.h
> index 754a07856817..aad0bcfbf49f 100644
> --- a/tools/arch/x86/include/uapi/asm/prctl.h
> +++ b/tools/arch/x86/include/uapi/asm/prctl.h
> @@ -18,4 +18,6 @@
>   #define ARCH_MAP_VDSO_32	0x2002
>   #define ARCH_MAP_VDSO_64	0x2003
>   
> +#define ARCH_VSYSCALL_CONTROL	0x5001
> +
>   #endif /* _ASM_X86_PRCTL_H */
> diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
> index 0993d12f2c38..4c751836bfeb 100644
> --- a/tools/testing/selftests/x86/Makefile
> +++ b/tools/testing/selftests/x86/Makefile
> @@ -18,7 +18,7 @@ TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \
>   			test_FCMOV test_FCOMI test_FISTTP \
>   			vdso_restorer
>   TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
> -			corrupt_xstate_header amx
> +			corrupt_xstate_header amx vsyscall_control
>   # Some selftests require 32bit support enabled also on 64bit systems
>   TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
>   
> @@ -107,3 +107,8 @@ $(OUTPUT)/test_syscall_vdso_32: thunks_32.S
>   # state.
>   $(OUTPUT)/check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
>   $(OUTPUT)/check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
> +
> +# This test does not link against anything (neither libc nor libgcc).
> +$(OUTPUT)/vsyscall_control_64: \
> +	LIBS := -Wl,-no-pie -static -nostdlib -nostartfiles
> +	CFLAGS += -fno-pie -fno-stack-protector -fno-builtin -ffreestanding
> diff --git a/tools/testing/selftests/x86/vsyscall_control.c b/tools/testing/selftests/x86/vsyscall_control.c
> new file mode 100644
> index 000000000000..ee966f936c89
> --- /dev/null
> +++ b/tools/testing/selftests/x86/vsyscall_control.c
> @@ -0,0 +1,891 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * vsyscall_lockout.c - check that disabling vsyscall works
> + * Copyright (C) 2021 Red Hat, Inc.
> + *
> + * This test requires vsyscall=xonly or vsyscall=emulate.  With
> + * vsyscall=emulate, ARCH_VSYSCALL_CONTROL cannot turn off vsyscall
> + * completely (reads still work), but this is not tested here.
> + */
> +
> +#include <stddef.h>
> +
> +#include <asm/prctl.h>
> +#include <asm/vsyscall.h>
> +#include <linux/errno.h>
> +#include <linux/fcntl.h>
> +#include <linux/signal.h>
> +#include <linux/time.h>
> +#include <linux/types.h>
> +#include <linux/unistd.h>
> +
> +#ifndef ARCH_VSYSCALL_CONTROL
> +#define ARCH_VSYSCALL_CONTROL	0x5001
> +#elif ARCH_VSYSCALL_CONTROL != 0x5001
> +#error wrong vlaue for ARCH_VSYSCALL_CONTROL
> +#endif
> +
> +
> +static inline long syscall0(int nr)
> +{
> +	unsigned long result;
> +
> +	__asm__ volatile ("syscall"
> +			  : "=a" (result)
> +			  : "0" (nr)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static inline long syscall1(int nr, long arg0)
> +{
> +	register long rdi asm("rdi") = arg0;
> +	unsigned long result;
> +
> +	__asm__ volatile ("syscall"
> +			  : "=a" (result)
> +			  : "0" (nr), "r" (rdi)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static inline long syscall2(int nr, long arg0, long arg1)
> +{
> +	register long rdi asm("rdi") = arg0;
> +	register long rsi asm("rsi") = arg1;
> +	unsigned long result;
> +
> +	__asm__ volatile ("syscall"
> +			  : "=a" (result)
> +			  : "0" (nr), "r" (rdi), "r" (rsi)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static inline long syscall3(int nr, long arg0, long arg1, long arg2)
> +{
> +	register long rdi asm("rdi") = arg0;
> +	register long rsi asm("rsi") = arg1;
> +	register long rdx asm("rdx") = arg2;
> +	unsigned long result;
> +
> +	__asm__ volatile ("syscall"
> +			  : "=a" (result)
> +			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static inline long syscall4(int nr, long arg0, long arg1, long arg2, long arg3)
> +{
> +	register long rdi asm("rdi") = arg0;
> +	register long rsi asm("rsi") = arg1;
> +	register long rdx asm("rdx") = arg2;
> +	register long r10 asm("r10") = arg3;
> +	unsigned long result;
> +
> +	__asm__ volatile ("syscall"
> +			  : "=a" (result)
> +			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx),
> +			    "r" (r10)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static inline long syscall5(int nr, long arg0, long arg1, long arg2, long arg3,
> +			    long arg4)
> +{
> +	register long rdi asm("rdi") = arg0;
> +	register long rsi asm("rsi") = arg1;
> +	register long rdx asm("rdx") = arg2;
> +	register long r10 asm("r10") = arg3;
> +	register long r8 asm("r8") = arg4;
> +	unsigned long result;
> +
> +	__asm__ volatile ("syscall"
> +			  : "=a" (result)
> +			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx),
> +			    "r" (r10), "r" (r8)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static inline long vsyscall2(long addr, long arg0, long arg1)
> +{
> +	register long rdi asm("rdi") = arg0;
> +	register long rsi asm("rsi") = arg1;
> +	unsigned long result;
> +
> +	__asm__ volatile ("callq *%%rax"
> +			  : "=a" (result)
> +			  : "0" (addr), "r" (rdi), "r" (rsi)
> +			  : "memory", "cc", "r11", "cx");
> +	return result;
> +}
> +
> +static void __attribute__ ((noreturn)) sys_exit(int status)
> +{
> +	syscall1(__NR_exit, status);
> +	__builtin_unreachable();
> +}
> +
> +static int sys_access(const char *pathname, int mode)
> +{
> +	return syscall2(__NR_access, (long) pathname, mode);
> +}
> +
> +static int sys_mkdir(const char *pathname, __kernel_mode_t mode)
> +{
> +	return syscall2(__NR_mkdir, (long) pathname, mode);
> +}
> +
> +static int sys_open(const char *pathname, int flags, __kernel_mode_t mode)
> +{
> +	return syscall3(__NR_open, (long) pathname, flags, mode);
> +}
> +
> +static long sys_read(int fd, void *buffer, size_t length)
> +{
> +	return syscall3(__NR_read, fd, (long) buffer, length);
> +}
> +
> +static long sys_write(int fd, const void *buffer, size_t length)
> +{
> +	return syscall3(__NR_write, fd, (long) buffer, length);
> +}
> +
> +static int sys_mount(const char *source, const char *pathname,
> +		     const char *fstype, unsigned long flags,
> +		     const void *data)
> +{
> +	return syscall5(__NR_mount, (long) source, (long) pathname,
> +			(long) fstype, flags, (long) data);
> +}
> +
> +static void sigabrt(void)
> +{
> +	syscall2(__NR_kill, syscall0(__NR_getpid), SIGABRT);
> +}
> +
> +/*
> + * String buffers.
