tools/testing/selftests/syscall_user_dispatch/sud_test.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (c) 2020 Collabora Ltd.
   4  *
   5  * Test code for syscall user dispatch
   6  */
   7
   8 #define _GNU_SOURCE
   9 #include <sys/prctl.h>
  10 #include <sys/sysinfo.h>
  11 #include <sys/syscall.h>
  12 #include <signal.h>
  13
  14 #include <asm/unistd.h>
  15 #include "../kselftest_harness.h"
  16
  17 #ifndef PR_SET_SYSCALL_USER_DISPATCH
  18 # define PR_SET_SYSCALL_USER_DISPATCH   59
  19 # define PR_SYS_DISPATCH_OFF    0
  20 # define PR_SYS_DISPATCH_ON     1
  21 # define SYSCALL_DISPATCH_FILTER_ALLOW  0
  22 # define SYSCALL_DISPATCH_FILTER_BLOCK  1
  23 #endif
  24
  25 #ifndef SYS_USER_DISPATCH
  26 # define SYS_USER_DISPATCH      2
  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 #define SYSCALL_DISPATCH_ON(x) ((x) = SYSCALL_DISPATCH_FILTER_BLOCK)
  36 #define SYSCALL_DISPATCH_OFF(x) ((x) = SYSCALL_DISPATCH_FILTER_ALLOW)
  37
  38 /* Test Summary:
  39  *
  40  * - dispatch_trigger_sigsys: Verify if PR_SET_SYSCALL_USER_DISPATCH is
  41  *   able to trigger SIGSYS on a syscall.
  42  *
  43  * - bad_selector: Test that a bad selector value triggers SIGSYS with
  44  *   si_errno EINVAL.
  45  *
  46  * - bad_prctl_param: Test that the API correctly rejects invalid
  47  *   parameters on prctl
  48  *
  49  * - dispatch_and_return: Test that a syscall is selectively dispatched
  50  *   to userspace depending on the value of selector.
  51  *
  52  * - disable_dispatch: Test that the PR_SYS_DISPATCH_OFF correctly
  53  *   disables the dispatcher
  54  *
  55  * - direct_dispatch_range: Test that a syscall within the allowed range
  56  *   can bypass the dispatcher.
  57  */
  58
  59 TEST_SIGNAL(dispatch_trigger_sigsys, SIGSYS)
  60 {
  61         char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
  62         struct sysinfo info;
  63         int ret;
  64
  65         ret = sysinfo(&info);
  66         ASSERT_EQ(0, ret);
  67
  68         ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &sel);
  69         ASSERT_EQ(0, ret) {
  70                 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
  71         }
  72
  73         SYSCALL_DISPATCH_ON(sel);
  74
  75         sysinfo(&info);
  76
  77         EXPECT_FALSE(true) {
  78                 TH_LOG("Unreachable!");
  79         }
  80 }
  81
  82 TEST(bad_prctl_param)
  83 {
  84         char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
  85         int op;
  86
  87         /* Invalid op */
  88         op = -1;
  89         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0, 0, &sel);
  90         ASSERT_EQ(EINVAL, errno);
  91
  92         /* PR_SYS_DISPATCH_OFF */
  93         op = PR_SYS_DISPATCH_OFF;
  94
  95         /* offset != 0 */
  96         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, 0);
  97         EXPECT_EQ(EINVAL, errno);
  98
  99         /* len != 0 */
 100         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0xff, 0);
 101         EXPECT_EQ(EINVAL, errno);
 102
 103         /* sel != NULL */
 104         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, &sel);
 105         EXPECT_EQ(EINVAL, errno);
 106
 107         /* Valid parameter */
 108         errno = 0;
 109         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x0, 0x0);
 110         EXPECT_EQ(0, errno);
 111
 112         /* PR_SYS_DISPATCH_ON */
 113         op = PR_SYS_DISPATCH_ON;
 114
 115         /* Dispatcher region is bad (offset > 0 && len == 0) */
 116         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x1, 0x0, &sel);
 117         EXPECT_EQ(EINVAL, errno);
 118         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, -1L, 0x0, &sel);
 119         EXPECT_EQ(EINVAL, errno);
 120
 121         /* Invalid selector */
 122         prctl(PR_SET_SYSCALL_USER_DISPATCH, op, 0x0, 0x1, (void *) -1);
 123         ASSERT_EQ(EFAULT, errno);
 124
 125         /*
 126          * Dispatcher range overflows unsigned long
 127          */
 128         prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 1, -1L, &sel);
 129         ASSERT_EQ(EINVAL, errno) {
 130                 TH_LOG("Should reject bad syscall range");
 131         }
 132
 133         /*
 134          * Allowed range overflows usigned long
 135          */
 136         prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, -1L, 0x1, &sel);
 137         ASSERT_EQ(EINVAL, errno) {
 138                 TH_LOG("Should reject bad syscall range");
 139         }
 140 }
 141
 142 /*
 143  * Use global selector for handle_sigsys tests, to avoid passing
 144  * selector to signal handler
 145  */
 146 char glob_sel;
 147 int nr_syscalls_emulated;
 148 int si_code;
 149 int si_errno;
 150
 151 static void handle_sigsys(int sig, siginfo_t *info, void *ucontext)
 152 {
 153         si_code = info->si_code;
 154         si_errno = info->si_errno;
 155
 156         if (info->si_syscall == MAGIC_SYSCALL_1)
 157                 nr_syscalls_emulated++;
 158
 159         /* In preparation for sigreturn. */
 160         SYSCALL_DISPATCH_OFF(glob_sel);
 161
 162         /*
 163          * The tests for argument handling assume that `syscall(x) == x`. This
 164          * is a NOP on x86 because the syscall number is passed in %rax, which
 165          * happens to also be the function ABI return register.  Other
 166          * architectures may need to swizzle the arguments around.
