1 // Copyright 2017 the V8 project 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 // PLEASE READ BEFORE CHANGING THIS FILE!
6 //
7 // This file implements the out of bounds signal handler for
8 // WebAssembly. Signal handlers are notoriously difficult to get
9 // right, and getting it wrong can lead to security
10 // vulnerabilities. In order to minimize this risk, here are some
11 // rules to follow.
12 //
13 // 1. Do not introduce any new external dependencies. This file needs
14 //    to be self contained so it is easy to audit everything that a
15 //    signal handler might do.
16 //
17 // 2. Any changes must be reviewed by someone from the crash reporting
18 //    or security team. See OWNERS for suggested reviewers.
19 //
20 // For more information, see https://goo.gl/yMeyUY.
21 //
22 // This file contains most of the code that actually runs in a signal handler
23 // context. Some additional code is used both inside and outside the signal
24 // handler. This code can be found in handler-shared.cc.
25 
26 #include "src/trap-handler/trap-handler-internal.h"
27 #include "src/trap-handler/trap-handler.h"
28 
29 namespace v8 {
30 namespace internal {
31 namespace trap_handler {
32 
33 #if V8_TRAP_HANDLER_SUPPORTED
34 
35 // This function contains the platform independent portions of fault
36 // classification.
TryFindLandingPad(uintptr_t fault_addr,uintptr_t * landing_pad)37 bool TryFindLandingPad(uintptr_t fault_addr, uintptr_t* landing_pad) {
38   // TODO(eholk): broad code range check
39 
40   // Taking locks in a signal handler is risky because a fault in the signal
41   // handler could lead to a deadlock when attempting to acquire the lock
42   // again. We guard against this case with g_thread_in_wasm_code. The lock
43   // may only be taken when not executing Wasm code (an assert in
44   // MetadataLock's constructor ensures this). This signal handler will bail
45   // out before trying to take the lock if g_thread_in_wasm_code is not set.
46   MetadataLock lock_holder;
47 
48   for (size_t i = 0; i < gNumCodeObjects; ++i) {
49     const CodeProtectionInfo* data = gCodeObjects[i].code_info;
50     if (data == nullptr) {
51       continue;
52     }
53     const Address base = data->base;
54 
55     if (fault_addr >= base && fault_addr < base + data->size) {
56       // Hurray, we found the code object. Check for protected addresses.
57       const ptrdiff_t offset = fault_addr - base;
58 
59       for (unsigned i = 0; i < data->num_protected_instructions; ++i) {
60         if (data->instructions[i].instr_offset == offset) {
61           // Hurray again, we found the actual instruction.
62           *landing_pad = data->instructions[i].landing_offset + base;
63 
64           gRecoveredTrapCount.store(
65               gRecoveredTrapCount.load(std::memory_order_relaxed) + 1,
66               std::memory_order_relaxed);
67 
68           return true;
69         }
70       }
71     }
72   }
73   return false;
74 }
75 #endif  // V8_TRAP_HANDLER_SUPPORTED
76 
77 }  // namespace trap_handler
78 }  // namespace internal
79 }  // namespace v8
80