> + */
> +
> +struct buffer {
> +	char *position;
> +	char *limit;
> +};
> +
> +static void buffer_init(struct buffer *b, char *start, size_t length)
> +{
> +	b->position = start;
> +	b->limit = start + length;
> +}
> +
> +static void buffer_append(struct buffer *b, char ch)
> +{
> +	if (b->position >= b->limit)
> +		sigabrt();
> +	*b->position = ch;
> +	++b->position;
> +}
> +
> +static void buffer_append_string(struct buffer *b, const char *p)
> +{
> +	while (*p) {
> +		buffer_append(b, *p);
> +		++p;
> +	}
> +}
> +
> +static void buffer_append_dec_1(struct buffer *b, unsigned long val)
> +{
> +	if (val != 0) {
> +		buffer_append_dec_1(b, val / 10);
> +		buffer_append(b, '0' + (val % 10));
> +	}
> +}
> +
> +static void buffer_append_dec(struct buffer *b, unsigned long val)
> +{
> +	if (val == 0) {
> +		buffer_append(b, '0');
> +		return;
> +	}
> +	buffer_append_dec_1(b, val);
> +}
> +
> +/*
> + * Output to standard output.
> + */
> +
> +static void print_char(char byte)
> +{
> +	if (sys_write(1, &byte, 1) < 0)
> +		sigabrt();
> +}
> +
> +static void print_string(const char *p)
> +{
> +	while (*p) {
> +		print_char(*p);
> +		++p;
> +	}
> +}
> +
> +static void print_dec_1(unsigned long val)
> +{
> +	if (val != 0) {
> +		print_dec_1(val / 10);
> +		print_char('0' + (val % 10));
> +	}
> +}
> +
> +static void print_dec(unsigned long val)
> +{
> +	if (val == 0)
> +		print_char('0');
> +	else
> +		print_dec_1(val);
> +}
> +
> +static void print_signed_dec(long val)
> +{
> +	if (val < 0) {
> +		print_char('-');
> +		print_dec(-(unsigned long)val);
> +	} else
> +		print_dec(val);
> +}
> +
> +static void print_message(unsigned int lineno, const char *tag, const char *p)
> +{
> +	print_string(__FILE__);
> +	print_char(':');
> +	print_dec(lineno);
> +	print_char(':');
> +	print_char(' ');
> +	print_string(tag);
> +	print_char(':');
> +	print_char(' ');
> +	print_string(p);
> +}
> +
> +static void print_info(unsigned int lineno, const char *p)
> +{
> +	print_message(lineno, "info", p);
> +}
> +
> +static void print_error(unsigned int lineno, const char *p)
> +{
> +	print_message(lineno, "ERROR", p);
> +}
> +
> +static void print_failure(int lineno, const char *label, long ret)
> +{
> +	print_error(lineno, label);
> +	print_string(" failed: ");
> +	print_signed_dec(ret);
> +	print_char('\n');
> +}
> +
> +static void print_time(int lineno, const char *label, struct timeval tv)
> +{
> +	print_info(lineno, label);
> +	print_string(": ");
> +	print_dec(tv.tv_sec);
> +	print_char(' ');
> +	print_dec(tv.tv_usec);
> +	print_char('\n');
> +}
> +
> +/*
> + * Process-failing (v)syscall wrappers.
> + */
> +
> +static void xgettimeofday(struct timeval *tv)
> +{
> +	long ret = syscall2(__NR_gettimeofday, (long) tv, 0);
> +
> +	if (ret != 0) {
> +		print_failure(__LINE__, "gettimeofday", ret);
> +		sigabrt();
> +	}
> +}
> +
> +static void xvgettimeofday(struct timeval *tv)
> +{
> +	long ret = vsyscall2(VSYSCALL_ADDR, (long) tv, 0);
> +
> +	if (ret) {
> +		print_failure(__LINE__, "vgettimeofday", ret);
> +		sigabrt();
> +	}
> +}
> +
> +static int sys_arch_prctl(int code, unsigned long addr)
> +{
> +	return syscall2(__NR_arch_prctl, code, addr);
> +}
> +
> +static void xclose(int fd)
> +{
> +	long ret = syscall1(__NR_close, fd);
> +
> +	if (ret < 0) {
> +		print_failure(__LINE__, "close", ret);
> +		sigabrt();
> +	}
> +}
> +
> +static void xwrite_byte(int fd, char b)
> +{
> +	long ret = sys_write(fd, &b, 1);
> +
> +	if (ret != 1) {
> +		print_failure(__LINE__, "write", ret);
> +		sigabrt();
> +	}
> +}
> +
> +static int xread_byte(int fd)
> +{
> +	char b;
> +	long ret = sys_read(fd, &b, 1);
> +
> +	if (ret != 1) {
> +		print_failure(__LINE__, "read", ret);
> +		sigabrt();
> +	}
> +	return b;
> +}
> +
> +static void xpipe(int fds[static 2])
> +{
> +	long ret = syscall2(__NR_pipe2, (long) fds, O_CLOEXEC);
> +
> +	if (ret != 0) {
> +		print_failure(__LINE__, "pipe2", ret);
> +		sigabrt();
> +	}
> +}
> +
> +static __kernel_pid_t xfork(void)
> +{
> +	long ret = syscall0(__NR_fork);
> +
> +	if (ret < 0) {
> +		print_failure(__LINE__, "fork", ret);
> +		sigabrt();
> +	}
> +	return ret;
> +}
> +
> +static void xexecve(const char *pathname, char **argv, char **envp)
> +{
> +	long ret;
> +
> +	ret = syscall3(__NR_execve, (long) pathname, (long) argv, (long) envp);
> +	print_failure(__LINE__, "execve", ret);
> +	sigabrt();
> +}
> +
> +static __kernel_pid_t xwaitpid(__kernel_pid_t pid, int *status, int options)
> +{
> +	long ret = syscall4(__NR_wait4, pid, (long) status, options, 0);
> +
> +	if (ret < 0) {
> +		print_failure(__LINE__, "wait4", ret);
> +		sigabrt();
> +	}
> +	return ret;
> +}
> +
> +/*
> + * Various helpers.
