[scudo] Workaround for uninitialized Bionic globals

[cryptoad]

Summary

Bionic doesn't initialize its globals early enough. This causes issues when
trying to access them from a preinit_array (b/25751302) or from another
constructor called before the libc one (b/68046352). __progname is initialized
after the other globals, so we can check its value to know if calling
getauxval is safe.

[alekseyshl]

lib/scudo/scudo_utils.cpp

110

So, hasHardwareCRC32ARMPosix() works fine, even that not all globals are initialized? Maybe the proper way is to repeat the check after globals are initialized (a lot more hassle, I know)?

[cryptoad]

lib/scudo/scudo_utils.cpp

110

I'll see what I can whip out regarding the 2nd part of the comment.

A few other words for the record:
hasHardwareCRC32ARMPosix will work if the application has access to /proc/self/auxv. Two reasons I see why it wouldn't: /proc is not mounted yet (which is the case for init) or the file is disallowed via selinux/seccompbpf/sandboxing in general. This doesn't involve the libc globals.
getauxval will work if the first dynamic memory allocation related call isn't prior to the initialization of the Bionic globals, as it loops through __libc_auxv which is NULL at this point.
Things work with other libcs (musl, glibc) AFAICT, and is only an issue for Bionic.

lib/scudo/scudo_utils.cpp

bool hasHardwareCRC32ARMPosix() {
   }
   internal_close(F);
   return (Entry.Tag == AT_HWCAP && (Entry.Value & HWCAP_CRC32) != 0);
 }
 # else
 bool hasHardwareCRC32ARMPosix() { return false; }
 # endif  // SANITIZER_POSIX
 
+// Bionic doesn't initialize its globals early enough. This causes issues when
+// trying to access them from a preinit_array (b/25751302) or from another
+// constructor called before the libc one (b/68046352). __progname is
+// initialized after the other globals, so we can check its value to know if
+// calling getauxval is safe.
+extern "C" SANITIZER_WEAK_ATTRIBUTE char *__progname;
+INLINE bool areBionicGlobalsInitialized() {
+  return !SANITIZER_ANDROID || (&__progname && __progname);
+}
+
 bool hasHardwareCRC32() {
-  if (&getauxval)
+  if (&getauxval && areBionicGlobalsInitialized())
     return !!(getauxval(AT_HWCAP) & HWCAP_CRC32);
   return hasHardwareCRC32ARMPosix();
 }
 #else
 bool hasHardwareCRC32() { return false; }
 #endif  // defined(__x86_64__) || defined(__i386__)
 
 }  // namespace __scudo