sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.cc

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // Note: any code in this file MUST be async-signal safe.
   6
   7 #include "sandbox/linux/seccomp-bpf-helpers/sigsys_handlers.h"
   8
   9 #include <sys/syscall.h>
  10 #include <unistd.h>
  11
  12 #include "base/logging.h"
  13 #include "base/posix/eintr_wrapper.h"
  14 #include "build/build_config.h"
  15 #include "sandbox/linux/bpf_dsl/bpf_dsl.h"
  16 #include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
  17 #include "sandbox/linux/seccomp-bpf/syscall.h"
  18 #include "sandbox/linux/services/syscall_wrappers.h"
  19 #include "sandbox/linux/system_headers/linux_syscalls.h"
  20
  21 #if defined(__mips__)
  22 // __NR_Linux, is defined in <asm/unistd.h>.
  23 #include <asm/unistd.h>
  24 #endif
  25
  26 #define SECCOMP_MESSAGE_COMMON_CONTENT "seccomp-bpf failure"
  27 #define SECCOMP_MESSAGE_CLONE_CONTENT "clone() failure"
  28 #define SECCOMP_MESSAGE_PRCTL_CONTENT "prctl() failure"
  29 #define SECCOMP_MESSAGE_IOCTL_CONTENT "ioctl() failure"
  30 #define SECCOMP_MESSAGE_KILL_CONTENT "(tg)kill() failure"
  31 #define SECCOMP_MESSAGE_FUTEX_CONTENT "futex() failure"
  32
  33 namespace {
  34
  35 inline bool IsArchitectureX86_64() {
  36 #if defined(__x86_64__)
  37   return true;
  38 #else
  39   return false;
  40 #endif
  41 }
  42
  43 // Write |error_message| to stderr. Similar to RawLog(), but a bit more careful
  44 // about async-signal safety. |size| is the size to write and should typically
  45 // not include a terminating \0.
  46 void WriteToStdErr(const char* error_message, size_t size) {
  47   while (size > 0) {
  48     // TODO(jln): query the current policy to check if send() is available and
  49     // use it to perform a non-blocking write.
  50     const int ret = HANDLE_EINTR(write(STDERR_FILENO, error_message, size));
  51     // We can't handle any type of error here.
  52     if (ret <= 0 || static_cast<size_t>(ret) > size) break;
  53     size -= ret;
  54     error_message += ret;
  55   }
  56 }
  57
  58 // Invalid syscall values are truncated to zero.
  59 // On architectures where base value is zero (Intel and Arm),
  60 // syscall number is the same as offset from base.
  61 // This function returns values between 0 and 1023 on all architectures.
  62 // On architectures where base value is different than zero (currently only
  63 // Mips), we are truncating valid syscall values to offset from base.
  64 uint32_t SyscallNumberToOffsetFromBase(uint32_t sysno) {
  65 #if defined(__mips__)
  66   // On MIPS syscall numbers are in different range than on x86 and ARM.
  67   // Valid MIPS O32 ABI syscall __NR_syscall will be truncated to zero for
  68   // simplicity.
  69   sysno = sysno - __NR_Linux;
  70 #endif
  71
  72   if (sysno >= 1024)
  73     sysno = 0;
  74
  75   return sysno;
  76 }
  77
  78 // Print a seccomp-bpf failure to handle |sysno| to stderr in an
  79 // async-signal safe way.
  80 void PrintSyscallError(uint32_t sysno) {
  81   if (sysno >= 1024)
  82     sysno = 0;
  83   // TODO(markus): replace with async-signal safe snprintf when available.
  84   const size_t kNumDigits = 4;
  85   char sysno_base10[kNumDigits];
  86   uint32_t rem = sysno;
  87   uint32_t mod = 0;
  88   for (int i = kNumDigits - 1; i >= 0; i--) {
  89     mod = rem % 10;
  90     rem /= 10;
  91     sysno_base10[i] = '0' + mod;
  92   }
  93 #if defined(__mips__) && (_MIPS_SIM == _MIPS_SIM_ABI32)
  94   static const char kSeccompErrorPrefix[] = __FILE__
  95       ":**CRASHING**:" SECCOMP_MESSAGE_COMMON_CONTENT " in syscall 4000 + ";
  96 #else
  97   static const char kSeccompErrorPrefix[] =
  98       __FILE__":**CRASHING**:" SECCOMP_MESSAGE_COMMON_CONTENT " in syscall ";
  99 #endif
 100   static const char kSeccompErrorPostfix[] = "\n";
 101   WriteToStdErr(kSeccompErrorPrefix, sizeof(kSeccompErrorPrefix) - 1);
 102   WriteToStdErr(sysno_base10, sizeof(sysno_base10));
 103   WriteToStdErr(kSeccompErrorPostfix, sizeof(kSeccompErrorPostfix) - 1);
 104 }
 105
 106 }  // namespace.
