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 trap handler for
8// WebAssembly. Trap 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// trap 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 trap handler
23// context. Some additional code is used both inside and outside the trap
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
29namespace v8 {
30namespace internal {
31namespace trap_handler {
32
33#if V8_TRAP_HANDLER_SUPPORTED
34
35// This function contains the platform independent portions of fault
36// classification.
37bool TryFindLandingPad(uintptr_t fault_addr, uintptr_t* landing_pad) {
38 // TODO(eholk): broad code range check
39
40 // Taking locks in the trap handler is risky because a fault in the trap
41 // handler itself could lead to a deadlock when attempting to acquire the
42 // lock again. We guard against this case with g_thread_in_wasm_code. The
43 // lock may only be taken when not executing Wasm code (an assert in
44 // MetadataLock's constructor ensures this). The trap 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