Verify that the elf matches the expected arch.

To avoid a case where a malicious app might try and trick the system to
create an elf and register object that mismatches, always verify that they
are the same arch.

Test: Ran unit tests.
Change-Id: I66978e9e02f8e4f396856912e7019528ead4838e

3 files changed, 18 insertions, 1 deletions

diff --git a/libbacktrace/UnwindStack.cpp b/libbacktrace/UnwindStack.cpp
index 4e7f761ff..fe28eba41 100644
--- a/libbacktrace/UnwindStack.cpp
+++ b/libbacktrace/UnwindStack.cpp
@@ -49,6 +49,7 @@ bool Backtrace::Unwind(unwindstack::Regs* regs, BacktraceMap* back_map,
   unwindstack::Unwinder unwinder(MAX_BACKTRACE_FRAMES + num_ignore_frames, stack_map->stack_maps(),
                                  regs, stack_map->process_memory());
   unwinder.SetResolveNames(stack_map->ResolveNames());
+  stack_map->SetArch(regs->Arch());
   if (stack_map->GetJitDebug() != nullptr) {
     unwinder.SetJitDebug(stack_map->GetJitDebug(), regs->Arch());
   }
diff --git a/libbacktrace/UnwindStackMap.cpp b/libbacktrace/UnwindStackMap.cpp
index 52dd44192..9d15af2db 100644
--- a/libbacktrace/UnwindStackMap.cpp
+++ b/libbacktrace/UnwindStackMap.cpp
@@ -25,6 +25,7 @@
 #include <unwindstack/Elf.h>
 #include <unwindstack/MapInfo.h>
 #include <unwindstack/Maps.h>
+#include <unwindstack/Regs.h>
 
 #include "UnwindStackMap.h"
 
@@ -106,7 +107,17 @@ std::string UnwindStackMap::GetFunctionName(uint64_t pc, uint64_t* offset) {
     return "";
   }
 
-  unwindstack::Elf* elf = map_info->GetElf(process_memory());
+  if (arch_ == unwindstack::ARCH_UNKNOWN) {
+    if (pid_ == getpid()) {
+      arch_ = unwindstack::Regs::CurrentArch();
+    } else {
+      // Create a remote regs, to figure out the architecture.
+      std::unique_ptr<unwindstack::Regs> regs(unwindstack::Regs::RemoteGet(pid_));
+      arch_ = regs->Arch();
+    }
+  }
+
+  unwindstack::Elf* elf = map_info->GetElf(process_memory(), arch_);
 
   std::string name;
   uint64_t func_offset;
diff --git a/libbacktrace/UnwindStackMap.h b/libbacktrace/UnwindStackMap.h
index 039f4a289..e19b60565 100644
--- a/libbacktrace/UnwindStackMap.h
+++ b/libbacktrace/UnwindStackMap.h
@@ -30,6 +30,7 @@
 #if !defined(NO_LIBDEXFILE_SUPPORT)
 #include <unwindstack/DexFiles.h>
 #endif
+#include <unwindstack/Elf.h>
 #include <unwindstack/JitDebug.h>
 #include <unwindstack/Maps.h>
 
@@ -58,6 +59,8 @@ class UnwindStackMap : public BacktraceMap {
   unwindstack::DexFiles* GetDexFiles() { return dex_files_.get(); }
 #endif
 
+  void SetArch(unwindstack::ArchEnum arch) { arch_ = arch; }
+
  protected:
   uint64_t GetLoadBias(size_t index) override;
 
@@ -67,6 +70,8 @@ class UnwindStackMap : public BacktraceMap {
 #if !defined(NO_LIBDEXFILE_SUPPORT)
   std::unique_ptr<unwindstack::DexFiles> dex_files_;
 #endif
+
+  unwindstack::ArchEnum arch_ = unwindstack::ARCH_UNKNOWN;
 };
 
 class UnwindStackOfflineMap : public UnwindStackMap {