1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * 32-bit test to check vDSO mremap. 4 * 5 * Copyright (c) 2016 Dmitry Safonov 6 * Suggested-by: Andrew Lutomirski 7 */ 8 /* 9 * Can be built statically: 10 * gcc -Os -Wall -static -m32 test_mremap_vdso.c 11 */ 12 #define _GNU_SOURCE 13 #include <stdio.h> 14 #include <errno.h> 15 #include <unistd.h> 16 #include <string.h> 17 18 #include <sys/mman.h> 19 #include <sys/auxv.h> 20 #include <sys/syscall.h> 21 #include <sys/wait.h> 22 23 #define PAGE_SIZE 4096 24 25 static int try_to_remap(void *vdso_addr, unsigned long size) 26 { 27 void *dest_addr, *new_addr; 28 29 /* Searching for memory location where to remap */ 30 dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0); 31 if (dest_addr == MAP_FAILED) { 32 printf("[WARN]\tmmap failed (%d): %m\n", errno); 33 return 0; 34 } 35 36 printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n", 37 vdso_addr, (unsigned long)vdso_addr + size, 38 dest_addr, (unsigned long)dest_addr + size); 39 fflush(stdout); 40 41 new_addr = mremap(vdso_addr, size, size, 42 MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr); 43 if ((unsigned long)new_addr == (unsigned long)-1) { 44 munmap(dest_addr, size); 45 if (errno == EINVAL) { 46 printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n"); 47 return -1; /* Retry with larger */ 48 } 49 printf("[FAIL]\tmremap failed (%d): %m\n", errno); 50 return 1; 51 } 52 53 return 0; 54 55 } 56 57 int main(int argc, char **argv, char **envp) 58 { 59 pid_t child; 60 61 child = fork(); 62 if (child == -1) { 63 printf("[WARN]\tfailed to fork (%d): %m\n", errno); 64 return 1; 65 } 66 67 if (child == 0) { 68 unsigned long vdso_size = PAGE_SIZE; 69 unsigned long auxval; 70 int ret = -1; 71 72 auxval = getauxval(AT_SYSINFO_EHDR); 73 printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval); 74 if (!auxval || auxval == -ENOENT) { 75 printf("[WARN]\tgetauxval failed\n"); 76 return 0; 77 } 78 79 /* Simpler than parsing ELF header */ 80 while (ret < 0) { 81 ret = try_to_remap((void *)auxval, vdso_size); 82 vdso_size += PAGE_SIZE; 83 } 84 85 #ifdef __i386__ 86 /* Glibc is likely to explode now - exit with raw syscall */ 87 asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret)); 88 #else /* __x86_64__ */ 89 syscall(SYS_exit, ret); 90 #endif 91 } else { 92 int status; 93 94 if (waitpid(child, &status, 0) != child || 95 !WIFEXITED(status)) { 96 printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n"); 97 return 1; 98 } else if (WEXITSTATUS(status) != 0) { 99 printf("[FAIL]\tChild failed with %d\n", 100 WEXITSTATUS(status)); 101 return 1; 102 } 103 printf("[OK]\n"); 104 } 105 106 return 0; 107 } 108