// SPDX-License-Identifier: GPL-2.0-only
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/*
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* 32-bit test to check vDSO mremap.
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*
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* Copyright (c) 2016 Dmitry Safonov
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* Suggested-by: Andrew Lutomirski
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*/
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/*
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* Can be built statically:
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* gcc -Os -Wall -static -m32 test_mremap_vdso.c
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*/
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#define _GNU_SOURCE
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#include <stdio.h>
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#include <errno.h>
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#include <unistd.h>
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#include <string.h>
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#include <sys/mman.h>
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#include <sys/auxv.h>
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#include <sys/syscall.h>
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#include <sys/wait.h>
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#define PAGE_SIZE 4096
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static int try_to_remap(void *vdso_addr, unsigned long size)
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{
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void *dest_addr, *new_addr;
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/* Searching for memory location where to remap */
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dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
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if (dest_addr == MAP_FAILED) {
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printf("[WARN]\tmmap failed (%d): %m\n", errno);
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return 0;
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}
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printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",
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vdso_addr, (unsigned long)vdso_addr + size,
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dest_addr, (unsigned long)dest_addr + size);
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fflush(stdout);
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new_addr = mremap(vdso_addr, size, size,
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MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
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if ((unsigned long)new_addr == (unsigned long)-1) {
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munmap(dest_addr, size);
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if (errno == EINVAL) {
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printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");
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return -1; /* Retry with larger */
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}
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printf("[FAIL]\tmremap failed (%d): %m\n", errno);
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return 1;
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}
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return 0;
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}
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int main(int argc, char **argv, char **envp)
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{
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pid_t child;
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child = fork();
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if (child == -1) {
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printf("[WARN]\tfailed to fork (%d): %m\n", errno);
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return 1;
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}
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if (child == 0) {
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unsigned long vdso_size = PAGE_SIZE;
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unsigned long auxval;
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int ret = -1;
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auxval = getauxval(AT_SYSINFO_EHDR);
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printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);
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if (!auxval || auxval == -ENOENT) {
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printf("[WARN]\tgetauxval failed\n");
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return 0;
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}
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/* Simpler than parsing ELF header */
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while (ret < 0) {
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ret = try_to_remap((void *)auxval, vdso_size);
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vdso_size += PAGE_SIZE;
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}
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#ifdef __i386__
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/* Glibc is likely to explode now - exit with raw syscall */
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asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
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#else /* __x86_64__ */
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syscall(SYS_exit, ret);
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#endif
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} else {
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int status;
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if (waitpid(child, &status, 0) != child ||
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!WIFEXITED(status)) {
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printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");
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return 1;
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} else if (WEXITSTATUS(status) != 0) {
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printf("[FAIL]\tChild failed with %d\n",
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WEXITSTATUS(status));
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return 1;
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}
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printf("[OK]\n");
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}
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return 0;
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}
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