[Object/ELF] - Do not crash on invalid Header->e_shoff value.

[grimar]

Summary

sections_begin() may return unalignment pointer when Header->e_shoff isinvalid.
That may result in a crash in clients, for example we have one in LLD:

assert((PtrWord & ~PointerBitMask) == 0 &&
       "Pointer is not sufficiently aligned");

fails when trying to push_back Elf_Shdr* (unaligned) into TinyPtrVector.

Patch forces address to be aligned.

[grimar]

gnu archives seems does not like such innovations. I`ll reimplement this to do checks from lld side.

[grimar]

Will update in a minute.

[grimar]

• As suggested by Rafael, check only alignment of Header->e_shoff.

[• rafael]

LGTM with a nit.

include/llvm/Object/ELF.h

370

Can you use Elf_Shdr instead of uint in AlignOf? After all that is what we return a pointer to.

[grimar]

r283740

include/llvm/Object/ELF.h

static bool compareAddr(uint64_t VAddr, const Elf_Phdr_Impl<ELFT> *Phdr) {
   return VAddr < Phdr->p_vaddr;
 }
 
 template <class ELFT>
 const typename ELFFile<ELFT>::Elf_Shdr *ELFFile<ELFT>::section_begin() const {
   if (Header->e_shentsize != sizeof(Elf_Shdr))
     report_fatal_error(
         "Invalid section header entry size (e_shentsize) in ELF header");
+  if (Header->e_shoff & (AlignOf<typename ELFT::uint>::Alignment - 1))
+    report_fatal_error("Invalid address alignment of section headers");
   return reinterpret_cast<const Elf_Shdr *>(base() + Header->e_shoff);
 }
 
 template <class ELFT>
 const typename ELFFile<ELFT>::Elf_Shdr *ELFFile<ELFT>::section_end() const {
   return section_begin() + getNumSections();
 }
 

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 address alignment of section headers