blob: d94b0770cec113a1ee110e798218635f83964b06 [file] [log] [blame]
// Copyright 2021 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.
#include "v8_platform_page_allocator.h"
#include "base/allocator/partition_allocator/address_space_randomization.h"
#include "base/allocator/partition_allocator/page_allocator_constants.h"
#include "base/allocator/partition_allocator/random.h"
#include "base/check_op.h"
#include "base/cpu.h"
#include "build/build_config.h"
namespace {
// Maps the v8 page permissions into a page configuration from base.
base::PageAccessibilityConfiguration GetPageConfig(
v8::PageAllocator::Permission permission) {
switch (permission) {
case v8::PageAllocator::Permission::kRead:
return base::PageRead;
case v8::PageAllocator::Permission::kReadWrite:
return base::PageReadWrite;
case v8::PageAllocator::Permission::kReadWriteExecute:
// at the moment bti-protection is not enabled for this path since some
// projects may still be using non-bti compliant code.
return base::PageReadWriteExecute;
case v8::PageAllocator::Permission::kReadExecute:
return base::CPU::GetInstanceNoAllocation().has_bti()
? base::PageReadExecuteProtected
: base::PageReadExecute;
return base::PageReadExecute;
case v8::PageAllocator::Permission::kNoAccessWillJitLater:
// We could use this information to conditionally set the MAP_JIT flag
// on Mac-arm64; however this permissions value is intended to be a
// short-term solution, so we continue to set MAP_JIT for all V8 pages
// for now.
return base::PageInaccessible;
DCHECK_EQ(v8::PageAllocator::Permission::kNoAccess, permission);
return base::PageInaccessible;
} // namespace
namespace gin {
PageAllocator::~PageAllocator() = default;
size_t PageAllocator::AllocatePageSize() {
return base::PageAllocationGranularity();
size_t PageAllocator::CommitPageSize() {
return base::SystemPageSize();
void PageAllocator::SetRandomMmapSeed(int64_t seed) {
void* PageAllocator::GetRandomMmapAddr() {
return base::GetRandomPageBase();
void* PageAllocator::AllocatePages(void* address,
size_t length,
size_t alignment,
v8::PageAllocator::Permission permissions) {
base::PageAccessibilityConfiguration config = GetPageConfig(permissions);
return base::AllocPages(address, length, alignment, config,
bool PageAllocator::FreePages(void* address, size_t length) {
base::FreePages(address, length);
return true;
bool PageAllocator::ReleasePages(void* address,
size_t length,
size_t new_length) {
DCHECK_LT(new_length, length);
uint8_t* release_base = reinterpret_cast<uint8_t*>(address) + new_length;
size_t release_size = length - new_length;
// On POSIX, we can unmap the trailing pages.
base::FreePages(release_base, release_size);
// On Windows, we can only de-commit the trailing pages. FreePages() will
// still free all pages in the region including the released tail, so it's
// safe to just decommit the tail.
base::DecommitSystemPages(release_base, release_size,
#error Unsupported platform
return true;
bool PageAllocator::SetPermissions(void* address,
size_t length,
Permission permissions) {
// If V8 sets permissions to none, we can discard the memory.
if (permissions == v8::PageAllocator::Permission::kNoAccess) {
// Use PageKeepPermissionsIfPossible as an optimization, to avoid perf
// regression (see for details). This may cause the
// memory region to still be accessible on certain platforms, but at least
// the physical pages will be discarded.
base::DecommitSystemPages(address, length,
return true;
} else {
return base::TrySetSystemPagesAccess(address, length,
bool PageAllocator::DiscardSystemPages(void* address, size_t size) {
base::DiscardSystemPages(address, size);
return true;
bool PageAllocator::DecommitPages(void* address, size_t size) {
// V8 expects the pages to be inaccessible and zero-initialized upon next
// access.
base::DecommitAndZeroSystemPages(address, size);
return true;
base::PageAccessibilityConfiguration PageAllocator::GetPageConfigForTesting(
v8::PageAllocator::Permission permission) {
return GetPageConfig(permission);
} // namespace gin