> + */
> +
> +static void vsyscall_disable(void)
> +{
> +	long ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 0);
> +
> +	if (ret != 0)
> +		print_failure(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 0)", ret);
> +}
> +
> +static void vsyscall_enable(void)
> +{
> +	long ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 1);
> +
> +	if (ret != 0)
> +		print_failure(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 1)", ret);
> +}
> +
> +static long difftime(struct timeval first, struct timeval second)
> +{
> +	return second.tv_usec - first.tv_usec +
> +		(second.tv_sec - first.tv_sec) * 1000 * 1000;
> +}
> +
> +static void ensure_proc_is_mounted(int *status)
> +{
> +	int ret;
> +
> +	if (sys_access("/proc/version", 0) == 0)
> +		return;
> +
> +	ret = sys_mkdir("/proc", 0555);
> +	if (ret == EEXIST)
> +		return;
> +	if (ret != 0) {
> +		print_failure(__LINE__, "could not create /proc", ret);
> +		*status = 1;
> +		return;
> +	}
> +	ret = sys_mount("none", "/proc", "proc", 0, NULL);
> +	if (ret != 0) {
> +		print_failure(__LINE__, "could not mount /proc", ret);
> +		*status = 1;
> +		return;
> +	}
> +	if (sys_access("/proc/version", 0) != 0) {
> +		print_error(__LINE__, "no /proc/version after mounting /proc");
> +		*status = 1;
> +		return;
> +	}
> +}
> +
> +/*
> + * Individual subtest functions.
> + */
> +
> +static void check_time(int *status)
> +{
> +	struct timeval initial_time = { -1, -1 };
> +	struct timeval vsyscall_time = { -1, -1 };
> +	struct timeval final_time = { -1, -1 };
> +	long vsyscall_diff, final_diff;
> +
> +	xgettimeofday(&initial_time);
> +	xvgettimeofday(&vsyscall_time);
> +	xgettimeofday(&final_time);
> +	vsyscall_diff = difftime(initial_time, vsyscall_time);
> +	final_diff = difftime(vsyscall_time, final_time);
> +
> +	print_time(__LINE__, "initial gettimeofday", initial_time);
> +	print_time(__LINE__, "vsyscall gettimeofday", vsyscall_time);
> +	print_time(__LINE__, "final gettimeofday", final_time);
> +
> +	if (initial_time.tv_sec < 0 || initial_time.tv_usec < 0 ||
> +	    vsyscall_time.tv_sec < 0 || vsyscall_time.tv_usec < 0 ||
> +	    final_time.tv_sec < 0 || final_time.tv_usec < 0) {
> +		print_error(__LINE__, "negative time\n");
> +		*status = 1;
> +	}
> +
> +	print_info(__LINE__, "differences: ");
> +	print_signed_dec(vsyscall_diff);
> +	print_char(' ');
> +	print_signed_dec(final_diff);
> +	print_char('\n');
> +
> +	if (vsyscall_diff < 0 || final_diff < 0) {
> +		/*
> +		 * This may produce false positives if there is an active NTP.
> +		 */
> +		print_error(__LINE__, "time went backwards\n");
> +		*status = 1;
> +	}
> +}
> +
> +static void check_lockout_after_fork(int *status, int twice)
> +{
> +	__kernel_pid_t pid;
> +	struct timeval vsyscall_time;
> +	int wstatus;
> +
> +	if (twice) {
> +		__kernel_pid_t pid_outer;
> +
> +		print_info(__LINE__, "checking that lockout is inherited by fork\n");
> +
> +		pid_outer = xfork();
> +		if (pid_outer == 0) {
> +			vsyscall_disable();
> +			/*
> +			 * Logic for the subprocess follows below.
> +			 */
> +		} else {
> +			xwaitpid(pid_outer, &wstatus, 0);
> +			if (wstatus != 0) {
> +				print_error(__LINE__, "unexpected exit status: ");
> +				print_signed_dec(wstatus);
> +				print_char('\n');
> +				*status = 1;
> +			}
> +			return;
> +		}
> +	} else
> +		print_info(__LINE__, "checking that lockout works after one fork\n");
> +
> +	pid = xfork();
> +	if (pid == 0) {
> +		if (!twice)
> +			vsyscall_disable();
> +		/*
> +		 * This should trigger a fault.
> +		 */
> +		xvgettimeofday(&vsyscall_time);
> +		sys_exit(0);
> +	}
> +	xwaitpid(pid, &wstatus, 0);
> +	switch (wstatus) {
> +	case 0:
> +		print_error(__LINE__, "no crash after lockout\n");
> +		*status = 1;
> +		break;
> +	case 0x0100:
> +		*status = 1;
> +		break;
> +	case SIGSEGV:
> +		print_info(__LINE__, "termination after lockout\n");
> +		break;
> +	default:
> +		print_error(__LINE__, "unexpected exit status: ");
> +		print_signed_dec(wstatus);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +
> +	if (twice)
> +		sys_exit(*status);
> +
> +	/*
> +	 * Status in the parent process should be unaffected.
> +	 */
> +	xvgettimeofday(&vsyscall_time);
> +}
> +
> +static void check_no_lockout_after_enable(int *status)
> +{
> +	__kernel_pid_t pid;
> +	struct timeval vsyscall_time;
> +	int wstatus;
> +
> +	print_info(__LINE__, "checking that vsyscall can be re-enabled\n");
> +
> +	pid = xfork();
> +	if (pid == 0) {
> +		vsyscall_disable();
> +		vsyscall_enable();
> +		xvgettimeofday(&vsyscall_time);
> +		print_time(__LINE__, "vsyscall time after re-enable", vsyscall_time);
> +		sys_exit(0);
> +	}
> +
> +	xwaitpid(pid, &wstatus, 0);
> +	if (wstatus != 0) {
> +		print_error(__LINE__, "unexpected exit status: ");
> +		print_signed_dec(wstatus);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +}
> +
> +static void check_no_lockout_after_execve(char **argv, int *status)
> +{
> +	__kernel_pid_t pid;
> +	int wstatus;
> +
> +	print_info(__LINE__, "checking that lockout is not inherited by execve\n");
> +	pid = xfork();
> +	if (pid == 0) {
> +		struct timeval vsyscall_time;
> +		char *new_argv[3];
> +
> +		xvgettimeofday(&vsyscall_time);
> +		vsyscall_disable();
> +
> +		/*
> +		 * Re-exec the second stage.  See main_2 below.
> +		 */
> +		new_argv[0] = argv[0];
> +		new_argv[1] = "2";
> +		new_argv[2] = NULL;
> +		xexecve(argv[0], new_argv, new_argv + 2);
> +	}
> +
> +	xwaitpid(pid, &wstatus, 0);
> +	if (wstatus != 0) {
> +		print_error(__LINE__, "unexpected exit status: ");
> +		print_signed_dec(wstatus);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +}
> +
> +static int has_vsyscall_map(int pid, int *status)
> +{
> +	int result = 0;
> +	char maps_path[50];
> +	int fd;
> +
> +	/*
> +	 * Construct /proc/PID/maps path.
