hwasan: Add a code model check for tagged globals.

[pcc]

Summary

See D65364 for the code model requirements for tagged globals. Because
of the relocations used these requirements cannot be checked at link
time so they must be checked at runtime.

[eugenis]

LGTM

compiler-rt/lib/hwasan/hwasan.cpp

 
 enum { NT_LLVM_HWASAN_GLOBALS = 3 };
 
 struct hwasan_global_note {
   s32 begin_relptr;
   s32 end_relptr;
 };
 
+// Check that the given library meets the code model requirements for tagged
+// globals. These properties are not checked at link time so they need to be
+// checked at runtime.
+static void CheckCodeModel(ElfW(Addr) base, const ElfW(Phdr) * phdr,
+                           ElfW(Half) phnum) {
+  ElfW(Addr) min_addr = -1ull, max_addr = 0;
+  for (unsigned i = 0; i != phnum; ++i) {
+    if (phdr[i].p_type != PT_LOAD)
+      continue;
+    ElfW(Addr) lo = base + phdr[i].p_vaddr, hi = lo + phdr[i].p_memsz;
+    if (min_addr > lo)
+      min_addr = lo;
+    if (max_addr < hi)
+      max_addr = hi;
+  }
+
+  if (max_addr - min_addr > 1ull << 32) {
+    Report("FATAL: HWAddressSanitizer: library size exceeds 2^32\n");
+    Die();
+  }
+  if (max_addr > 1ull << 48) {
+    Report("FATAL: HWAddressSanitizer: library loaded above address 2^48\n");
+    Die();
+  }
+}
+
 static void InitGlobalsFromPhdrs(ElfW(Addr) base, const ElfW(Phdr) * phdr,
                                  ElfW(Half) phnum) {
-  for (; phnum != 0; ++phdr, --phnum) {
-    if (phdr->p_type != PT_NOTE)
+  for (unsigned i = 0; i != phnum; ++i) {
+    if (phdr[i].p_type != PT_NOTE)
       continue;
-    const char *note = reinterpret_cast<const char *>(base + phdr->p_vaddr);
-    const char *nend = note + phdr->p_memsz;
+    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;
       if (nhdr->n_type != NT_LLVM_HWASAN_GLOBALS ||
           internal_strcmp(name, "LLVM") != 0) {
         note = desc + nhdr->n_descsz;
         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);
       auto *global_begin = reinterpret_cast<const hwasan_global *>(
           note + global_note->begin_relptr);
       auto *global_end = reinterpret_cast<const hwasan_global *>(
           note + global_note->end_relptr);
       InitGlobals(global_begin, global_end);
       return;
     }