 107
 108 namespace sandbox {
 109
 110 intptr_t CrashSIGSYS_Handler(const struct arch_seccomp_data& args, void* aux) {
 111   uint32_t syscall = SyscallNumberToOffsetFromBase(args.nr);
 112
 113   PrintSyscallError(syscall);
 114
 115   // Encode 8-bits of the 1st two arguments too, so we can discern which socket
 116   // type, which fcntl, ... etc., without being likely to hit a mapped
 117   // address.
 118   // Do not encode more bits here without thinking about increasing the
 119   // likelihood of collision with mapped pages.
 120   syscall |= ((args.args[0] & 0xffUL) << 12);
 121   syscall |= ((args.args[1] & 0xffUL) << 20);
 122   // Purposefully dereference the syscall as an address so it'll show up very
 123   // clearly and easily in crash dumps.
 124   volatile char* addr = reinterpret_cast<volatile char*>(syscall);
 125   *addr = '\0';
 126   // In case we hit a mapped address, hit the null page with just the syscall,
 127   // for paranoia.
 128   syscall &= 0xfffUL;
 129   addr = reinterpret_cast<volatile char*>(syscall);
 130   *addr = '\0';
 131   for (;;)
 132     _exit(1);
 133 }
 134
 135 // TODO(jln): refactor the reporting functions.
 136
 137 intptr_t SIGSYSCloneFailure(const struct arch_seccomp_data& args, void* aux) {
 138   static const char kSeccompCloneError[] =
 139       __FILE__":**CRASHING**:" SECCOMP_MESSAGE_CLONE_CONTENT "\n";
 140   WriteToStdErr(kSeccompCloneError, sizeof(kSeccompCloneError) - 1);
 141   // "flags" is the first argument in the kernel's clone().
 142   // Mark as volatile to be able to find the value on the stack in a minidump.
 143   volatile uint64_t clone_flags = args.args[0];
 144   volatile char* addr;
 145   if (IsArchitectureX86_64()) {
 146     addr = reinterpret_cast<volatile char*>(clone_flags & 0xFFFFFF);
 147     *addr = '\0';
 148   }
 149   // Hit the NULL page if this fails to fault.
 150   addr = reinterpret_cast<volatile char*>(clone_flags & 0xFFF);
 151   *addr = '\0';
 152   for (;;)
 153     _exit(1);
 154 }
 155
 156 intptr_t SIGSYSPrctlFailure(const struct arch_seccomp_data& args,
 157                             void* /* aux */) {
 158   static const char kSeccompPrctlError[] =
 159       __FILE__":**CRASHING**:" SECCOMP_MESSAGE_PRCTL_CONTENT "\n";
 160   WriteToStdErr(kSeccompPrctlError, sizeof(kSeccompPrctlError) - 1);
 161   // Mark as volatile to be able to find the value on the stack in a minidump.
 162   volatile uint64_t option = args.args[0];
 163   volatile char* addr =
 164       reinterpret_cast<volatile char*>(option & 0xFFF);
 165   *addr = '\0';
 166   for (;;)
 167     _exit(1);
 168 }
 169
 170 intptr_t SIGSYSIoctlFailure(const struct arch_seccomp_data& args,
 171                             void* /* aux */) {
 172   static const char kSeccompIoctlError[] =
 173       __FILE__":**CRASHING**:" SECCOMP_MESSAGE_IOCTL_CONTENT "\n";
 174   WriteToStdErr(kSeccompIoctlError, sizeof(kSeccompIoctlError) - 1);
 175   // Make "request" volatile so that we can see it on the stack in a minidump.
 176   volatile uint64_t request = args.args[1];
 177   volatile char* addr = reinterpret_cast<volatile char*>(request & 0xFFFF);
 178   *addr = '\0';
 179   // Hit the NULL page if this fails.
 180   addr = reinterpret_cast<volatile char*>(request & 0xFFF);
 181   *addr = '\0';
 182   for (;;)
 183     _exit(1);
 184 }
 185
 186 intptr_t SIGSYSKillFailure(const struct arch_seccomp_data& args,
 187                            void* /* aux */) {
 188    static const char kSeccompKillError[] =
 189       __FILE__":**CRASHING**:" SECCOMP_MESSAGE_KILL_CONTENT "\n";
 190   WriteToStdErr(kSeccompKillError, sizeof(kSeccompKillError) - 1);
 191   // Make "pid" volatile so that we can see it on the stack in a minidump.