> +	 */
> +	{
> +		struct buffer b;
> +
> +		buffer_init(&b, maps_path, sizeof(maps_path));
> +		buffer_append_string(&b, "/proc/");
> +		if (pid == 0)
> +			buffer_append_string(&b, "self");
> +		else
> +			buffer_append_dec(&b, pid);
> +		buffer_append_string(&b, "/maps");
> +		buffer_append(&b, 0);
> +	}
> +
> +	fd = sys_open(maps_path, O_RDONLY, 0);
> +	if (fd < 0) {
> +		print_error(__LINE__, "maps file ");
> +		print_string(maps_path);
> +		print_string(": ");
> +		print_signed_dec(fd);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +
> +	/*
> +	 * Search for "[vsyscall]\n".
> +	 */
> +	{
> +		char buf[4096];
> +		long ret;
> +
> +		for (size_t i = 0; i < sizeof(buf); ++i)
> +			buf[i] = 0;
> +		ret = sys_read(fd, buf, sizeof(buf));
> +
> +		if (ret < 0 || ret >= sizeof(buf))
> +			print_failure(__LINE__, "read", ret);
> +		else {
> +			char *bracket = buf;
> +
> +			while (1) {
> +				while (*bracket && *bracket != '[')
> +					++bracket;
> +				if (*bracket != '[')
> +					/*
> +					 * End of file has been reached.
> +					 */
> +					break;
> +				++bracket;
> +				if (bracket[0] == 'v'
> +				    && bracket[1] == 's'
> +				    && bracket[2] == 'y'
> +				    && bracket[3] == 's'
> +				    && bracket[4] == 'c'
> +				    && bracket[5] == 'a'
> +				    && bracket[6] == 'l'
> +				    && bracket[7] == 'l'
> +				    && bracket[8] == ']'
> +				    && bracket[9] == '\n') {
> +					result = 1;
> +					break;
> +				}
> +			}
> +		}
> +	}
> +
> +	xclose(fd);
> +	return result;
> +}
> +
> +static void check_vsyscall_in_self_maps(int *status)
> +{
> +	__kernel_pid_t pid;
> +	int wstatus;
> +
> +	print_info(__LINE__, "checking [vsyscall] in /proc/self/maps\n");
> +
> +	pid = xfork();
> +	if (pid == 0) {
> +		if (!has_vsyscall_map(0, status)) {
> +			print_error(__LINE__, "[vsyscall] missing\n");
> +			*status = 1;
> +		}
> +		vsyscall_disable();
> +		if (has_vsyscall_map(0, status)) {
> +			print_error(__LINE__, "[vsyscall] present after disable\n");
> +			*status = 1;
> +		}
> +		vsyscall_enable();
> +		if (!has_vsyscall_map(0, status)) {
> +			print_error(__LINE__, "[vsyscall] missing after enable\n");
> +			*status = 1;
> +		}
> +		sys_exit(*status);
> +	}
> +
> +	xwaitpid(pid, &wstatus, 0);
> +	if (wstatus != 0) {
> +		print_error(__LINE__, "unexpected exit status: ");
> +		print_signed_dec(wstatus);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +}
> +
> +static void check_vsyscall_maps_for_subprocess(int *status)
> +{
> +	__kernel_pid_t pid;
> +	int wstatus;
> +	int outer_to_inner[2];
> +	int inner_to_outer[2];
> +
> +	/*
> +	 * Create pipes used to synchronize the two processes.
> +	 */
> +	xpipe(outer_to_inner);
> +	xpipe(inner_to_outer);
> +
> +	print_info(__LINE__, "checking [vsyscall] in /proc/PID/maps\n");
> +
> +	pid = xfork();
> +	if (pid == 0) {
> +		xclose(outer_to_inner[1]);
> +		xclose(inner_to_outer[0]);
> +
> +		xread_byte(outer_to_inner[0]);
> +		vsyscall_disable();
> +		xwrite_byte(inner_to_outer[1], 101);
> +
> +		xread_byte(outer_to_inner[0]);
> +		vsyscall_disable();
> +		xwrite_byte(inner_to_outer[1], 102);
> +
> +		sys_exit(0);
> +	}
> +
> +	xclose(outer_to_inner[0]);
> +	xclose(inner_to_outer[1]);
> +
> +	if (!has_vsyscall_map(pid, status)) {
> +		print_error(__LINE__, "subprocess starts without [vsyscall]");
> +		*status = 1;
> +	}
> +
> +	xwrite_byte(outer_to_inner[1], 1);
> +	xread_byte(inner_to_outer[0]);
> +
> +	if (has_vsyscall_map(pid, status)) {
> +		print_error(__LINE__, "subprocess has [vsyscall] after disable");
> +		*status = 1;
> +	}
> +
> +	xwrite_byte(outer_to_inner[1], 2);
> +	xread_byte(inner_to_outer[0]);
> +
> +	if (has_vsyscall_map(pid, status)) {
> +		print_error(__LINE__, "subprocess lacks [vsyscall] after enable");
> +		*status = 1;
> +	}
> +
> +	xclose(outer_to_inner[1]);
> +	xclose(inner_to_outer[0]);
> +
> +	xwaitpid(pid, &wstatus, 0);
> +	if (wstatus != 0) {
> +		print_error(__LINE__, "unexpected exit status: ");
> +		print_signed_dec(wstatus);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +}
> +
> +static void check_einval(int *status)
> +{
> +	long ret;
> +
> +	ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 2);
> +	if (ret != -EINVAL) {
> +		print_error(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 2) returned ");
> +		print_signed_dec(ret);
> +		print_char('\n');
> +		*status = 1;
> +	}
> +}
> +
> +/*
> + * Second stage: Check that the lockout is not inherited across execve.
> + * Used from check_no_lockout_after_execve.
