1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (c) 2020 Collabora Ltd.
4 *
5 * Benchmark and test syscall user dispatch
6 */
7
8 #define _GNU_SOURCE
9 #include <stdio.h>
10 #include <string.h>
11 #include <stdlib.h>
12 #include <signal.h>
13 #include <errno.h>
14 #include <time.h>
15 #include <sys/time.h>
16 #include <unistd.h>
17 #include <sys/sysinfo.h>
18 #include <sys/prctl.h>
19 #include <sys/syscall.h>
20
21 #ifndef PR_SET_SYSCALL_USER_DISPATCH
22 # define PR_SET_SYSCALL_USER_DISPATCH 59
23 # define PR_SYS_DISPATCH_OFF 0
24 # define PR_SYS_DISPATCH_ON 1
25 # define SYSCALL_DISPATCH_FILTER_ALLOW 0
26 # define SYSCALL_DISPATCH_FILTER_BLOCK 1
27 #endif
28
29 #ifdef __NR_syscalls
30 # define MAGIC_SYSCALL_1 (__NR_syscalls + 1) /* Bad Linux syscall number */
31 #else
32 # define MAGIC_SYSCALL_1 (0xff00) /* Bad Linux syscall number */
33 #endif
34
35 /*
36 * To test returning from a sigsys with selector blocked, the test
37 * requires some per-architecture support (i.e. knowledge about the
38 * signal trampoline address). On i386, we know it is on the vdso, and
39 * a small trampoline is open-coded for x86_64. Other architectures
40 * that have a trampoline in the vdso will support TEST_BLOCKED_RETURN
41 * out of the box, but don't enable them until they support syscall user
42 * dispatch.
43 */
44 #if defined(__x86_64__) || defined(__i386__)
45 #define TEST_BLOCKED_RETURN
46 #endif
47
48 #ifdef __x86_64__
49 void* (syscall_dispatcher_start)(void);
50 void* (syscall_dispatcher_end)(void);
51 #else
52 unsigned long syscall_dispatcher_start = 0;
53 unsigned long syscall_dispatcher_end = 0;
54 #endif
55
56 unsigned long trapped_call_count = 0;
57 unsigned long native_call_count = 0;
58
59 char selector;
60 #define SYSCALL_BLOCK (selector = SYSCALL_DISPATCH_FILTER_BLOCK)
61 #define SYSCALL_UNBLOCK (selector = SYSCALL_DISPATCH_FILTER_ALLOW)
62
63 #define CALIBRATION_STEP 100000
64 #define CALIBRATE_TO_SECS 5
65 int factor;
66
one_sysinfo_step(void)67 static double one_sysinfo_step(void)
68 {
69 struct timespec t1, t2;
70 int i;
71 struct sysinfo info;
72
73 clock_gettime(CLOCK_MONOTONIC, &t1);
74 for (i = 0; i < CALIBRATION_STEP; i++)
75 sysinfo(&info);
76 clock_gettime(CLOCK_MONOTONIC, &t2);
77 return (t2.tv_sec - t1.tv_sec) + 1.0e-9 * (t2.tv_nsec - t1.tv_nsec);
78 }
79
calibrate_set(void)80 static void calibrate_set(void)
81 {
82 double elapsed = 0;
83
84 printf("Calibrating test set to last ~%d seconds...\n", CALIBRATE_TO_SECS);
85
86 while (elapsed < 1) {
87 elapsed += one_sysinfo_step();
88 factor += CALIBRATE_TO_SECS;
89 }
90
91 printf("test iterations = %d\n", CALIBRATION_STEP * factor);
92 }
93
perf_syscall(void)94 static double perf_syscall(void)
95 {
96 unsigned int i;
97 double partial = 0;
98
99 for (i = 0; i < factor; ++i)
100 partial += one_sysinfo_step()/(CALIBRATION_STEP*factor);
101 return partial;
102 }
103
handle_sigsys(int sig,siginfo_t * info,void * ucontext)104 static void handle_sigsys(int sig, siginfo_t *info, void *ucontext)
105 {
106 char buf[1024];
107 int len;
108
109 SYSCALL_UNBLOCK;
110
111 /* printf and friends are not signal-safe. */
112 len = snprintf(buf, 1024, "Caught sys_%x\n", info->si_syscall);
113 write(1, buf, len);
114
115 if (info->si_syscall == MAGIC_SYSCALL_1)
116 trapped_call_count++;
117 else
118 native_call_count++;
119
120 #ifdef TEST_BLOCKED_RETURN
121 SYSCALL_BLOCK;
122 #endif
123
124 #ifdef __x86_64__
125 __asm__ volatile("movq $0xf, %rax");
126 __asm__ volatile("leaveq");
127 __asm__ volatile("add $0x8, %rsp");
128 __asm__ volatile("syscall_dispatcher_start:");
129 __asm__ volatile("syscall");
130 __asm__ volatile("nop"); /* Landing pad within dispatcher area */
131 __asm__ volatile("syscall_dispatcher_end:");
132 #endif
133
134 }
135
main(void)136 int main(void)
137 {
138 struct sigaction act;
139 double time1, time2;
140 int ret;
141 sigset_t mask;
142
143 memset(&act, 0, sizeof(act));
144 sigemptyset(&mask);
145
146 act.sa_sigaction = handle_sigsys;
147 act.sa_flags = SA_SIGINFO;
148 act.sa_mask = mask;
149
150 calibrate_set();
151
152 time1 = perf_syscall();
153 printf("Avg syscall time %.0lfns.\n", time1 * 1.0e9);
154
155 ret = sigaction(SIGSYS, &act, NULL);
156 if (ret) {
157 perror("Error sigaction:");
158 exit(-1);
159 }
160
161 fprintf(stderr, "Enabling syscall trapping.\n");
162
163 if (prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON,
164 syscall_dispatcher_start,
165 (syscall_dispatcher_end - syscall_dispatcher_start + 1),
166 &selector)) {
167 perror("prctl failed\n");
168 exit(-1);
169 }
170
171 SYSCALL_BLOCK;
172 syscall(MAGIC_SYSCALL_1);
173
174 #ifdef TEST_BLOCKED_RETURN
175 if (selector == SYSCALL_DISPATCH_FILTER_ALLOW) {
176 fprintf(stderr, "Failed to return with selector blocked.\n");
177 exit(-1);
178 }
179 #endif
180
181 SYSCALL_UNBLOCK;
182
183 if (!trapped_call_count) {
184 fprintf(stderr, "syscall trapping does not work.\n");
185 exit(-1);
186 }
187
188 time2 = perf_syscall();
189
190 if (native_call_count) {
191 perror("syscall trapping intercepted more syscalls than expected\n");
192 exit(-1);
193 }
194
195 printf("trapped_call_count %lu, native_call_count %lu.\n",
196 trapped_call_count, native_call_count);
197 printf("Avg syscall time %.0lfns.\n", time2 * 1.0e9);
198 printf("Interception overhead: %.1lf%% (+%.0lfns).\n",
199 100.0 * (time2 / time1 - 1.0), 1.0e9 * (time2 - time1));
200 return 0;
201
202 }
203