Add UMA for testing whether device supports memory mapping APK files with executable permissions.

base/android/linker/linker_jni.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This is the Android-specific Chromium linker, a tiny shared library
 // implementing a custom dynamic linker that can be used to load the
 // real Chromium libraries (e.g. libcontentshell.so).
 
 // The main point of this linker is to be able to share the RELRO
 // section of libcontentshell.so (or equivalent) between the browser and
 // renderer process.
 
 // This source code *cannot* depend on anything from base/ or the C++
 // STL, to keep the final library small, and avoid ugly dependency issues.
 
 #include <android/log.h>
 #include <crazy_linker.h>
+#include <errno.h>
+#include <fcntl.h>
 #include <jni.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <unistd.h>
 
 // Set this to 1 to enable debug traces to the Android log.
 // Note that LOG() from "base/logging.h" cannot be used, since it is
 // in base/ which hasn't been loaded yet.
 #define DEBUG 0
 
 #define TAG "chromium_android_linker"
@@ skipping 538 matching lines @@
       mmap(NULL, bytes, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
   if (address == MAP_FAILED) {
     LOG_INFO("%s: Random base load address not determinable\n", __FUNCTION__);
     return 0;
   }
   munmap(address, bytes);
   LOG_INFO("%s: Random base load address is %p\n", __FUNCTION__, address);
   return static_cast<jlong>(reinterpret_cast<uintptr_t>(address));
 }
 
+// Check whether the device supports memory mapping APK files with executable
+// permissions.
+//
+// |env| is the current JNI environment handle and is ignored here.

[rmcilroy, 2014/10/10 16:26:08]

not ignored - used for string conversion

[petrcermak, 2014/10/10 17:13:24]

Done.

+// |clazz| is the static class handle for org.chromium.base.Linker,
+// and is ignored here.

[rmcilroy, 2014/10/10 16:26:08]

nit - I would just write "|class| is the static class handle which is not used
here."

[petrcermak, 2014/10/10 17:13:24]

Done.

+// |apkfile_name| is the filename of the APK.
+// Returns true if supported.
+jboolean CheckApkMemoryMappingSupport(JNIEnv* env, jclass clazz,
+                                      jstring apkfile_name) {
+  String apkfile_name_str(env, apkfile_name);
+  const char* apkfile_name_c_str = apkfile_name_str.c_str();
+
+  int fd = TEMP_FAILURE_RETRY(open(apkfile_name_c_str, O_RDONLY));

[rmcilroy, 2014/10/10 16:26:08]

I would avoid the TEMP_FAILURE_RETRY - it's not super critical that this
succeeds and I'm worried that we might end up in a retry loop here if glibc
decides it needs to keep retrying.

[petrcermak, 2014/10/10 17:13:24]

Done.

+  if (fd == -1) {
+    LOG_ERROR("%s: Failed to open %s\n", __FUNCTION__, apkfile_name_c_str);
+    return 0;
+  }
+
+  LOG_INFO("%s: Memory mapping the first page of %s\n", __FUNCTION__,
+           apkfile_name_c_str);
+  void* address = mmap(NULL, PAGE_SIZE, PROT_EXEC, MAP_PRIVATE, fd, 0);
+
+  jboolean success;
+  if (address == MAP_FAILED) {
+    success = 0;

[rmcilroy, 2014/10/10 16:26:08]

/s/0/false (and true for '1' below)

[petrcermak, 2014/10/10 17:13:24]

Done.

+  } else {
+    success = 1;
+    munmap(address, PAGE_SIZE);
+  }
+
+  TEMP_FAILURE_RETRY(close(fd));

[rmcilroy, 2014/10/10 16:26:08]

ditto

[petrcermak, 2014/10/10 17:13:24]

Done.

+
+  LOG_INFO("  %ssupported\n", success ? "" : "NOT ");
+  return success;
+
+}
+
 const JNINativeMethod kNativeMethods[] = {
     {"nativeLoadLibrary",
      "("
      "Ljava/lang/String;"
      "J"
      "Lorg/chromium/base/library_loader/Linker$LibInfo;"
      ")"
      "Z",
      reinterpret_cast<void*>(&LoadLibrary)},
     {"nativeLoadLibraryInZipFile",
@@ skipping 29 matching lines @@
     {"nativeCanUseSharedRelro",
      "("
      ")"
      "Z",
      reinterpret_cast<void*>(&CanUseSharedRelro)},
     {"nativeGetRandomBaseLoadAddress",
      "("
      "J"
      ")"
      "J",
-     reinterpret_cast<void*>(&GetRandomBaseLoadAddress)}, };
+     reinterpret_cast<void*>(&GetRandomBaseLoadAddress)},
+     {"nativeCheckApkMemoryMappingSupport",
+      "("
+      "Ljava/lang/String;"
+      ")"
+      "Z",
+      reinterpret_cast<void*>(&CheckApkMemoryMappingSupport)}, };
 
 }  // namespace
 
 // JNI_OnLoad() hook called when the linker library is loaded through
 // the regular System.LoadLibrary) API. This shall save the Java VM
 // handle and initialize LibInfo fields.
 jint JNI_OnLoad(JavaVM* vm, void* reserved) {
   LOG_INFO("%s: Entering", __FUNCTION__);
   // Get new JNIEnv
   JNIEnv* env;
@@ skipping 30 matching lines @@
   crazy_context_t* context = GetCrazyContext();
   crazy_context_set_java_vm(context, vm, JNI_VERSION_1_4);
 
   // Register the function that the crazy linker can call to post code
   // for later execution.
   crazy_context_set_callback_poster(context, &PostForLaterExecution, NULL);
 
   LOG_INFO("%s: Done", __FUNCTION__);
   return JNI_VERSION_1_4;
 }