[Lldb-commits] [PATCH] D158312: [debugserver] align received mach exception data before accessing it as array of uint64_t's, fix UB sanitizer failure

[Jason Molenda via Phabricator via lldb-commits]

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The mach exception data received in debugserver is not aligned to a doubleword boundary.  Most of these were fixed in 2017 by Vedant (`[MachException] Avoid alignment UB, NFC`) but there was a codepath when debugserver logging is enabled where we would still access the mach exception data without aligning it first.  This has been causing failures on the sanitizer greendragon bot for the last few days from Jim's change in  https://reviews.llvm.org/D157556  where he is enabling LOG_EXCEPTIONS debugserver logging unconditionally (this should prob be in a self.TraceOn() conditional, or maybe not even be in the test - it looks like a debug print he forgot to remove) in the new test_shadow_listener test.

https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake-sanitized/

Simplest fix, and it's only done when LOG_EXCEPTIONS is enabled, is to align the data one-off for the logging.

I would have handed this to Jim to fix, but by the time I understood what the actual failure was, it was nothing to fix it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158312

Files:
  lldb/tools/debugserver/source/MacOSX/MachException.cpp


Index: lldb/tools/debugserver/source/MacOSX/MachException.cpp
===================================================================
--- lldb/tools/debugserver/source/MacOSX/MachException.cpp
+++ lldb/tools/debugserver/source/MacOSX/MachException.cpp
@@ -95,13 +95,20 @@
                            mach_exception_data_t exc_data,
                            mach_msg_type_number_t exc_data_count) {
   if (DNBLogCheckLogBit(LOG_EXCEPTIONS)) {
+    std::vector<uint64_t> exc_datas;
+    uint64_t tmp;
+    for (unsigned i = 0; i < exc_data_count; ++i) {
+      // Perform an unaligned copy.
+      memcpy(&tmp, &exc_data[i], sizeof(uint64_t));
+      exc_datas.push_back(tmp);
+    }
     DNBLogThreaded("::%s ( exc_port = 0x%4.4x, thd_port = 0x%4.4x, tsk_port = "
                    "0x%4.4x, exc_type = %d ( %s ), exc_data[%d] = { 0x%llx, "
                    "0x%llx })",
                    __FUNCTION__, exc_port, thread_port, task_port, exc_type,
                    MachException::Name(exc_type), exc_data_count,
-                   (uint64_t)(exc_data_count > 0 ? exc_data[0] : 0xBADDBADD),
-                   (uint64_t)(exc_data_count > 1 ? exc_data[1] : 0xBADDBADD));
+                   (uint64_t)(exc_data_count > 0 ? exc_datas[0] : 0xBADDBADD),
+                   (uint64_t)(exc_data_count > 1 ? exc_datas[1] : 0xBADDBADD));
   }
   g_message->exc_type = 0;
   g_message->exc_data.clear();


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