LXR linux/tools/testing/selftests/x86/test_mremap

   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
  33static 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
  65int 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}
 112