selftests/x86: Add vDSO mremap() test

.PHONY: all all_32 all_64 warn_32bit_failure clean

TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall \

TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt ptrace_syscall test_mremap_vdso \

			check_initial_reg_state sigreturn ldt_gdt iopl

TARGETS_C_32BIT_ONLY := entry_from_vm86 syscall_arg_fault test_syscall_vdso unwind_vdso \

			test_FCMOV test_FCOMI test_FISTTP \

/*

 * 32-bit test to check vDSO mremap.

 *

 * Copyright (c) 2016 Dmitry Safonov

 * Suggested-by: Andrew Lutomirski

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms and conditions of the GNU General Public License,

 * version 2, as published by the Free Software Foundation.

 *

 * This program is distributed in the hope it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * General Public License for more details.

 */

/*

 * Can be built statically:

 * gcc -Os -Wall -static -m32 test_mremap_vdso.c

 */

#define _GNU_SOURCE

#include <stdio.h>

#include <errno.h>

#include <unistd.h>

#include <string.h>

#include <sys/mman.h>

#include <sys/auxv.h>

#include <sys/syscall.h>

#include <sys/wait.h>

#define PAGE_SIZE	4096

static int try_to_remap(void *vdso_addr, unsigned long size)

{

	void *dest_addr, *new_addr;

	/* Searching for memory location where to remap */

	dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);

	if (dest_addr == MAP_FAILED) {

		printf("[WARN]\tmmap failed (%d): %m\n", errno);

		return 0;

	}

	printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",

		vdso_addr, (unsigned long)vdso_addr + size,

		dest_addr, (unsigned long)dest_addr + size);

	fflush(stdout);

	new_addr = mremap(vdso_addr, size, size,

			MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);

	if ((unsigned long)new_addr == (unsigned long)-1) {

		munmap(dest_addr, size);

		if (errno == EINVAL) {

			printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");

			return -1; /* Retry with larger */

		}

		printf("[FAIL]\tmremap failed (%d): %m\n", errno);

		return 1;

	}

	return 0;

}

int main(int argc, char **argv, char **envp)

{

	pid_t child;

	child = fork();

	if (child == -1) {

		printf("[WARN]\tfailed to fork (%d): %m\n", errno);

		return 1;

	}

	if (child == 0) {

		unsigned long vdso_size = PAGE_SIZE;

		unsigned long auxval;

		int ret = -1;

		auxval = getauxval(AT_SYSINFO_EHDR);

		printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);

		if (!auxval || auxval == -ENOENT) {

			printf("[WARN]\tgetauxval failed\n");

			return 0;

		}

		/* Simpler than parsing ELF header */

		while (ret < 0) {

			ret = try_to_remap((void *)auxval, vdso_size);

			vdso_size += PAGE_SIZE;

		}

		/* Glibc is likely to explode now - exit with raw syscall */

		asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));

	} else {

		int status;

		if (waitpid(child, &status, 0) != child ||

			!WIFEXITED(status)) {

			printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");

			return 1;

		} else if (WEXITSTATUS(status) != 0) {

			printf("[FAIL]\tChild failed with %d\n",

					WEXITSTATUS(status));

			return 1;

		}

		printf("[OK]\n");

	}

	return 0;

}