tools/testing/selftests/syscall_user_dispatch/sud_benchmark.c

   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
  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
  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
  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
 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
 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 }