5e62b34c0d
Use <android-base/macros.h> instead where possible, and move the bionic macros out of the way of the libbase ones. Yes, there are folks who manage to end up with both included at once (thanks OpenGL!), and cleaning that up doesn't seem nearly as practical as just making this change. Bug: N/A Test: builds Change-Id: I23fc544f39d5addf81dc61471771a5438778895b
83 lines
2.4 KiB
C++
83 lines
2.4 KiB
C++
/*
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* Copyright (C) 2015 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <errno.h>
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#include <string.h>
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#include <sys/cdefs.h>
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#include <sys/mman.h>
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#include <sys/user.h>
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#include <async_safe/log.h>
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#include "private/bionic_macros.h"
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template <typename T>
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union WriteProtectedContents {
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T value;
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char padding[PAGE_SIZE];
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WriteProtectedContents() = default;
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BIONIC_DISALLOW_COPY_AND_ASSIGN(WriteProtectedContents);
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} __attribute__((aligned(PAGE_SIZE)));
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// Write protected wrapper class that aligns its contents to a page boundary,
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// and sets the memory protection to be non-writable, except when being modified
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// explicitly.
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template <typename T>
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class WriteProtected {
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static_assert(sizeof(T) < PAGE_SIZE,
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"WriteProtected only supports contents up to PAGE_SIZE");
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static_assert(__is_pod(T), "WriteProtected only supports POD contents");
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WriteProtectedContents<T> contents;
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public:
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WriteProtected() = default;
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BIONIC_DISALLOW_COPY_AND_ASSIGN(WriteProtected);
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void initialize() {
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// Not strictly necessary, but this will hopefully segfault if we initialize
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// multiple times by accident.
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memset(&contents, 0, sizeof(contents));
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if (mprotect(&contents, PAGE_SIZE, PROT_READ)) {
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async_safe_fatal("failed to make WriteProtected nonwritable in initialize");
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}
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}
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const T* operator->() {
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return &contents.value;
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}
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const T& operator*() {
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return contents.value;
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}
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template <typename Mutator>
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void mutate(Mutator mutator) {
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if (mprotect(&contents, PAGE_SIZE, PROT_READ | PROT_WRITE) != 0) {
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async_safe_fatal("failed to make WriteProtected writable in mutate: %s",
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strerror(errno));
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}
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mutator(&contents.value);
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if (mprotect(&contents, PAGE_SIZE, PROT_READ) != 0) {
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async_safe_fatal("failed to make WriteProtected nonwritable in mutate: %s",
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strerror(errno));
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}
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}
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};
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