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/*
* 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;
}
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