88 lines
2.4 KiB
C++
88 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 "platform/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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public:
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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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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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set_protection(PROT_READ);
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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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set_protection(PROT_READ | PROT_WRITE);
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mutator(&contents.value);
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set_protection(PROT_READ);
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}
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private:
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WriteProtectedContents<T> contents;
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void set_protection(int prot) {
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auto addr = &contents;
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#if __has_feature(hwaddress_sanitizer)
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// The mprotect system call does not currently untag pointers, so do it
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// ourselves.
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addr = untag_address(addr);
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#endif
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if (mprotect(reinterpret_cast<void*>(addr), PAGE_SIZE, prot) == -1) {
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async_safe_fatal("WriteProtected mprotect %x failed: %s", prot, strerror(errno));
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}
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}
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};
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