1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * Test that a syscall does not get restarted twice, handled by trap_norestart()
4  *
5  * Based on Al's description, and a test for the bug fixed in this commit:
6  *
7  * commit 9a81c16b527528ad307843be5571111aa8d35a80
8  * Author: Al Viro <viro@zeniv.linux.org.uk>
9  * Date:   Mon Sep 20 21:48:57 2010 +0100
10  *
11  *  powerpc: fix double syscall restarts
12  *
13  *  Make sigreturn zero regs->trap, make do_signal() do the same on all
14  *  paths.  As it is, signal interrupting e.g. read() from fd 512 (==
15  *  ERESTARTSYS) with another signal getting unblocked when the first
16  *  handler finishes will lead to restart one insn earlier than it ought
17  *  to.  Same for multiple signals with in-kernel handlers interrupting
18  *  that sucker at the same time.  Same for multiple signals of any kind
19  *  interrupting that sucker on 64bit...
20  */
21 #define _GNU_SOURCE
22 #include <sys/types.h>
23 #include <sys/wait.h>
24 #include <sys/syscall.h>
25 #include <unistd.h>
26 #include <signal.h>
27 #include <errno.h>
28 #include <stdlib.h>
29 #include <stdio.h>
30 #include <string.h>
31 
32 #include "utils.h"
33 
34 static void SIGUSR1_handler(int sig)
35 {
36 	kill(getpid(), SIGUSR2);
37 	/*
38 	 * SIGUSR2 is blocked until the handler exits, at which point it will
39 	 * be raised again and think there is a restart to be done because the
40 	 * pending restarted syscall has 512 (ERESTARTSYS) in r3. The second
41 	 * restart will retreat NIP another 4 bytes to fail case branch.
42 	 */
43 }
44 
45 static void SIGUSR2_handler(int sig)
46 {
47 }
48 
49 static ssize_t raw_read(int fd, void *buf, size_t count)
50 {
51 	register long nr asm("r0") = __NR_read;
52 	register long _fd asm("r3") = fd;
53 	register void *_buf asm("r4") = buf;
54 	register size_t _count asm("r5") = count;
55 
56 	asm volatile(
57 "		b	0f		\n"
58 "		b	1f		\n"
59 "	0:	sc	0		\n"
60 "		bns	2f		\n"
61 "		neg	%0,%0		\n"
62 "		b	2f		\n"
63 "	1:				\n"
64 "		li	%0,%4		\n"
65 "	2:				\n"
66 		: "+r"(_fd), "+r"(nr), "+r"(_buf), "+r"(_count)
67 		: "i"(-ENOANO)
68 		: "memory", "r6", "r7", "r8", "r9", "r10", "r11", "r12", "ctr", "cr0");
69 
70 	if (_fd < 0) {
71 		errno = -_fd;
72 		_fd = -1;
73 	}
74 
75 	return _fd;
76 }
77 
78 #define DATA "test 123"
79 #define DLEN (strlen(DATA)+1)
80 
81 int test_restart(void)
82 {
83 	int pipefd[2];
84 	pid_t pid;
85 	char buf[512];
86 
87 	if (pipe(pipefd) == -1) {
88 		perror("pipe");
89 		exit(EXIT_FAILURE);
90 	}
91 
92 	pid = fork();
93 	if (pid == -1) {
94 		perror("fork");
95 		exit(EXIT_FAILURE);
96 	}
97 
98 	if (pid == 0) { /* Child reads from pipe */
99 		struct sigaction act;
100 		int fd;
101 
102 		memset(&act, 0, sizeof(act));
103 		sigaddset(&act.sa_mask, SIGUSR2);
104 		act.sa_handler = SIGUSR1_handler;
105 		act.sa_flags = SA_RESTART;
106 		if (sigaction(SIGUSR1, &act, NULL) == -1) {
107 			perror("sigaction");
108 			exit(EXIT_FAILURE);
109 		}
110 
111 		memset(&act, 0, sizeof(act));
112 		act.sa_handler = SIGUSR2_handler;
113 		act.sa_flags = SA_RESTART;
114 		if (sigaction(SIGUSR2, &act, NULL) == -1) {
115 			perror("sigaction");
116 			exit(EXIT_FAILURE);
117 		}
118 
119 		/* Let's get ERESTARTSYS into r3 */
120 		while ((fd = dup(pipefd[0])) != 512) {
121 			if (fd == -1) {
122 				perror("dup");
123 				exit(EXIT_FAILURE);
124 			}
125 		}
126 
127 		if (raw_read(fd, buf, 512) == -1) {
128 			if (errno == ENOANO) {
129 				fprintf(stderr, "Double restart moved restart before sc instruction.\n");
130 				_exit(EXIT_FAILURE);
131 			}
132 			perror("read");
133 			exit(EXIT_FAILURE);
134 		}
135 
136 		if (strncmp(buf, DATA, DLEN)) {
137 			fprintf(stderr, "bad test string %s\n", buf);
138 			exit(EXIT_FAILURE);
139 		}
140 
141 		return 0;
142 
143 	} else {
144 		int wstatus;
145 
146 		usleep(100000);		/* Hack to get reader waiting */
147 		kill(pid, SIGUSR1);
148 		usleep(100000);
149 		if (write(pipefd[1], DATA, DLEN) != DLEN) {
150 			perror("write");
151 			exit(EXIT_FAILURE);
152 		}
153 		close(pipefd[0]);
154 		close(pipefd[1]);
155 		if (wait(&wstatus) == -1) {
156 			perror("wait");
157 			exit(EXIT_FAILURE);
158 		}
159 		if (!WIFEXITED(wstatus)) {
160 			fprintf(stderr, "child exited abnormally\n");
161 			exit(EXIT_FAILURE);
162 		}
163 
164 		FAIL_IF(WEXITSTATUS(wstatus) != EXIT_SUCCESS);
165 
166 		return 0;
167 	}
168 }
169 
170 int main(void)
171 {
172 	test_harness_set_timeout(10);
173 	return test_harness(test_restart, "sig sys restart");
174 }
175