1 // SPDX-License-Identifier: GPL-2.0+
2 //
3 // Copyright 2019, Michael Ellerman, IBM Corp.
4 //
5 // Test that allocating memory beyond the memory limit and then forking is
6 // handled correctly, ie. the child is able to access the mappings beyond the
7 // memory limit and the child's writes are not visible to the parent.
8 
9 #include <stdio.h>
10 #include <stdlib.h>
11 #include <sys/mman.h>
12 #include <sys/types.h>
13 #include <sys/wait.h>
14 #include <unistd.h>
15 
16 #include "utils.h"
17 
18 
19 #ifndef MAP_FIXED_NOREPLACE
20 #define MAP_FIXED_NOREPLACE	MAP_FIXED	// "Should be safe" above 512TB
21 #endif
22 
23 
test(void)24 static int test(void)
25 {
26 	int p2c[2], c2p[2], rc, status, c, *p;
27 	unsigned long page_size;
28 	pid_t pid;
29 
30 	page_size = sysconf(_SC_PAGESIZE);
31 	SKIP_IF(page_size != 65536);
32 
33 	// Create a mapping at 512TB to allocate an extended_id
34 	p = mmap((void *)(512ul << 40), page_size, PROT_READ | PROT_WRITE,
35 		MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE, -1, 0);
36 	if (p == MAP_FAILED) {
37 		perror("mmap");
38 		printf("Error: couldn't mmap(), confirm kernel has 4TB support?\n");
39 		return 1;
40 	}
41 
42 	printf("parent writing %p = 1\n", p);
43 	*p = 1;
44 
45 	FAIL_IF(pipe(p2c) == -1 || pipe(c2p) == -1);
46 
47 	pid = fork();
48 	if (pid == 0) {
49 		FAIL_IF(read(p2c[0], &c, 1) != 1);
50 
51 		pid = getpid();
52 		printf("child writing  %p = %d\n", p, pid);
53 		*p = pid;
54 
55 		FAIL_IF(write(c2p[1], &c, 1) != 1);
56 		FAIL_IF(read(p2c[0], &c, 1) != 1);
57 		exit(0);
58 	}
59 
60 	c = 0;
61 	FAIL_IF(write(p2c[1], &c, 1) != 1);
62 	FAIL_IF(read(c2p[0], &c, 1) != 1);
63 
64 	// Prevent compiler optimisation
65 	barrier();
66 
67 	rc = 0;
68 	printf("parent reading %p = %d\n", p, *p);
69 	if (*p != 1) {
70 		printf("Error: BUG! parent saw child's write! *p = %d\n", *p);
71 		rc = 1;
72 	}
73 
74 	FAIL_IF(write(p2c[1], &c, 1) != 1);
75 	FAIL_IF(waitpid(pid, &status, 0) == -1);
76 	FAIL_IF(!WIFEXITED(status) || WEXITSTATUS(status));
77 
78 	if (rc == 0)
79 		printf("success: test completed OK\n");
80 
81 	return rc;
82 }
83 
main(void)84 int main(void)
85 {
86 	return test_harness(test, "large_vm_fork_separation");
87 }
88