[mojo] refactor shmem utilities to hide implementation details.

Code should just use the //base abstractions directly. Update
the API to just expose a way to install the Mojo hooks.

Fixed: 876525
Change-Id: Ic90adb8eae9ee065977e81c7ec7ccf330a12c93b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2102635
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#755187}

base/memory/read_only_shared_memory_region.h

@@ -32,12 +32,6 @@ class BASE_EXPORT ReadOnlySharedMemoryRegion {
   // This means that the caller's process is the only process that can modify
   // the region content. If you need to pass write access to another process,
   // consider using WritableSharedMemoryRegion or UnsafeSharedMemoryRegion.
-  //
-  // This call will fail if the process does not have sufficient permissions to
-  // create a shared memory region itself. See
-  // mojo::CreateReadOnlySharedMemoryRegion in
-  // mojo/public/cpp/base/shared_memory_utils.h for creating a shared memory
-  // region from a an unprivileged process where a broker must be used.
   static MappedReadOnlyRegion Create(size_t size);
   using CreateFunction = decltype(Create);
 

base/memory/shared_memory_hooks.h

@@ -16,10 +16,11 @@ struct MainFunctionParams;
 }  // namespace content
 int CloudPrintServiceProcessMain(const content::MainFunctionParams& parameters);
 
-namespace service_manager {
-struct MainParams;
-int Main(const MainParams&);
-}  // namespace service_manager
+namespace mojo {
+
+class SharedMemoryUtils;
+
+}  // namespace mojo
 
 namespace base {
 
@@ -31,7 +32,7 @@ class SharedMemoryHooks {
   friend class SharedMemoryHooksTest;
   friend int ::CloudPrintServiceProcessMain(
       const content::MainFunctionParams& parameters);
-  friend int service_manager::Main(const service_manager::MainParams&);
+  friend mojo::SharedMemoryUtils;
 
   // Allows shared memory region creation to be hooked. Useful for sandboxed
   // processes that are restricted from invoking the platform APIs directly.

base/memory/unsafe_shared_memory_region.h

@@ -31,12 +31,6 @@ class BASE_EXPORT UnsafeSharedMemoryRegion {
   using MappingType = WritableSharedMemoryMapping;
   // Creates a new UnsafeSharedMemoryRegion instance of a given size that can be
   // used for mapping writable shared memory into the virtual address space.
-  //
-  // This call will fail if the process does not have sufficient permissions to
-  // create a shared memory region itself. See
-  // mojo::CreateUnsafeSharedMemoryRegion in
-  // mojo/public/cpp/base/shared_memory_utils.h for creating a shared memory
-  // region from a an unprivileged process where a broker must be used.
   static UnsafeSharedMemoryRegion Create(size_t size);
   using CreateFunction = decltype(Create);
 

base/memory/writable_shared_memory_region.h

@@ -33,12 +33,6 @@ class BASE_EXPORT WritableSharedMemoryRegion {
   // Creates a new WritableSharedMemoryRegion instance of a given
   // size that can be used for mapping writable shared memory into the virtual
   // address space.
-  //
-  // This call will fail if the process does not have sufficient permissions to
-  // create a shared memory region itself. See
-  // mojo::CreateWritableSharedMemoryRegion in
-  // mojo/public/cpp/base/shared_memory_utils.h for creating a shared memory
-  // region from a an unprivileged process where a broker must be used.
   static WritableSharedMemoryRegion Create(size_t size);
   using CreateFunction = decltype(Create);
 

mojo/public/cpp/base/shared_memory_utils.cc

@@ -4,12 +4,27 @@
 
 #include "mojo/public/cpp/base/shared_memory_utils.h"
 