> + */
> +static int main_2(void)
> +{
> +	struct timeval vsyscall_time = { -1, -1 };
> +	int status = 0;
> +
> +	xvgettimeofday(&vsyscall_time);
> +	print_time(__LINE__, "vsyscall gettimeofday after fork", vsyscall_time);
> +	if (vsyscall_time.tv_sec < 0 || vsyscall_time.tv_usec < 0)
> +		status = 1;
> +
> +	return status;
> +}
> +
> +static int main(int argc, char **argv)
> +{
> +	int status = 0;
> +
> +	if (argc > 1) {
> +		switch (*argv[1]) {
> +		case '2':
> +			return main_2();
> +		default:
> +			print_string("usage: ");
> +			print_string(argv[0]);
> +			print_string("\n");
> +			return 1;
> +		}
> +	}
> +
> +	ensure_proc_is_mounted(&status);
> +
> +	if (has_vsyscall_map(0, &status))
> +		print_info(__LINE__, "vsyscall active at process start\n");
> +	else
> +		print_error(__LINE__, "vsyscall inactive at process start\n");
> +
> +
> +	check_time(&status);
> +	check_lockout_after_fork(&status, 0);
> +	check_lockout_after_fork(&status, 1);
> +	check_no_lockout_after_enable(&status);
> +	check_no_lockout_after_execve(argv, &status);
> +	check_vsyscall_in_self_maps(&status);
> +	check_vsyscall_maps_for_subprocess(&status);
> +	check_einval(&status);
> +
> +	print_info(__LINE__, "testing done, exit status: ");
> +	print_signed_dec(status);
> +	print_char('\n');
> +	return status;
> +}
> +
> +static void __attribute__ ((used)) main_trampoline(long *rsp)
> +{
> +	sys_exit(main(*rsp, (char **) (rsp + 1)));
> +}
> +
> +__asm__(".text\n\t"
> +	".globl _start\n"
> +	"_start:\n\t"
> +	".cfi_startproc\n\t"
> +	".cfi_undefined rip\n\t"
> +	"movq %rsp, %rdi\n\t"
> +	"callq main_trampoline\n\t" /* Results in psABI %rsp alignment.  */
> +	".cfi_endproc\n\t"
> +	".type _start, @function\n\t"
> +	".size _start, . - _start\n\t"
> +	".previous");

Florian Weimer Jan. 13, 2022, 9:57 p.m. UTC | #2

* Andy Lutomirski:

> On 1/5/22 08:03, Florian Weimer wrote:
>> Signed-off-by: Florian Weimer <[e-mail]>
>
> This seems like a respectable test case, but why does it work so hard
> to avoid using libc?

Back when this was still a true lockout and not a toggle, it was
necessary to bypass the startup code, so that the test still works once
the (g)libc startup starts activating the lockout.  The /proc mounting
is there to support running as init in a VM (which makes development so
much easier).

I could ditch the /proc mounting, perform some limited data gathering in
a pre-_start routine, undo a potential lockout before the tests, and
then use libc functions for the actual test.  It would probably be a bit
less code (printf is nice), but I'd probably have to use direct system
calls for the early data gathering anyway, so those parts would still be
there.

Thanks,
Florian

Patch

diff --git a/tools/arch/x86/include/uapi/asm/prctl.h b/tools/arch/x86/include/uapi/asm/prctl.h
index 754a07856817..aad0bcfbf49f 100644
--- a/tools/arch/x86/include/uapi/asm/prctl.h
+++ b/tools/arch/x86/include/uapi/asm/prctl.h
@@ -18,4 +18,6 @@ 
 #define ARCH_MAP_VDSO_32	0x2002
 #define ARCH_MAP_VDSO_64	0x2003
 
+#define ARCH_VSYSCALL_CONTROL	0x5001
+
 #endif /* _ASM_X86_PRCTL_H */
diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 0993d12f2c38..4c751836bfeb 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -18,7 +18,7 @@  TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \
 			test_FCMOV test_FCOMI test_FISTTP \
 			vdso_restorer
 TARGETS_C_64BIT_ONLY := fsgsbase sysret_rip syscall_numbering \
-			corrupt_xstate_header amx
+			corrupt_xstate_header amx vsyscall_control
 # Some selftests require 32bit support enabled also on 64bit systems
 TARGETS_C_32BIT_NEEDED := ldt_gdt ptrace_syscall
 
@@ -107,3 +107,8 @@  $(OUTPUT)/test_syscall_vdso_32: thunks_32.S
 # state.
 $(OUTPUT)/check_initial_reg_state_32: CFLAGS += -Wl,-ereal_start -static
 $(OUTPUT)/check_initial_reg_state_64: CFLAGS += -Wl,-ereal_start -static
+
+# This test does not link against anything (neither libc nor libgcc).
+$(OUTPUT)/vsyscall_control_64: \
+	LIBS := -Wl,-no-pie -static -nostdlib -nostartfiles
+	CFLAGS += -fno-pie -fno-stack-protector -fno-builtin -ffreestanding
diff --git a/tools/testing/selftests/x86/vsyscall_control.c b/tools/testing/selftests/x86/vsyscall_control.c
new file mode 100644
index 000000000000..ee966f936c89
--- /dev/null
+++ b/tools/testing/selftests/x86/vsyscall_control.c
@@ -0,0 +1,891 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * vsyscall_lockout.c - check that disabling vsyscall works
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * This test requires vsyscall=xonly or vsyscall=emulate.  With
+ * vsyscall=emulate, ARCH_VSYSCALL_CONTROL cannot turn off vsyscall
+ * completely (reads still work), but this is not tested here.
+ */
+
+#include <stddef.h>
+
+#include <asm/prctl.h>
+#include <asm/vsyscall.h>
+#include <linux/errno.h>
+#include <linux/fcntl.h>
+#include <linux/signal.h>
+#include <linux/time.h>
+#include <linux/types.h>
+#include <linux/unistd.h>
+
+#ifndef ARCH_VSYSCALL_CONTROL
+#define ARCH_VSYSCALL_CONTROL	0x5001
+#elif ARCH_VSYSCALL_CONTROL != 0x5001
+#error wrong vlaue for ARCH_VSYSCALL_CONTROL
+#endif
+
+
+static inline long syscall0(int nr)
+{
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall1(int nr, long arg0)
+{
+	register long rdi asm("rdi") = arg0;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall2(int nr, long arg0, long arg1)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall3(int nr, long arg0, long arg1, long arg2)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	register long rdx asm("rdx") = arg2;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall4(int nr, long arg0, long arg1, long arg2, long arg3)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	register long rdx asm("rdx") = arg2;
+	register long r10 asm("r10") = arg3;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx),
+			    "r" (r10)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long syscall5(int nr, long arg0, long arg1, long arg2, long arg3,
+			    long arg4)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	register long rdx asm("rdx") = arg2;
+	register long r10 asm("r10") = arg3;
+	register long r8 asm("r8") = arg4;
+	unsigned long result;
+
+	__asm__ volatile ("syscall"
+			  : "=a" (result)
+			  : "0" (nr), "r" (rdi), "r" (rsi), "r" (rdx),
+			    "r" (r10), "r" (r8)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static inline long vsyscall2(long addr, long arg0, long arg1)
+{
+	register long rdi asm("rdi") = arg0;
+	register long rsi asm("rsi") = arg1;
+	unsigned long result;
+
+	__asm__ volatile ("callq *%%rax"
+			  : "=a" (result)
+			  : "0" (addr), "r" (rdi), "r" (rsi)
+			  : "memory", "cc", "r11", "cx");
+	return result;
+}
+
+static void __attribute__ ((noreturn)) sys_exit(int status)
+{
+	syscall1(__NR_exit, status);
+	__builtin_unreachable();
+}
+
+static int sys_access(const char *pathname, int mode)
+{
+	return syscall2(__NR_access, (long) pathname, mode);
+}
+
+static int sys_mkdir(const char *pathname, __kernel_mode_t mode)
+{
+	return syscall2(__NR_mkdir, (long) pathname, mode);
+}
+
+static int sys_open(const char *pathname, int flags, __kernel_mode_t mode)
+{
+	return syscall3(__NR_open, (long) pathname, flags, mode);
+}
+
+static long sys_read(int fd, void *buffer, size_t length)
+{
+	return syscall3(__NR_read, fd, (long) buffer, length);
+}
+
+static long sys_write(int fd, const void *buffer, size_t length)
+{
+	return syscall3(__NR_write, fd, (long) buffer, length);
+}
+
+static int sys_mount(const char *source, const char *pathname,
+		     const char *fstype, unsigned long flags,
+		     const void *data)
+{
+	return syscall5(__NR_mount, (long) source, (long) pathname,
+			(long) fstype, flags, (long) data);
+}
+
+static void sigabrt(void)
+{
+	syscall2(__NR_kill, syscall0(__NR_getpid), SIGABRT);
+}
+
+/*
+ * String buffers.
