[Object/ELF] - Check Header->e_shoff value earlier and do not crash.

[grimar]

Summary

I had to revert D25368 (r283858, r283740) because it was the reason of UBSan failture:
(http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/17075)

Exit Code: 1

Command Output (stderr):

/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/test/Object/invalid.test:70:32: error: expected string not found in input
INVALID-SEC-ADDRESS-ALIGNMENT: Invalid address alignment of section headers

^

<stdin>:1:1: note: scanning from here
/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/include/llvm/Object/ELF.h:412:7: runtime error: upcast of misaligned address 0x000002d8b899 for type 'llvm::object::Elf_Shdr_Impl<llvm::object::ELFType<llvm::support::endianness::little, true> >', which requires 2 byte alignment
^
<stdin>:1:125: note: possible intended match here
/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/include/llvm/Object/ELF.h:412:7: runtime error: upcast of misaligned address 0x000002d8b899 for type 'llvm::object::Elf_Shdr_Impl<llvm::object::ELFType<llvm::support::endianness::little, true> >', which requires 2 byte alignment

Problem is seems to be that on the moment of following call, Section pointer is unaligned:

ELFFile<ELFT>::getStringTable(const Elf_Shdr *Section) const

Patch moves the alignment check before such call to fix the issue.

[• rafael]

LGTM

include/llvm/Object/ELF.h

ELFFile<ELFT>::ELFFile(StringRef Object, std::error_code &EC)
   const uint64_t SectionTableOffset = Header->e_shoff;
 
   if (SectionTableOffset + sizeof(Elf_Shdr) > FileSize) {
     // Section header table goes past end of file!
     EC = object_error::parse_failed;
     return;
   }
 
+  if (SectionTableOffset & (AlignOf<Elf_Shdr>::Alignment - 1)) {
+    // Invalid address alignment of section headers
+    EC = object_error::parse_failed;
+    return;
+  }
+
   // The getNumSections() call below depends on SectionHeaderTable being set.
   SectionHeaderTable =
     reinterpret_cast<const Elf_Shdr *>(base() + SectionTableOffset);
   const uint64_t SectionTableSize = getNumSections() * Header->e_shentsize;
 
   if (SectionTableOffset + SectionTableSize > FileSize) {
     // Section table goes past end of file!
     EC = object_error::parse_failed;

test/Object/invalid.test

 RUN:   FileCheck --check-prefix=INVALID-EXT-SYMTAB-INDEX %s
 INVALID-EXT-SYMTAB-INDEX: Invalid symbol table index
 
 RUN: not llvm-readobj -r %p/Inputs/invalid-relocation-sec-sh_offset.elf-i386 2>&1 | \
 RUN:   FileCheck --check-prefix=INVALID-RELOC-SH-OFFSET %s
 RUN: not llvm-readobj -r %p/Inputs/invalid-relocation-sec-sh_offset.elf-x86-64 2>&1 | \
 RUN:   FileCheck --check-prefix=INVALID-RELOC-SH-OFFSET %s
 INVALID-RELOC-SH-OFFSET: Invalid data was encountered while parsing the file
+
+RUN: not llvm-readobj -t %p/Inputs/invalid-sections-address-alignment.x86-64 2>&1 | \
+RUN:   FileCheck --check-prefix=INVALID-SEC-ADDRESS-ALIGNMENT %s
+INVALID-SEC-ADDRESS-ALIGNMENT: Invalid data was encountered while parsing the file