1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (c) 2018 Dmitry Safonov, Arista Networks 4 * 5 * MAP_POPULATE | MAP_PRIVATE should COW VMA pages. 6 */ 7 8 #define _GNU_SOURCE 9 #include <errno.h> 10 #include <fcntl.h> 11 #include <sys/mman.h> 12 #include <sys/socket.h> 13 #include <sys/types.h> 14 #include <sys/wait.h> 15 #include <stdio.h> 16 #include <stdlib.h> 17 #include <string.h> 18 #include <unistd.h> 19 20 #ifndef MMAP_SZ 21 #define MMAP_SZ 4096 22 #endif 23 24 #define BUG_ON(condition, description) \ 25 do { \ 26 if (condition) { \ 27 fprintf(stderr, "[FAIL]\t%s:%d\t%s:%s\n", __func__, \ 28 __LINE__, (description), strerror(errno)); \ 29 exit(1); \ 30 } \ 31 } while (0) 32 33 static int parent_f(int sock, unsigned long *smap, int child) 34 { 35 int status, ret; 36 37 ret = read(sock, &status, sizeof(int)); 38 BUG_ON(ret <= 0, "read(sock)"); 39 40 *smap = 0x22222BAD; 41 ret = msync(smap, MMAP_SZ, MS_SYNC); 42 BUG_ON(ret, "msync()"); 43 44 ret = write(sock, &status, sizeof(int)); 45 BUG_ON(ret <= 0, "write(sock)"); 46 47 waitpid(child, &status, 0); 48 BUG_ON(!WIFEXITED(status), "child in unexpected state"); 49 50 return WEXITSTATUS(status); 51 } 52 53 static int child_f(int sock, unsigned long *smap, int fd) 54 { 55 int ret, buf = 0; 56 57 smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE, 58 MAP_PRIVATE | MAP_POPULATE, fd, 0); 59 BUG_ON(smap == MAP_FAILED, "mmap()"); 60 61 BUG_ON(*smap != 0xdeadbabe, "MAP_PRIVATE | MAP_POPULATE changed file"); 62 63 ret = write(sock, &buf, sizeof(int)); 64 BUG_ON(ret <= 0, "write(sock)"); 65 66 ret = read(sock, &buf, sizeof(int)); 67 BUG_ON(ret <= 0, "read(sock)"); 68 69 BUG_ON(*smap == 0x22222BAD, "MAP_POPULATE didn't COW private page"); 70 BUG_ON(*smap != 0xdeadbabe, "mapping was corrupted"); 71 72 return 0; 73 } 74 75 int main(int argc, char **argv) 76 { 77 int sock[2], child, ret; 78 FILE *ftmp; 79 unsigned long *smap; 80 81 ftmp = tmpfile(); 82 BUG_ON(ftmp == 0, "tmpfile()"); 83 84 ret = ftruncate(fileno(ftmp), MMAP_SZ); 85 BUG_ON(ret, "ftruncate()"); 86 87 smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE, 88 MAP_SHARED, fileno(ftmp), 0); 89 BUG_ON(smap == MAP_FAILED, "mmap()"); 90 91 *smap = 0xdeadbabe; 92 /* Probably unnecessary, but let it be. */ 93 ret = msync(smap, MMAP_SZ, MS_SYNC); 94 BUG_ON(ret, "msync()"); 95 96 ret = socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sock); 97 BUG_ON(ret, "socketpair()"); 98 99 child = fork(); 100 BUG_ON(child == -1, "fork()"); 101 102 if (child) { 103 ret = close(sock[0]); 104 BUG_ON(ret, "close()"); 105 106 return parent_f(sock[1], smap, child); 107 } 108 109 ret = close(sock[1]); 110 BUG_ON(ret, "close()"); 111 112 return child_f(sock[0], smap, fileno(ftmp)); 113 } 114