[llvm-readelf] - Report a warning when .hash section contains a chain with a cycle.

[grimar]

Summary

It is possible to craft a .hash section that triggers an infinite loop
in llvm-readelf code. This patch fixes the issue and introduces
a warning.

[MaskRay]

test/tools/llvm-readobj/elf-hash-symbols.test

365

an entry of the bucket array points to a cycle

391

Suggested wording:

llvm-readelf will read the hash table from the file offset p_offset + (p_vaddr - DT_HASH) = p_offset + (0 - 0) = p_offset, which is the start of PT_LOAD, i.e. the file offset of .hash

[jhenderson]

test/tools/llvm-readobj/elf-hash-symbols.test

365

Also "when a hash table" or similar.

I think combining the two suggests:

"Show that we report a warning for a hash table which contains an entry of the bucket array pointing to a cycle."

tools/llvm-readobj/ELFDumper.cpp

3446

Perhaps worth giving more context to this message, i.e. something about a cycle being detected linking which buckets.

[grimar]

• Addressed review comments.

[jhenderson]

LGTM, with one nit.

test/tools/llvm-readobj/elf-hash-symbols.test

393

Nit: missing trailing full stop.

test/tools/llvm-readobj/elf-hash-symbols.test

Sections:
       - Section: .dynamic
       - Section: .text.foo
   - Type:  PT_DYNAMIC
     Flags: [ PF_R ]
     VAddr: 0x1000
     PAddr: 0x1000
     Sections:
       - Section: .dynamic
+
+## Show that we report a warning when .hash section contains a chain with a cycle.
+
+# RUN: yaml2obj --docnum=6 %s -o %t6.so
+# RUN: llvm-readelf --hash-symbols %t6.so 2>&1 | FileCheck %s -DFILE=%t6.so --check-prefix=BROKEN
+
+# BROKEN:      Symbol table of .hash for image:
+# BROKEN-NEXT:  Num Buc:    Value  Size   Type   Bind Vis      Ndx Name
+# BROKEN-NEXT:    1   0: 00000000     0 NOTYPE  LOCAL  DEFAULT UND aaa
+# BROKEN: warning: '[[FILE]]': .hash section is invalid
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_386
+Sections:
+  - Name:    .hash
+    Type:    SHT_HASH
+    Link:    .dynsym
+    Bucket:  [ 1 ]
+    Chain:   [ 1, 1 ]
+  - Name:  .dynamic
+    Type:  SHT_DYNAMIC
+    Entries:
+## PT_LOAD's p_vaddr is 0x0. PT_LOAD's p_offset = 0x1bc. DT_HASH value is 0x0. 
+## llvm-readelf will read .hash content from p_offset + (p_vaddr - DT_HASH value) = 0x1bc.
+## This matches the file offset of the .hash section.
+      - Tag:   DT_HASH
+        Value: 0x0
+DynamicSymbols:
+  - Name:    aaa
+  - Name:    bbb
+ProgramHeaders:
+  - Type:  PT_LOAD
+    Sections:
+      - Section: .hash
+      - Section: .dynamic

tools/llvm-readobj/ELFDumper.cpp

else
       OS << "  Num Buc:    Value  Size   Type   Bind Vis      Ndx Name";
     OS << "\n";
 
     auto Buckets = SysVHash->buckets();
     auto Chains = SysVHash->chains();
     for (uint32_t Buc = 0; Buc < SysVHash->nbucket; Buc++) {
       if (Buckets[Buc] == ELF::STN_UNDEF)
         continue;
+      std::vector<bool> Visited(SysVHash->nchain);
       for (uint32_t Ch = Buckets[Buc]; Ch < SysVHash->nchain; Ch = Chains[Ch]) {
         if (Ch == ELF::STN_UNDEF)
           break;
+
+        if (Visited[Ch]) {
+          reportWarning(createError(".hash section is invalid"), FileName);
+          break;
+        }
+
         printHashedSymbol(Obj, &DynSyms[0], Ch, StringTable, Buc);
+        Visited[Ch] = true;
       }
     }
   }
 
   // Try printing .gnu.hash
   if (auto GnuHash = this->dumper()->getGnuHashTable()) {
     OS << "\n Symbol table of .gnu.hash for image:\n";
     if (ELFT::Is64Bits)