Merge "Add cause message when stack overflow is detected."

debuggerd/debuggerd_test.cpp

@@ -1099,3 +1099,30 @@ TEST(tombstoned, interceptless_backtrace) {
   // This should be good enough, though...
   ASSERT_LT(diff, 10) << "too many new tombstones; is something crashing in the background?";
 }
+
+static __attribute__((__noinline__)) void overflow_stack(void* p) {
+  void* buf[1];
+  buf[0] = p;
+  static volatile void* global = buf;
+  if (global) {
+    global = buf;
+    overflow_stack(&buf);
+  }
+}
+
+TEST_F(CrasherTest, stack_overflow) {
+  int intercept_result;
+  unique_fd output_fd;
+  StartProcess([]() { overflow_stack(nullptr); });
+
+  StartIntercept(&output_fd);
+  FinishCrasher();
+  AssertDeath(SIGSEGV);
+  FinishIntercept(&intercept_result);
+
+  ASSERT_EQ(1, intercept_result) << "tombstoned reported failure";
+
+  std::string result;
+  ConsumeFd(std::move(output_fd), &result);
+  ASSERT_MATCH(result, R"(Cause: stack pointer[^\n]*stack overflow.\n)");
+}

debuggerd/libdebuggerd/tombstone.cpp

@@ -86,7 +86,39 @@ static void dump_timestamp(log_t* log, time_t time) {
   _LOG(log, logtype::HEADER, "Timestamp: %s\n", buf);
 }
 
-static void dump_probable_cause(log_t* log, const siginfo_t* si, unwindstack::Maps* maps) {
+static std::string get_stack_overflow_cause(uint64_t fault_addr, uint64_t sp,
+                                            unwindstack::Maps* maps) {
+  static constexpr uint64_t kMaxDifferenceBytes = 256;
+  uint64_t difference;
+  if (sp >= fault_addr) {
+    difference = sp - fault_addr;
+  } else {
+    difference = fault_addr - sp;
+  }
+  if (difference <= kMaxDifferenceBytes) {
+    // The faulting address is close to the current sp, check if the sp
+    // indicates a stack overflow.
+    // On arm, the sp does not get updated when the instruction faults.
+    // In this case, the sp will still be in a valid map, which is the
+    // last case below.
+    // On aarch64, the sp does get updated when the instruction faults.
+    // In this case, the sp will be in either an invalid map if triggered
+    // on the main thread, or in a guard map if in another thread, which
+    // will be the first case or second case from below.
+    unwindstack::MapInfo* map_info = maps->Find(sp);
+    if (map_info == nullptr) {
+      return "stack pointer is in a non-existent map; likely due to stack overflow.";
+    } else if ((map_info->flags & (PROT_READ | PROT_WRITE)) != (PROT_READ | PROT_WRITE)) {
+      return "stack pointer is not in a rw map; likely due to stack overflow.";
+    } else if ((sp - map_info->start) <= kMaxDifferenceBytes) {
+      return "stack pointer is close to top of stack; likely stack overflow.";
+    }
+  }
+  return "";
+}
+
+static void dump_probable_cause(log_t* log, const siginfo_t* si, unwindstack::Maps* maps,
+                                unwindstack::Regs* regs) {
   std::string cause;
   if (si->si_signo == SIGSEGV && si->si_code == SEGV_MAPERR) {
     if (si->si_addr < reinterpret_cast<void*>(4096)) {
@@ -101,11 +133,16 @@ static void dump_probable_cause(log_t* log, const siginfo_t* si, unwindstack::Ma
       cause = "call to kuser_memory_barrier";
     } else if (si->si_addr == reinterpret_cast<void*>(0xffff0f60)) {
       cause = "call to kuser_cmpxchg64";
+    } else {
+      cause = get_stack_overflow_cause(reinterpret_cast<uint64_t>(si->si_addr), regs->sp(), maps);
     }
   } else if (si->si_signo == SIGSEGV && si->si_code == SEGV_ACCERR) {
-    unwindstack::MapInfo* map_info = maps->Find(reinterpret_cast<uint64_t>(si->si_addr));
+    uint64_t fault_addr = reinterpret_cast<uint64_t>(si->si_addr);
+    unwindstack::MapInfo* map_info = maps->Find(fault_addr);
     if (map_info != nullptr && map_info->flags == PROT_EXEC) {
       cause = "execute-only (no-read) memory access error; likely due to data in .text.";
+    } else {
+      cause = get_stack_overflow_cause(fault_addr, regs->sp(), maps);
     }
   } else if (si->si_signo == SIGSYS && si->si_code == SYS_SECCOMP) {
     cause = StringPrintf("seccomp prevented call to disallowed %s system call %d", ABI_STRING,
@@ -447,7 +484,7 @@ static bool dump_thread(log_t* log, unwindstack::Unwinder* unwinder, const Threa
 
   if (thread_info.siginfo) {
     dump_signal_info(log, thread_info, unwinder->GetProcessMemory().get());
-    dump_probable_cause(log, thread_info.siginfo, unwinder->GetMaps());
+    dump_probable_cause(log, thread_info.siginfo, unwinder->GetMaps(), thread_info.registers.get());
   }
 
   if (primary_thread) {