selftests/x86/test_mremap_vdso.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  * 32-bit test to check vDSO mremap.
0004  *
0005  * Copyright (c) 2016 Dmitry Safonov
0006  * Suggested-by: Andrew Lutomirski
0007  */
0008 /*
0009  * Can be built statically:
0010  * gcc -Os -Wall -static -m32 test_mremap_vdso.c
0011  */
0012 #define _GNU_SOURCE
0013 #include <stdio.h>
0014 #include <errno.h>
0015 #include <unistd.h>
0016 #include <string.h>
0017
0018 #include <sys/mman.h>
0019 #include <sys/auxv.h>
0020 #include <sys/syscall.h>
0021 #include <sys/wait.h>
0022
0023 #define PAGE_SIZE   4096
0024
0025 static int try_to_remap(void *vdso_addr, unsigned long size)
0026 {
0027     void *dest_addr, *new_addr;
0028
0029     /* Searching for memory location where to remap */
0030     dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
0031     if (dest_addr == MAP_FAILED) {
0032         printf("[WARN]\tmmap failed (%d): %m\n", errno);
0033         return 0;
0034     }
0035
0036     printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",
0037         vdso_addr, (unsigned long)vdso_addr + size,
0038         dest_addr, (unsigned long)dest_addr + size);
0039     fflush(stdout);
0040
0041     new_addr = mremap(vdso_addr, size, size,
0042             MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
0043     if ((unsigned long)new_addr == (unsigned long)-1) {
0044         munmap(dest_addr, size);
0045         if (errno == EINVAL) {
0046             printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");
0047             return -1; /* Retry with larger */
0048         }
0049         printf("[FAIL]\tmremap failed (%d): %m\n", errno);
0050         return 1;
0051     }
0052
0053     return 0;
0054
0055 }
0056
0057 int main(int argc, char **argv, char **envp)
0058 {
0059     pid_t child;
0060
0061     child = fork();
0062     if (child == -1) {
0063         printf("[WARN]\tfailed to fork (%d): %m\n", errno);
0064         return 1;
0065     }
0066
0067     if (child == 0) {
0068         unsigned long vdso_size = PAGE_SIZE;
0069         unsigned long auxval;
0070         int ret = -1;
0071
0072         auxval = getauxval(AT_SYSINFO_EHDR);
0073         printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);
0074         if (!auxval || auxval == -ENOENT) {
0075             printf("[WARN]\tgetauxval failed\n");
0076             return 0;
0077         }
0078
0079         /* Simpler than parsing ELF header */
0080         while (ret < 0) {
0081             ret = try_to_remap((void *)auxval, vdso_size);
0082             vdso_size += PAGE_SIZE;
0083         }
0084
0085 #ifdef __i386__
0086         /* Glibc is likely to explode now - exit with raw syscall */
0087         asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
0088 #else /* __x86_64__ */
0089         syscall(SYS_exit, ret);
0090 #endif
0091     } else {
0092         int status;
0093
0094         if (waitpid(child, &status, 0) != child ||
0095             !WIFEXITED(status)) {
0096             printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");
0097             return 1;
0098         } else if (WEXITSTATUS(status) != 0) {
0099             printf("[FAIL]\tChild failed with %d\n",
0100                     WEXITSTATUS(status));
0101             return 1;
0102         }
0103         printf("[OK]\n");
0104     }
0105
0106     return 0;
0107 }