1 /*
2 * Copyright (C) 2020 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "incfs_support/signal_handling.h"
18
19 #if defined(__BIONIC__) && !INCFS_SUPPORT_DISABLED
20
21 #include <errno.h>
22
23 namespace incfs {
24
enableSignal(int code)25 static void enableSignal(int code) {
26 sigset_t allowed;
27 sigemptyset(&allowed);
28 sigaddset(&allowed, code);
29 pthread_sigmask(SIG_UNBLOCK, &allowed, nullptr);
30 }
31
~ScopedJmpBuf()32 ScopedJmpBuf::~ScopedJmpBuf() { SignalHandler::mJmpBuf = mPrev; }
33
instance()34 SignalHandler& SignalHandler::instance() {
35 static SignalHandler self;
36 return self;
37 }
38
SignalHandler()39 SignalHandler::SignalHandler() {
40 const struct sigaction action = {
41 .sa_sigaction = &handler,
42 .sa_flags = SA_SIGINFO,
43 };
44 if (sigaction(SIGBUS, &action, &mOldSigaction)) {
45 LOG_ALWAYS_FATAL("sigaction(SIGBUS) failed: %d", errno);
46 // not much can be done now
47 return;
48 }
49
50 // ensure SIGBUS is unblocked, so the process won't get insta-killed
51 enableSignal(SIGBUS);
52 }
53
handler(int sig,siginfo_t * info,void * ucontext)54 void SignalHandler::handler(int sig, siginfo_t* info, void* ucontext) {
55 if (sig != SIGBUS) {
56 LOG_FATAL("SIGBUS handler called for unexpected signal %d", sig);
57 return;
58 }
59
60 if (!mJmpBuf.armed) {
61 // No error handler installed - run the previous one
62 if (mOldSigaction.sa_handler == SIG_DFL) {
63 // reset the action to default and re-raise the signal. It will kill the
64 // process
65 signal(sig, SIG_DFL);
66 raise(sig);
67 return;
68 }
69 if (mOldSigaction.sa_handler == SIG_IGN) {
70 // ignoring SIGBUS won't help us much, as we'll get back right here after
71 // retrying.
72 return;
73 }
74 if (mOldSigaction.sa_flags & SA_SIGINFO) {
75 mOldSigaction.sa_sigaction(sig, info, ucontext);
76 } else {
77 mOldSigaction.sa_handler(sig);
78 }
79 // Returning from a signal handler for SIGBUS is undefined, but if it
80 // happens better to at least forward that undefined thing further. Who are
81 // we to argue with the user?
82 return;
83 }
84
85 // restore SIGBUS as signal handling blocks it before running the callback
86 enableSignal(SIGBUS);
87
88 longjmp(mJmpBuf.buf, 1);
89 }
90
91 } // namespace incfs
92
93 #endif
94