[PATCH] D57081: [libunwind] Don't abort if encoutering invalid .eh_frame_hdr

[Petr Hosek via Phabricator]

phosek created this revision.
phosek added reviewers: mstorsjo, echristo.
Herald added subscribers: libcxx-commits, ldionne, christof.

Recent Linux kernel release has introduced a bug as part of the ORC
rollout where the vDSO has a valid .eh_frame section, but it's missing
the .eh_frame_hdr section and GNU_EH_FRAME segment has zero size. This
causes libunwind to abort which breaks programs that use libunwind.

The other unwinder implementation (libgcc, non-gnu) instead silently
bail out unless being compiled as debug. This change modifies libunwind
to use the same strategy.


Repository:
  rUNW libunwind

https://reviews.llvm.org/D57081

Files:
  libunwind/src/AddressSpace.hpp
  libunwind/src/EHHeaderParser.hpp


Index: libunwind/src/EHHeaderParser.hpp
===================================================================
--- libunwind/src/EHHeaderParser.hpp
+++ libunwind/src/EHHeaderParser.hpp
@@ -35,7 +35,7 @@
     uint8_t table_enc;
   };
 
-  static void decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
+  static bool decodeEHHdr(A &addressSpace, pint_t ehHdrStart, pint_t ehHdrEnd,
                           EHHeaderInfo &ehHdrInfo);
   static bool findFDE(A &addressSpace, pint_t pc, pint_t ehHdrStart,
                       uint32_t sectionLength,
@@ -52,12 +52,14 @@
 };
 
 template <typename A>
-void EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
+bool EHHeaderParser<A>::decodeEHHdr(A &addressSpace, pint_t ehHdrStart,
                                     pint_t ehHdrEnd, EHHeaderInfo &ehHdrInfo) {
   pint_t p = ehHdrStart;
   uint8_t version = addressSpace.get8(p++);
-  if (version != 1)
-    _LIBUNWIND_ABORT("Unsupported .eh_frame_hdr version");
+  if (version != 1) {
+    _LIBUNWIND_LOG0("Unsupported .eh_frame_hdr version");
+    return false;
+  }
 
   uint8_t eh_frame_ptr_enc = addressSpace.get8(p++);
   uint8_t fde_count_enc = addressSpace.get8(p++);
@@ -70,6 +72,8 @@
           ? 0
           : addressSpace.getEncodedP(p, ehHdrEnd, fde_count_enc, ehHdrStart);
   ehHdrInfo.table = p;
+
+  return true;
 }
 
 template <typename A>
@@ -101,7 +105,9 @@
   pint_t ehHdrEnd = ehHdrStart + sectionLength;
 
   EHHeaderParser<A>::EHHeaderInfo hdrInfo;
-  EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd, hdrInfo);
+  if (!EHHeaderParser<A>::decodeEHHdr(addressSpace, ehHdrStart, ehHdrEnd,
+                                      hdrInfo))
+    return false;
 
   size_t tableEntrySize = getTableEntrySize(hdrInfo.table_enc);
   pint_t tableEntry;
Index: libunwind/src/AddressSpace.hpp
===================================================================
--- libunwind/src/AddressSpace.hpp
+++ libunwind/src/AddressSpace.hpp
@@ -526,7 +526,7 @@
               object_length = phdr->p_memsz;
               found_obj = true;
             }
-          } else if (phdr->p_type == PT_GNU_EH_FRAME) {
+          } else if (phdr->p_type == PT_GNU_EH_FRAME && phdr->p_memsz > 0) {
             EHHeaderParser<LocalAddressSpace>::EHHeaderInfo hdrInfo;
             uintptr_t eh_frame_hdr_start = pinfo->dlpi_addr + phdr->p_vaddr;
 #if defined(__ANDROID__)
@@ -535,11 +535,11 @@
 #endif
             cbdata->sects->dwarf_index_section = eh_frame_hdr_start;
             cbdata->sects->dwarf_index_section_length = phdr->p_memsz;
-            EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
+            found_hdr = EHHeaderParser<LocalAddressSpace>::decodeEHHdr(
                 *cbdata->addressSpace, eh_frame_hdr_start, phdr->p_memsz,
                 hdrInfo);
-            cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
-            found_hdr = true;
+            if (found_hdr)
+              cbdata->sects->dwarf_section = hdrInfo.eh_frame_ptr;
           }
         }
 


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