hwasan: Align n_namesz and n_descsz to 4 when reading notes.

[pcc]

Summary

There is no requirement for the producer of a note to include the note
alignment in these fields. As a result we can end up missing the HWASAN note
if one of the other notes in the binary has the alignment missing.

[eugenis]

LGTM

compiler-rt/lib/hwasan/hwasan.cpp

static void InitGlobalsFromPhdrs(ElfW(Addr) base, const ElfW(Phdr) * phdr,
   for (unsigned i = 0; i != phnum; ++i) {
     if (phdr[i].p_type != PT_NOTE)
       continue;
     const char *note = reinterpret_cast<const char *>(base + phdr[i].p_vaddr);
     const char *nend = note + phdr[i].p_memsz;
     while (note < nend) {
       auto *nhdr = reinterpret_cast<const ElfW(Nhdr) *>(note);
       const char *name = note + sizeof(ElfW(Nhdr));
-      const char *desc = name + nhdr->n_namesz;
+      const char *desc = name + RoundUpTo(nhdr->n_namesz, 4);
       if (nhdr->n_type != NT_LLVM_HWASAN_GLOBALS ||
           internal_strcmp(name, "LLVM") != 0) {
-        note = desc + nhdr->n_descsz;
+        note = desc + RoundUpTo(nhdr->n_descsz, 4);
         continue;
       }
 
       // Only libraries with instrumented globals need to be checked against the
       // code model since they use relocations that aren't checked at link time.
       CheckCodeModel(base, phdr, phnum);
 
       auto *global_note = reinterpret_cast<const hwasan_global_note *>(desc);