+ */
+
+struct buffer {
+	char *position;
+	char *limit;
+};
+
+static void buffer_init(struct buffer *b, char *start, size_t length)
+{
+	b->position = start;
+	b->limit = start + length;
+}
+
+static void buffer_append(struct buffer *b, char ch)
+{
+	if (b->position >= b->limit)
+		sigabrt();
+	*b->position = ch;
+	++b->position;
+}
+
+static void buffer_append_string(struct buffer *b, const char *p)
+{
+	while (*p) {
+		buffer_append(b, *p);
+		++p;
+	}
+}
+
+static void buffer_append_dec_1(struct buffer *b, unsigned long val)
+{
+	if (val != 0) {
+		buffer_append_dec_1(b, val / 10);
+		buffer_append(b, '0' + (val % 10));
+	}
+}
+
+static void buffer_append_dec(struct buffer *b, unsigned long val)
+{
+	if (val == 0) {
+		buffer_append(b, '0');
+		return;
+	}
+	buffer_append_dec_1(b, val);
+}
+
+/*
+ * Output to standard output.
+ */
+
+static void print_char(char byte)
+{
+	if (sys_write(1, &byte, 1) < 0)
+		sigabrt();
+}
+
+static void print_string(const char *p)
+{
+	while (*p) {
+		print_char(*p);
+		++p;
+	}
+}
+
+static void print_dec_1(unsigned long val)
+{
+	if (val != 0) {
+		print_dec_1(val / 10);
+		print_char('0' + (val % 10));
+	}
+}
+
+static void print_dec(unsigned long val)
+{
+	if (val == 0)
+		print_char('0');
+	else
+		print_dec_1(val);
+}
+
+static void print_signed_dec(long val)
+{
+	if (val < 0) {
+		print_char('-');
+		print_dec(-(unsigned long)val);
+	} else
+		print_dec(val);
+}
+
+static void print_message(unsigned int lineno, const char *tag, const char *p)
+{
+	print_string(__FILE__);
+	print_char(':');
+	print_dec(lineno);
+	print_char(':');
+	print_char(' ');
+	print_string(tag);
+	print_char(':');
+	print_char(' ');
+	print_string(p);
+}
+
+static void print_info(unsigned int lineno, const char *p)
+{
+	print_message(lineno, "info", p);
+}
+
+static void print_error(unsigned int lineno, const char *p)
+{
+	print_message(lineno, "ERROR", p);
+}
+
+static void print_failure(int lineno, const char *label, long ret)
+{
+	print_error(lineno, label);
+	print_string(" failed: ");
+	print_signed_dec(ret);
+	print_char('\n');
+}
+
+static void print_time(int lineno, const char *label, struct timeval tv)
+{
+	print_info(lineno, label);
+	print_string(": ");
+	print_dec(tv.tv_sec);
+	print_char(' ');
+	print_dec(tv.tv_usec);
+	print_char('\n');
+}
+
+/*
+ * Process-failing (v)syscall wrappers.
+ */
+
+static void xgettimeofday(struct timeval *tv)
+{
+	long ret = syscall2(__NR_gettimeofday, (long) tv, 0);
+
+	if (ret != 0) {
+		print_failure(__LINE__, "gettimeofday", ret);
+		sigabrt();
+	}
+}
+
+static void xvgettimeofday(struct timeval *tv)
+{
+	long ret = vsyscall2(VSYSCALL_ADDR, (long) tv, 0);
+
+	if (ret) {
+		print_failure(__LINE__, "vgettimeofday", ret);
+		sigabrt();
+	}
+}
+
+static int sys_arch_prctl(int code, unsigned long addr)
+{
+	return syscall2(__NR_arch_prctl, code, addr);
+}
+
+static void xclose(int fd)
+{
+	long ret = syscall1(__NR_close, fd);
+
+	if (ret < 0) {
+		print_failure(__LINE__, "close", ret);
+		sigabrt();
+	}
+}
+
+static void xwrite_byte(int fd, char b)
+{
+	long ret = sys_write(fd, &b, 1);
+
+	if (ret != 1) {
+		print_failure(__LINE__, "write", ret);
+		sigabrt();
+	}
+}
+
+static int xread_byte(int fd)
+{
+	char b;
+	long ret = sys_read(fd, &b, 1);
+
+	if (ret != 1) {
+		print_failure(__LINE__, "read", ret);
+		sigabrt();
+	}
+	return b;
+}
+
+static void xpipe(int fds[static 2])
+{
+	long ret = syscall2(__NR_pipe2, (long) fds, O_CLOEXEC);
+
+	if (ret != 0) {
+		print_failure(__LINE__, "pipe2", ret);
+		sigabrt();
+	}
+}
+
+static __kernel_pid_t xfork(void)
+{
+	long ret = syscall0(__NR_fork);
+
+	if (ret < 0) {
+		print_failure(__LINE__, "fork", ret);
+		sigabrt();
+	}
+	return ret;
+}
+
+static void xexecve(const char *pathname, char **argv, char **envp)
+{
+	long ret;
+
+	ret = syscall3(__NR_execve, (long) pathname, (long) argv, (long) envp);
+	print_failure(__LINE__, "execve", ret);
+	sigabrt();
+}
+
+static __kernel_pid_t xwaitpid(__kernel_pid_t pid, int *status, int options)
+{
+	long ret = syscall4(__NR_wait4, pid, (long) status, options, 0);
+
+	if (ret < 0) {
+		print_failure(__LINE__, "wait4", ret);
+		sigabrt();
+	}
+	return ret;
+}
+
+/*
+ * Various helpers.
