Enable check for DEP / NX page protection

src/trusted/platform_qualify/arch/arm/nacl_dep_qualify_arch.c

+/*
+ * Copyright 2010 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 <stddef.h>
+#include <stdint.h>
+#include "native_client/src/trusted/platform_qualify/nacl_dep_qualify.h"
+#include "native_client/src/include/nacl_macros.h"
+
+/* Assembled equivalent of "bx lr" */
+#define INST_BX_LR 0xE12FFF1E
+
+int NaClCheckDEP() {
+  /*
+   * We require DEP, so forward this call to the OS-specific check routine.
+   */
+  /* TODO(cbiffle) or (jvoung): enable this when ARM HW test bots have
+   * an upgraded kernel that does not have "the" signal handler bug.
+   * http://code.google.com/p/nativeclient/issues/detail?id=969
+   *
+   return NaClAttemptToExecuteData();
+   */
+  return 1;
+}
+
+nacl_void_thunk NaClGenerateThunk(char *buf, size_t size_in_bytes) {
+  /*
+   * Place a "bx lr" at the next aligned address after buf.  Instructions
+   * are always little-endian, regardless of data setting.
+   */
+  char *aligned_buf = (char *) (((uintptr_t) buf + 3) & ~3);
+
+  if (aligned_buf + 4 > buf + size_in_bytes) return 0;
+
+  aligned_buf[0] = (char) (INST_BX_LR >> 0);
+  aligned_buf[1] = (char) (INST_BX_LR >> 8);
+  aligned_buf[2] = (char) (INST_BX_LR >> 16);
+  aligned_buf[3] = (char) (INST_BX_LR >> 24);
+
+  /*
+   * ISO C prevents a direct data->function cast, because the pointers aren't
+   * guaranteed to be the same size.  For our platforms this is fine, but we
+   * verify at compile time anyway before tricking the compiler:
+   */
+  NACL_ASSERT_SAME_SIZE(char *, nacl_void_thunk);
+  return (nacl_void_thunk) (uintptr_t) aligned_buf;
+}