 167          */
 168 #if defined(__riscv)
 169 /* REG_A7 is not defined in libc headers */
 170 # define REG_A7 (REG_A0 + 7)
 171
 172         ((ucontext_t *)ucontext)->uc_mcontext.__gregs[REG_A0] =
 173                         ((ucontext_t *)ucontext)->uc_mcontext.__gregs[REG_A7];
 174 #endif
 175 }
 176
 177 TEST(dispatch_and_return)
 178 {
 179         long ret;
 180         struct sigaction act;
 181         sigset_t mask;
 182
 183         glob_sel = 0;
 184         nr_syscalls_emulated = 0;
 185         si_code = 0;
 186         si_errno = 0;
 187
 188         memset(&act, 0, sizeof(act));
 189         sigemptyset(&mask);
 190
 191         act.sa_sigaction = handle_sigsys;
 192         act.sa_flags = SA_SIGINFO;
 193         act.sa_mask = mask;
 194
 195         ret = sigaction(SIGSYS, &act, NULL);
 196         ASSERT_EQ(0, ret);
 197
 198         /* Make sure selector is good prior to prctl. */
 199         SYSCALL_DISPATCH_OFF(glob_sel);
 200
 201         ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &glob_sel);
 202         ASSERT_EQ(0, ret) {
 203                 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
 204         }
 205
 206         /* MAGIC_SYSCALL_1 doesn't exist. */
 207         SYSCALL_DISPATCH_OFF(glob_sel);
 208         ret = syscall(MAGIC_SYSCALL_1);
 209         EXPECT_EQ(-1, ret) {
 210                 TH_LOG("Dispatch triggered unexpectedly");
 211         }
 212
 213         /* MAGIC_SYSCALL_1 should be emulated. */
 214         nr_syscalls_emulated = 0;
 215         SYSCALL_DISPATCH_ON(glob_sel);
 216
 217         ret = syscall(MAGIC_SYSCALL_1);
 218         EXPECT_EQ(MAGIC_SYSCALL_1, ret) {
 219                 TH_LOG("Failed to intercept syscall");
 220         }
 221         EXPECT_EQ(1, nr_syscalls_emulated) {
 222                 TH_LOG("Failed to emulate syscall");
 223         }
 224         ASSERT_EQ(SYS_USER_DISPATCH, si_code) {
 225                 TH_LOG("Bad si_code in SIGSYS");
 226         }
 227         ASSERT_EQ(0, si_errno) {
 228                 TH_LOG("Bad si_errno in SIGSYS");
 229         }
 230 }
 231
 232 TEST_SIGNAL(bad_selector, SIGSYS)
 233 {
 234         long ret;
 235         struct sigaction act;
 236         sigset_t mask;
 237         struct sysinfo info;
 238
 239         glob_sel = SYSCALL_DISPATCH_FILTER_ALLOW;
 240         nr_syscalls_emulated = 0;
 241         si_code = 0;
 242         si_errno = 0;
 243
 244         memset(&act, 0, sizeof(act));
 245         sigemptyset(&mask);
 246
 247         act.sa_sigaction = handle_sigsys;
 248         act.sa_flags = SA_SIGINFO;
 249         act.sa_mask = mask;
 250
 251         ret = sigaction(SIGSYS, &act, NULL);
 252         ASSERT_EQ(0, ret);
 253
 254         /* Make sure selector is good prior to prctl. */
 255         SYSCALL_DISPATCH_OFF(glob_sel);
 256
 257         ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &glob_sel);
 258         ASSERT_EQ(0, ret) {
 259                 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
 260         }
 261
 262         glob_sel = -1;
 263
 264         sysinfo(&info);
 265
 266         /* Even though it is ready to catch SIGSYS, the signal is
 267          * supposed to be uncatchable.
 268          */
 269
 270         EXPECT_FALSE(true) {
 271                 TH_LOG("Unreachable!");
 272         }
 273 }
 274
 275 TEST(disable_dispatch)
 276 {
 277         int ret;
 278         struct sysinfo info;
 279         char sel = 0;
 280
 281         ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &sel);
 282         ASSERT_EQ(0, ret) {
 283                 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
 284         }
 285
 286         /* MAGIC_SYSCALL_1 doesn't exist. */
 287         SYSCALL_DISPATCH_OFF(glob_sel);
 288
 289         ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_OFF, 0, 0, 0);
 290         EXPECT_EQ(0, ret) {
 291                 TH_LOG("Failed to unset syscall user dispatch");
 292         }
 293
 294         /* Shouldn't have any effect... */
 295         SYSCALL_DISPATCH_ON(glob_sel);
 296
 297         ret = syscall(__NR_sysinfo, &info);
 298         EXPECT_EQ(0, ret) {
 299                 TH_LOG("Dispatch triggered unexpectedly");
 300         }
 301 }
 302
 303 TEST(direct_dispatch_range)
 304 {
 305         int ret = 0;
 306         struct sysinfo info;
 307         char sel = SYSCALL_DISPATCH_FILTER_ALLOW;
 308
 309         /*
 310          * Instead of calculating libc addresses; allow the entire
 311          * memory map and lock the selector.
 312          */
 313         ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, -1L, &sel);
 314         ASSERT_EQ(0, ret) {
 315                 TH_LOG("Kernel does not support CONFIG_SYSCALL_USER_DISPATCH");
 316         }
 317
 318         SYSCALL_DISPATCH_ON(sel);
 319
 320         ret = sysinfo(&info);
 321         ASSERT_EQ(0, ret) {
 322                 TH_LOG("Dispatch triggered unexpectedly");
 323         }
 324 }
 325
 326 TEST_HARNESS_MAIN