+ */
+
+static void vsyscall_disable(void)
+{
+	long ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 0);
+
+	if (ret != 0)
+		print_failure(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 0)", ret);
+}
+
+static void vsyscall_enable(void)
+{
+	long ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 1);
+
+	if (ret != 0)
+		print_failure(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 1)", ret);
+}
+
+static long difftime(struct timeval first, struct timeval second)
+{
+	return second.tv_usec - first.tv_usec +
+		(second.tv_sec - first.tv_sec) * 1000 * 1000;
+}
+
+static void ensure_proc_is_mounted(int *status)
+{
+	int ret;
+
+	if (sys_access("/proc/version", 0) == 0)
+		return;
+
+	ret = sys_mkdir("/proc", 0555);
+	if (ret == EEXIST)
+		return;
+	if (ret != 0) {
+		print_failure(__LINE__, "could not create /proc", ret);
+		*status = 1;
+		return;
+	}
+	ret = sys_mount("none", "/proc", "proc", 0, NULL);
+	if (ret != 0) {
+		print_failure(__LINE__, "could not mount /proc", ret);
+		*status = 1;
+		return;
+	}
+	if (sys_access("/proc/version", 0) != 0) {
+		print_error(__LINE__, "no /proc/version after mounting /proc");
+		*status = 1;
+		return;
+	}
+}
+
+/*
+ * Individual subtest functions.
+ */
+
+static void check_time(int *status)
+{
+	struct timeval initial_time = { -1, -1 };
+	struct timeval vsyscall_time = { -1, -1 };
+	struct timeval final_time = { -1, -1 };
+	long vsyscall_diff, final_diff;
+
+	xgettimeofday(&initial_time);
+	xvgettimeofday(&vsyscall_time);
+	xgettimeofday(&final_time);
+	vsyscall_diff = difftime(initial_time, vsyscall_time);
+	final_diff = difftime(vsyscall_time, final_time);
+
+	print_time(__LINE__, "initial gettimeofday", initial_time);
+	print_time(__LINE__, "vsyscall gettimeofday", vsyscall_time);
+	print_time(__LINE__, "final gettimeofday", final_time);
+
+	if (initial_time.tv_sec < 0 || initial_time.tv_usec < 0 ||
+	    vsyscall_time.tv_sec < 0 || vsyscall_time.tv_usec < 0 ||
+	    final_time.tv_sec < 0 || final_time.tv_usec < 0) {
+		print_error(__LINE__, "negative time\n");
+		*status = 1;
+	}
+
+	print_info(__LINE__, "differences: ");
+	print_signed_dec(vsyscall_diff);
+	print_char(' ');
+	print_signed_dec(final_diff);
+	print_char('\n');
+
+	if (vsyscall_diff < 0 || final_diff < 0) {
+		/*
+		 * This may produce false positives if there is an active NTP.
+		 */
+		print_error(__LINE__, "time went backwards\n");
+		*status = 1;
+	}
+}
+
+static void check_lockout_after_fork(int *status, int twice)
+{
+	__kernel_pid_t pid;
+	struct timeval vsyscall_time;
+	int wstatus;
+
+	if (twice) {
+		__kernel_pid_t pid_outer;
+
+		print_info(__LINE__, "checking that lockout is inherited by fork\n");
+
+		pid_outer = xfork();
+		if (pid_outer == 0) {
+			vsyscall_disable();
+			/*
+			 * Logic for the subprocess follows below.
+			 */
+		} else {
+			xwaitpid(pid_outer, &wstatus, 0);
+			if (wstatus != 0) {
+				print_error(__LINE__, "unexpected exit status: ");
+				print_signed_dec(wstatus);
+				print_char('\n');
+				*status = 1;
+			}
+			return;
+		}
+	} else
+		print_info(__LINE__, "checking that lockout works after one fork\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		if (!twice)
+			vsyscall_disable();
+		/*
+		 * This should trigger a fault.
+		 */
+		xvgettimeofday(&vsyscall_time);
+		sys_exit(0);
+	}
+	xwaitpid(pid, &wstatus, 0);
+	switch (wstatus) {
+	case 0:
+		print_error(__LINE__, "no crash after lockout\n");
+		*status = 1;
+		break;
+	case 0x0100:
+		*status = 1;
+		break;
+	case SIGSEGV:
+		print_info(__LINE__, "termination after lockout\n");
+		break;
+	default:
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+
+	if (twice)
+		sys_exit(*status);
+
+	/*
+	 * Status in the parent process should be unaffected.
+	 */
+	xvgettimeofday(&vsyscall_time);
+}
+
+static void check_no_lockout_after_enable(int *status)
+{
+	__kernel_pid_t pid;
+	struct timeval vsyscall_time;
+	int wstatus;
+
+	print_info(__LINE__, "checking that vsyscall can be re-enabled\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		vsyscall_disable();
+		vsyscall_enable();
+		xvgettimeofday(&vsyscall_time);
+		print_time(__LINE__, "vsyscall time after re-enable", vsyscall_time);
+		sys_exit(0);
+	}
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static void check_no_lockout_after_execve(char **argv, int *status)
+{
+	__kernel_pid_t pid;
+	int wstatus;
+
+	print_info(__LINE__, "checking that lockout is not inherited by execve\n");
+	pid = xfork();
+	if (pid == 0) {
+		struct timeval vsyscall_time;
+		char *new_argv[3];
+
+		xvgettimeofday(&vsyscall_time);
+		vsyscall_disable();
+
+		/*
+		 * Re-exec the second stage.  See main_2 below.
+		 */
+		new_argv[0] = argv[0];
+		new_argv[1] = "2";
+		new_argv[2] = NULL;
+		xexecve(argv[0], new_argv, new_argv + 2);
+	}
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static int has_vsyscall_map(int pid, int *status)
+{
+	int result = 0;
+	char maps_path[50];
+	int fd;
+
+	/*
+	 * Construct /proc/PID/maps path.
+	 */
+	{
+		struct buffer b;
+
+		buffer_init(&b, maps_path, sizeof(maps_path));
+		buffer_append_string(&b, "/proc/");
+		if (pid == 0)
+			buffer_append_string(&b, "self");
+		else
+			buffer_append_dec(&b, pid);
+		buffer_append_string(&b, "/maps");
+		buffer_append(&b, 0);
+	}
+
+	fd = sys_open(maps_path, O_RDONLY, 0);
+	if (fd < 0) {
+		print_error(__LINE__, "maps file ");
+		print_string(maps_path);
+		print_string(": ");
+		print_signed_dec(fd);
+		print_char('\n');
+		*status = 1;
+	}
+
+	/*
+	 * Search for "[vsyscall]\n".
