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| 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 | +} |
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