tools/testing/selftests/x86/test_mremap_vdso.c

   1 /*
   2  * 32-bit test to check vDSO mremap.
   3  *
   4  * Copyright (c) 2016 Dmitry Safonov
   5  * Suggested-by: Andrew Lutomirski
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms and conditions of the GNU General Public License,
   9  * version 2, as published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope it will be useful, but
  12  * WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  */
  16 /*
  17  * Can be built statically:
  18  * gcc -Os -Wall -static -m32 test_mremap_vdso.c
  19  */
  20 #define _GNU_SOURCE
  21 #include <stdio.h>
  22 #include <errno.h>
  23 #include <unistd.h>
  24 #include <string.h>
  25
  26 #include <sys/mman.h>
  27 #include <sys/auxv.h>
  28 #include <sys/syscall.h>
  29 #include <sys/wait.h>
  30
  31 #define PAGE_SIZE       4096
  32
  33 static int try_to_remap(void *vdso_addr, unsigned long size)
  34 {
  35         void *dest_addr, *new_addr;
  36
  37         /* Searching for memory location where to remap */
  38         dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  39         if (dest_addr == MAP_FAILED) {
  40                 printf("[WARN]\tmmap failed (%d): %m\n", errno);
  41                 return 0;
  42         }
  43
  44         printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",
  45                 vdso_addr, (unsigned long)vdso_addr + size,
  46                 dest_addr, (unsigned long)dest_addr + size);
  47         fflush(stdout);
  48
  49         new_addr = mremap(vdso_addr, size, size,
  50                         MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
  51         if ((unsigned long)new_addr == (unsigned long)-1) {
  52                 munmap(dest_addr, size);
  53                 if (errno == EINVAL) {
  54                         printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");
  55                         return -1; /* Retry with larger */
  56                 }
  57                 printf("[FAIL]\tmremap failed (%d): %m\n", errno);
  58                 return 1;
  59         }
  60
  61         return 0;
  62
  63 }
  64
  65 int main(int argc, char **argv, char **envp)
  66 {
  67         pid_t child;
  68
  69         child = fork();
  70         if (child == -1) {
  71                 printf("[WARN]\tfailed to fork (%d): %m\n", errno);
  72                 return 1;
  73         }
  74
  75         if (child == 0) {
  76                 unsigned long vdso_size = PAGE_SIZE;
  77                 unsigned long auxval;
  78                 int ret = -1;
  79
  80                 auxval = getauxval(AT_SYSINFO_EHDR);
  81                 printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);
  82                 if (!auxval || auxval == -ENOENT) {
  83                         printf("[WARN]\tgetauxval failed\n");
  84                         return 0;
  85                 }
  86
  87                 /* Simpler than parsing ELF header */
  88                 while (ret < 0) {
  89                         ret = try_to_remap((void *)auxval, vdso_size);
  90                         vdso_size += PAGE_SIZE;
  91                 }
  92
  93                 /* Glibc is likely to explode now - exit with raw syscall */
  94                 asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
  95         } else {
  96                 int status;
  97
  98                 if (waitpid(child, &status, 0) != child ||
  99                         !WIFEXITED(status)) {
 100                         printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");
 101                         return 1;
 102                 } else if (WEXITSTATUS(status) != 0) {
 103                         printf("[FAIL]\tChild failed with %d\n",
 104                                         WEXITSTATUS(status));
 105                         return 1;
 106                 }
 107                 printf("[OK]\n");
 108         }
 109
 110         return 0;
 111 }