From 87315e9d2fdf6c7a6d876e63f844299f982a5b75 Mon Sep 17 00:00:00 2001
From: Colin Cross <ccross@android.com>
Date: Wed, 20 Mar 2019 16:02:54 -0700
Subject: [PATCH] Catch SIGBUS in HeapWalker

SIGBUS shouldn't happen, since all of the regions being walked
were previously read out of /prod/pid/maps, but it seems to happen
rarely.  Catch it so it can produce a better log message.

Bug: 128983715
Test: atest memunreachable_test
Change-Id: I82d3941a382a0451c0dda12f5eb849ad8d697bc9
---
 libmemunreachable/HeapWalker.cpp        |  2 +-
 libmemunreachable/HeapWalker.h          | 12 +++++++---
 libmemunreachable/ScopedSignalHandler.h | 30 +++++++++++++++++++------
 3 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/libmemunreachable/HeapWalker.cpp b/libmemunreachable/HeapWalker.cpp
index e11f0798a..7cae04869 100644
--- a/libmemunreachable/HeapWalker.cpp
+++ b/libmemunreachable/HeapWalker.cpp
@@ -207,6 +207,6 @@ void HeapWalker::HandleSegFault(ScopedSignalHandler& handler, int signal, siginf
   }
 }
 
-ScopedSignalHandler::SignalFn ScopedSignalHandler::handler_;
+Allocator<ScopedSignalHandler::SignalFnMap>::unique_ptr ScopedSignalHandler::handler_map_;
 
 }  // namespace android
diff --git a/libmemunreachable/HeapWalker.h b/libmemunreachable/HeapWalker.h
index 9e3db080d..f00bccaaa 100644
--- a/libmemunreachable/HeapWalker.h
+++ b/libmemunreachable/HeapWalker.h
@@ -52,7 +52,8 @@ class HeapWalker {
         allocation_bytes_(0),
         roots_(allocator),
         root_vals_(allocator),
-        segv_handler_(),
+        sigsegv_handler_(allocator),
+        sigbus_handler_(allocator),
         walking_ptr_(0),
         walking_range_{0, 0},
         segv_logged_(false),
@@ -62,10 +63,14 @@ class HeapWalker {
     valid_mappings_range_.end = 0;
     valid_mappings_range_.begin = ~valid_allocations_range_.end;
 
-    segv_handler_.install(
+    sigsegv_handler_.install(
         SIGSEGV, [=](ScopedSignalHandler& handler, int signal, siginfo_t* siginfo, void* uctx) {
           this->HandleSegFault(handler, signal, siginfo, uctx);
         });
+    sigbus_handler_.install(
+        SIGBUS, [=](ScopedSignalHandler& handler, int signal, siginfo_t* siginfo, void* uctx) {
+          this->HandleSegFault(handler, signal, siginfo, uctx);
+        });
   }
 
   ~HeapWalker() {}
@@ -106,7 +111,8 @@ class HeapWalker {
   allocator::vector<Range> roots_;
   allocator::vector<uintptr_t> root_vals_;
 
-  ScopedSignalHandler segv_handler_;
+  ScopedSignalHandler sigsegv_handler_;
+  ScopedSignalHandler sigbus_handler_;
   volatile uintptr_t walking_ptr_;
   Range walking_range_;
   bool segv_logged_;
diff --git a/libmemunreachable/ScopedSignalHandler.h b/libmemunreachable/ScopedSignalHandler.h
index 9e08a8ecc..ef4473f7a 100644
--- a/libmemunreachable/ScopedSignalHandler.h
+++ b/libmemunreachable/ScopedSignalHandler.h
@@ -24,6 +24,7 @@
 
 #include "android-base/macros.h"
 
+#include "Allocator.h"
 #include "log.h"
 
 namespace android {
@@ -32,17 +33,29 @@ class ScopedSignalHandler {
  public:
   using Fn = std::function<void(ScopedSignalHandler&, int, siginfo_t*, void*)>;
 
-  explicit ScopedSignalHandler() : signal_(-1) {}
+  explicit ScopedSignalHandler(Allocator<ScopedSignalHandler> allocator) : signal_(-1) {
+    if (handler_map_ == nullptr) {
+      Allocator<SignalFnMap> map_allocator = allocator;
+      handler_map_ = map_allocator.make_unique(allocator);
+    }
+  }
   ~ScopedSignalHandler() { reset(); }
 
   template <class F>
   void install(int signal, F&& f) {
     if (signal_ != -1) MEM_LOG_ALWAYS_FATAL("ScopedSignalHandler already installed");
 
-    handler_ = SignalFn([=](int signal, siginfo_t* si, void* uctx) { f(*this, signal, si, uctx); });
+    if (handler_map_->find(signal) != handler_map_->end()) {
+      MEM_LOG_ALWAYS_FATAL("ScopedSignalHandler already installed for %d", signal);
+    }
+
+    (*handler_map_)[signal] =
+        SignalFn([=](int signal, siginfo_t* si, void* uctx) { f(*this, signal, si, uctx); });
 
     struct sigaction act {};
-    act.sa_sigaction = [](int signal, siginfo_t* si, void* uctx) { handler_(signal, si, uctx); };
+    act.sa_sigaction = [](int signal, siginfo_t* si, void* uctx) {
+      ((*handler_map_)[signal])(signal, si, uctx);
+    };
     act.sa_flags = SA_SIGINFO;
 
     int ret = sigaction(signal, &act, &old_act_);
@@ -59,19 +72,22 @@ class ScopedSignalHandler {
       if (ret < 0) {
         MEM_ALOGE("failed to uninstall segfault handler");
       }
-      handler_ = SignalFn{};
+
+      handler_map_->erase(signal_);
+      if (handler_map_->empty()) {
+        handler_map_.reset();
+      }
       signal_ = -1;
     }
   }
 
  private:
   using SignalFn = std::function<void(int, siginfo_t*, void*)>;
+  using SignalFnMap = allocator::unordered_map<int, SignalFn>;
   DISALLOW_COPY_AND_ASSIGN(ScopedSignalHandler);
   int signal_;
   struct sigaction old_act_;
-  // TODO(ccross): to support multiple ScopedSignalHandlers handler_ would need
-  // to be a static map of signals to handlers, but allocated with Allocator.
-  static SignalFn handler_;
+  static Allocator<SignalFnMap>::unique_ptr handler_map_;
 };
 
 }  // namespace android