A mechanism to identify/forbid/"rewrite" non-temporal instructions (and other)

src/trusted/validator_arm/ncvalidate.cc

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <climits>
 #include <limits>
 #include <vector>
 
@@ skipping 125 matching lines @@
   *is_position_independent = validator.is_position_independent();
   if (!success) return 2;  // for compatibility with old validator
   return 0;
 }
 
 static NaClValidationStatus ApplyValidatorArm(
     uintptr_t guest_addr,
     uint8_t *data,
     size_t size,
     int stubout_mode,
+    uint32_t flags,
     int readonly_text,
     const NaClCPUFeatures *cpu_features,
     const struct NaClValidationMetadata *metadata,
     struct NaClValidationCache *cache) {
   // The ARM validator never modifies the text, so this flag can be ignored.
   UNREFERENCED_PARAMETER(readonly_text);
+  UNREFERENCED_PARAMETER(flags);

[JF, 2015/07/29 00:08:02]

I'd rather CHECK(flags == 0);

[ruiq, 2015/07/29 00:14:17]

Done.

[Mark Seaborn, 2015/07/29 00:31:39]

Won't that fail when running PNaCl apps inside Chrome on ARM?  The code is
currently passing non-zero flags for all architectures when running PNaCl.

   CheckAddressAlignAndOverflow((uint8_t *) guest_addr, size);
   CheckAddressOverflow(data, size);
   CheckAddressOverflow(data, size);
 
   if (stubout_mode)
     return NaClValidationFailedNotImplemented;
 
   CHECK(guest_addr <= std::numeric_limits<uint32_t>::max());
 
   // These checks are redundant with ones done inside the validator. It is done
@@ skipping 99 matching lines @@
   // so is their mix (single instruction update is atomic).
   // We just have to make sure that unintended fallthrough doesn't
   // happen, and we don't change position of guard instructions.
   // Problem is that code is mapped for execution at different address
   // that one we use here, and ARM usually use virtually indexed caches,
   // so we couldn't invalidate correctly anyway.
   return 0;
 }
 
 EXTERN_C_END