+#include "base/memory/read_only_shared_memory_region.h"
+#include "base/memory/shared_memory_hooks.h"
 #include "base/memory/shared_memory_mapping.h"
+#include "base/memory/unsafe_shared_memory_region.h"
+#include "base/memory/writable_shared_memory_region.h"
 #include "mojo/public/cpp/system/buffer.h"
 #include "mojo/public/cpp/system/platform_handle.h"
 
 namespace mojo {
 
+namespace {
+
+base::WritableSharedMemoryRegion CreateWritableSharedMemoryRegion(size_t size) {
+  mojo::ScopedSharedBufferHandle handle =
+      mojo::SharedBufferHandle::Create(size);
+  if (!handle.is_valid())
+    return base::WritableSharedMemoryRegion();
+
+  return mojo::UnwrapWritableSharedMemoryRegion(std::move(handle));
+}
+
 base::MappedReadOnlyRegion CreateReadOnlySharedMemoryRegion(size_t size) {
   auto writable_region = CreateWritableSharedMemoryRegion(size);
   if (!writable_region.IsValid())
@@ -30,13 +45,12 @@ base::UnsafeSharedMemoryRegion CreateUnsafeSharedMemoryRegion(size_t size) {
       std::move(writable_region));
 }
 
-base::WritableSharedMemoryRegion CreateWritableSharedMemoryRegion(size_t size) {
-  mojo::ScopedSharedBufferHandle handle =
-      mojo::SharedBufferHandle::Create(size);
-  if (!handle.is_valid())
-    return base::WritableSharedMemoryRegion();
+}  // namespace
 
-  return mojo::UnwrapWritableSharedMemoryRegion(std::move(handle));
+void SharedMemoryUtils::InstallBaseHooks() {
+  base::SharedMemoryHooks::SetCreateHooks(&CreateReadOnlySharedMemoryRegion,
+                                          &CreateUnsafeSharedMemoryRegion,
+                                          &CreateWritableSharedMemoryRegion);
 }
 
 }  // namespace mojo

mojo/public/cpp/base/shared_memory_utils.h

@@ -6,25 +6,13 @@
 #define MOJO_PUBLIC_CPP_BASE_SHARED_MEMORY_UTILS_H_
 
 #include "base/component_export.h"
-#include "base/memory/read_only_shared_memory_region.h"
-#include "base/memory/unsafe_shared_memory_region.h"
-#include "base/memory/writable_shared_memory_region.h"
 
 namespace mojo {
 
-// These creation methods are parallel to the base::*SharedMemoryRegion::Create
-// methods. These methods should be used instead of the base:: ones to create
-// shared memory in an unprivileged context, in which case a broker in a
-// privileged process will be used to create the region.
-//
-// IsValid() should be checked on the return value of the following methods to
-// determine if the creation was successful.
-COMPONENT_EXPORT(MOJO_BASE)
-base::MappedReadOnlyRegion CreateReadOnlySharedMemoryRegion(size_t size);
-COMPONENT_EXPORT(MOJO_BASE)
-base::UnsafeSharedMemoryRegion CreateUnsafeSharedMemoryRegion(size_t size);
-COMPONENT_EXPORT(MOJO_BASE)
-base::WritableSharedMemoryRegion CreateWritableSharedMemoryRegion(size_t size);
+class SharedMemoryUtils {
+ public:
+  COMPONENT_EXPORT(MOJO_BASE) static void InstallBaseHooks();
+};
 
 }  // namespace mojo
 

services/service_manager/embedder/main.cc

@@ -401,10 +401,7 @@ int Main(const MainParams& params) {
       DCHECK(!mojo_config.is_broker_process);
       // Otherwise, this is a sandboxed process that will need brokering to
       // allocate shared memory.
-      base::SharedMemoryHooks::SetCreateHooks(
-          &mojo::CreateReadOnlySharedMemoryRegion,
-          &mojo::CreateUnsafeSharedMemoryRegion,
-          &mojo::CreateWritableSharedMemoryRegion);
+      mojo::SharedMemoryUtils::InstallBaseHooks();
     }
 #endif  // !defined(OS_MACOSX) && !defined(OS_NACL_SFI) && !defined(OS_FUCHSIA)