 192   volatile uint64_t my_pid = sys_getpid();
 193   volatile char* addr = reinterpret_cast<volatile char*>(my_pid & 0xFFF);
 194   *addr = '\0';
 195   for (;;)
 196     _exit(1);
 197 }
 198
 199 intptr_t SIGSYSFutexFailure(const struct arch_seccomp_data& args,
 200                             void* /* aux */) {
 201   static const char kSeccompFutexError[] =
 202       __FILE__ ":**CRASHING**:" SECCOMP_MESSAGE_FUTEX_CONTENT "\n";
 203   WriteToStdErr(kSeccompFutexError, sizeof(kSeccompFutexError) - 1);
 204   volatile int futex_op = args.args[1];
 205   volatile char* addr = reinterpret_cast<volatile char*>(futex_op & 0xFFF);
 206   *addr = '\0';
 207   for (;;)
 208     _exit(1);
 209 }
 210
 211 intptr_t SIGSYSSchedHandler(const struct arch_seccomp_data& args,
 212                             void* aux) {
 213   switch (args.nr) {
 214     case __NR_sched_getaffinity:
 215     case __NR_sched_getattr:
 216     case __NR_sched_getparam:
 217     case __NR_sched_getscheduler:
 218     case __NR_sched_rr_get_interval:
 219     case __NR_sched_setaffinity:
 220     case __NR_sched_setattr:
 221     case __NR_sched_setparam:
 222     case __NR_sched_setscheduler:
 223       const pid_t tid = sys_gettid();
 224       // The first argument is the pid.  If is our thread id, then replace it
 225       // with 0, which is equivalent and allowed by the policy.
 226       if (args.args[0] == static_cast<uint64_t>(tid)) {
 227         return Syscall::Call(args.nr,
 228                              0,
 229                              static_cast<intptr_t>(args.args[1]),
 230                              static_cast<intptr_t>(args.args[2]),
 231                              static_cast<intptr_t>(args.args[3]),
 232                              static_cast<intptr_t>(args.args[4]),
 233                              static_cast<intptr_t>(args.args[5]));
 234       }
 235       break;
 236   }
 237
 238   CrashSIGSYS_Handler(args, aux);
 239
 240   // Should never be reached.
 241   RAW_CHECK(false);
 242   return -ENOSYS;
 243 }
 244
 245 bpf_dsl::ResultExpr CrashSIGSYS() {
 246   return bpf_dsl::Trap(CrashSIGSYS_Handler, NULL);
 247 }
 248
 249 bpf_dsl::ResultExpr CrashSIGSYSClone() {
 250   return bpf_dsl::Trap(SIGSYSCloneFailure, NULL);
 251 }
 252
 253 bpf_dsl::ResultExpr CrashSIGSYSPrctl() {
 254   return bpf_dsl::Trap(SIGSYSPrctlFailure, NULL);
 255 }
 256
 257 bpf_dsl::ResultExpr CrashSIGSYSIoctl() {
 258   return bpf_dsl::Trap(SIGSYSIoctlFailure, NULL);
 259 }
 260
 261 bpf_dsl::ResultExpr CrashSIGSYSKill() {
 262   return bpf_dsl::Trap(SIGSYSKillFailure, NULL);
 263 }
 264
 265 bpf_dsl::ResultExpr CrashSIGSYSFutex() {
 266   return bpf_dsl::Trap(SIGSYSFutexFailure, NULL);
 267 }
 268
 269 bpf_dsl::ResultExpr RewriteSchedSIGSYS() {
 270   return bpf_dsl::Trap(SIGSYSSchedHandler, NULL);
 271 }
 272
 273 const char* GetErrorMessageContentForTests() {
 274   return SECCOMP_MESSAGE_COMMON_CONTENT;
 275 }
 276
 277 const char* GetCloneErrorMessageContentForTests() {
 278   return SECCOMP_MESSAGE_CLONE_CONTENT;
 279 }
 280
 281 const char* GetPrctlErrorMessageContentForTests() {
 282   return SECCOMP_MESSAGE_PRCTL_CONTENT;
 283 }
 284
 285 const char* GetIoctlErrorMessageContentForTests() {
 286   return SECCOMP_MESSAGE_IOCTL_CONTENT;
 287 }
 288
 289 const char* GetKillErrorMessageContentForTests() {
 290   return SECCOMP_MESSAGE_KILL_CONTENT;
 291 }
 292
 293 const char* GetFutexErrorMessageContentForTests() {
 294   return SECCOMP_MESSAGE_FUTEX_CONTENT;
 295 }
 296
 297 }  // namespace sandbox.