Add check to see if stack pointer is off the stack according to the memory

mappings when rating Linux exploitability.

R=ivanpe@chromium.org

Review URL: https://codereview.chromium.org/1286033002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1487 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/processor/exploitability_linux.cc

@@ -102,6 +102,7 @@ ExploitabilityRating ExploitabilityLinux::CheckPlatformExploitability() {
   // Check if the instruction pointer is in a valid instruction region
   // by finding if it maps to an executable part of memory.
   uint64_t instruction_ptr = 0;
+  uint64_t stack_ptr = 0;
 
   const MinidumpContext *context = exception->GetContext();
   if (context == NULL) {
@@ -115,8 +116,15 @@ ExploitabilityRating ExploitabilityLinux::CheckPlatformExploitability() {
     return EXPLOITABILITY_ERR_PROCESSING;
   }
 
+  // Getting the stack pointer.
+  if (!context->GetStackPointer(&stack_ptr)) {
+    BPLOG(INFO) << "Failed to retrieve stack pointer.";
+    return EXPLOITABILITY_ERR_PROCESSING;
+  }
+
   // Checking for the instruction pointer in a valid instruction region.
-  if (!this->InstructionPointerInCode(instruction_ptr)) {
+  if (!this->InstructionPointerInCode(instruction_ptr) ||
+       this->StackPointerOffStack(stack_ptr)) {
     return EXPLOITABILITY_HIGH;
   }
 
@@ -125,6 +133,22 @@ ExploitabilityRating ExploitabilityLinux::CheckPlatformExploitability() {
   return EXPLOITABILITY_INTERESTING;
 }
 
+bool ExploitabilityLinux::StackPointerOffStack(uint64_t stack_ptr) {
+  MinidumpLinuxMapsList *linux_maps_list = dump_->GetLinuxMapsList();
+  // Inconclusive if there are no mappings available.
+  if (!linux_maps_list) {
+    return false;
+  }
+  const MinidumpLinuxMaps *linux_maps =
+      linux_maps_list->GetLinuxMapsForAddress(stack_ptr);
+  // Checks if the stack pointer maps to a valid mapping and if the mapping
+  // is not the stack. If the mapping has no name, it is inconclusive whether
+  // it is off the stack.
+  return !linux_maps ||
+         (linux_maps->GetPathname().compare("") &&
+          linux_maps->GetPathname().compare("[stack]"));
+}
+
 bool ExploitabilityLinux::InstructionPointerInCode(uint64_t instruction_ptr) {
   // Get Linux memory mapping from /proc/self/maps. Checking whether the
   // region the instruction pointer is in has executable permission can tell

src/processor/exploitability_linux.h

@@ -58,6 +58,10 @@ class ExploitabilityLinux : public Exploitability {
   // This method checks the exception that triggered the creation of the
   // minidump and reports whether the exception suggests no exploitability.
   bool BenignCrashTrigger(const MDRawExceptionStream *raw_exception_stream);
+
+  // Checks if the stack pointer points to a memory mapping that is not
+  // labelled as the stack.
+  bool StackPointerOffStack(uint64_t stack_ptr);
 };
 
 }  // namespace google_breakpad

src/processor/exploitability_unittest.cc

@@ -127,6 +127,10 @@ TEST(ExploitabilityTest, TestLinuxEngine) {
             ExploitabilityFor("linux_inside_module_exe_region1.dmp"));
   ASSERT_EQ(google_breakpad::EXPLOITABILITY_INTERESTING,
             ExploitabilityFor("linux_inside_module_exe_region2.dmp"));
+  ASSERT_EQ(google_breakpad::EXPLOITABILITY_INTERESTING,
+            ExploitabilityFor("linux_stack_pointer_in_stack.dmp"));
+  ASSERT_EQ(google_breakpad::EXPLOITABILITY_HIGH,
+            ExploitabilityFor("linux_stack_pointer_in_module.dmp"));
 
 }
 }