+	 */
+	{
+		char buf[4096];
+		long ret;
+
+		for (size_t i = 0; i < sizeof(buf); ++i)
+			buf[i] = 0;
+		ret = sys_read(fd, buf, sizeof(buf));
+
+		if (ret < 0 || ret >= sizeof(buf))
+			print_failure(__LINE__, "read", ret);
+		else {
+			char *bracket = buf;
+
+			while (1) {
+				while (*bracket && *bracket != '[')
+					++bracket;
+				if (*bracket != '[')
+					/*
+					 * End of file has been reached.
+					 */
+					break;
+				++bracket;
+				if (bracket[0] == 'v'
+				    && bracket[1] == 's'
+				    && bracket[2] == 'y'
+				    && bracket[3] == 's'
+				    && bracket[4] == 'c'
+				    && bracket[5] == 'a'
+				    && bracket[6] == 'l'
+				    && bracket[7] == 'l'
+				    && bracket[8] == ']'
+				    && bracket[9] == '\n') {
+					result = 1;
+					break;
+				}
+			}
+		}
+	}
+
+	xclose(fd);
+	return result;
+}
+
+static void check_vsyscall_in_self_maps(int *status)
+{
+	__kernel_pid_t pid;
+	int wstatus;
+
+	print_info(__LINE__, "checking [vsyscall] in /proc/self/maps\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		if (!has_vsyscall_map(0, status)) {
+			print_error(__LINE__, "[vsyscall] missing\n");
+			*status = 1;
+		}
+		vsyscall_disable();
+		if (has_vsyscall_map(0, status)) {
+			print_error(__LINE__, "[vsyscall] present after disable\n");
+			*status = 1;
+		}
+		vsyscall_enable();
+		if (!has_vsyscall_map(0, status)) {
+			print_error(__LINE__, "[vsyscall] missing after enable\n");
+			*status = 1;
+		}
+		sys_exit(*status);
+	}
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static void check_vsyscall_maps_for_subprocess(int *status)
+{
+	__kernel_pid_t pid;
+	int wstatus;
+	int outer_to_inner[2];
+	int inner_to_outer[2];
+
+	/*
+	 * Create pipes used to synchronize the two processes.
+	 */
+	xpipe(outer_to_inner);
+	xpipe(inner_to_outer);
+
+	print_info(__LINE__, "checking [vsyscall] in /proc/PID/maps\n");
+
+	pid = xfork();
+	if (pid == 0) {
+		xclose(outer_to_inner[1]);
+		xclose(inner_to_outer[0]);
+
+		xread_byte(outer_to_inner[0]);
+		vsyscall_disable();
+		xwrite_byte(inner_to_outer[1], 101);
+
+		xread_byte(outer_to_inner[0]);
+		vsyscall_disable();
+		xwrite_byte(inner_to_outer[1], 102);
+
+		sys_exit(0);
+	}
+
+	xclose(outer_to_inner[0]);
+	xclose(inner_to_outer[1]);
+
+	if (!has_vsyscall_map(pid, status)) {
+		print_error(__LINE__, "subprocess starts without [vsyscall]");
+		*status = 1;
+	}
+
+	xwrite_byte(outer_to_inner[1], 1);
+	xread_byte(inner_to_outer[0]);
+
+	if (has_vsyscall_map(pid, status)) {
+		print_error(__LINE__, "subprocess has [vsyscall] after disable");
+		*status = 1;
+	}
+
+	xwrite_byte(outer_to_inner[1], 2);
+	xread_byte(inner_to_outer[0]);
+
+	if (has_vsyscall_map(pid, status)) {
+		print_error(__LINE__, "subprocess lacks [vsyscall] after enable");
+		*status = 1;
+	}
+
+	xclose(outer_to_inner[1]);
+	xclose(inner_to_outer[0]);
+
+	xwaitpid(pid, &wstatus, 0);
+	if (wstatus != 0) {
+		print_error(__LINE__, "unexpected exit status: ");
+		print_signed_dec(wstatus);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+static void check_einval(int *status)
+{
+	long ret;
+
+	ret = sys_arch_prctl(ARCH_VSYSCALL_CONTROL, 2);
+	if (ret != -EINVAL) {
+		print_error(__LINE__, "arch_prctl(ARCH_VSYSCALL_CONTROL, 2) returned ");
+		print_signed_dec(ret);
+		print_char('\n');
+		*status = 1;
+	}
+}
+
+/*
+ * Second stage: Check that the lockout is not inherited across execve.
+ * Used from check_no_lockout_after_execve.
+ */
+static int main_2(void)
+{
+	struct timeval vsyscall_time = { -1, -1 };
+	int status = 0;
+
+	xvgettimeofday(&vsyscall_time);
+	print_time(__LINE__, "vsyscall gettimeofday after fork", vsyscall_time);
+	if (vsyscall_time.tv_sec < 0 || vsyscall_time.tv_usec < 0)
+		status = 1;
+
+	return status;
+}
+
+static int main(int argc, char **argv)
+{
+	int status = 0;
+
+	if (argc > 1) {
+		switch (*argv[1]) {
+		case '2':
+			return main_2();
+		default:
+			print_string("usage: ");
+			print_string(argv[0]);
+			print_string("\n");
+			return 1;
+		}
+	}
+
+	ensure_proc_is_mounted(&status);
+
+	if (has_vsyscall_map(0, &status))
+		print_info(__LINE__, "vsyscall active at process start\n");
+	else
+		print_error(__LINE__, "vsyscall inactive at process start\n");
+
+
+	check_time(&status);
+	check_lockout_after_fork(&status, 0);
+	check_lockout_after_fork(&status, 1);
+	check_no_lockout_after_enable(&status);
+	check_no_lockout_after_execve(argv, &status);
+	check_vsyscall_in_self_maps(&status);
+	check_vsyscall_maps_for_subprocess(&status);
+	check_einval(&status);
+
+	print_info(__LINE__, "testing done, exit status: ");
+	print_signed_dec(status);
+	print_char('\n');
+	return status;
+}
+
+static void __attribute__ ((used)) main_trampoline(long *rsp)
+{
+	sys_exit(main(*rsp, (char **) (rsp + 1)));
+}
+
+__asm__(".text\n\t"
+	".globl _start\n"
+	"_start:\n\t"
+	".cfi_startproc\n\t"
+	".cfi_undefined rip\n\t"
+	"movq %rsp, %rdi\n\t"
+	"callq main_trampoline\n\t" /* Results in psABI %rsp alignment.  */
+	".cfi_endproc\n\t"
+	".type _start, @function\n\t"
+	".size _start, . - _start\n\t"
+	".previous");