8401230be6
The maximum page size Android supports now is 16384, and Art only supports 16kB, so we can save a bit of space. Bug: 332556665 Test: N/A Change-Id: I23df607bcc5cf9e96d7b6a66169413cd1a883f7e
96 lines
2.9 KiB
C++
96 lines
2.9 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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#include "platform/bionic/page.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[max_android_page_size()];
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WriteProtectedContents() = default;
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BIONIC_DISALLOW_COPY_AND_ASSIGN(WriteProtectedContents);
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} __attribute__((aligned(max_android_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) < max_android_page_size(),
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"WriteProtected only supports contents up to max_android_page_size()");
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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_addr(), 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_addr()->value;
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}
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const T& operator*() {
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return contents_addr()->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_addr()->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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WriteProtectedContents<T>* contents_addr() {
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auto addr = &contents;
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// Hide the fact that we're returning the address of contents from the compiler.
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// Otherwise it may generate code assuming alignment of 64KB even though the
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// variable is only guaranteed to have 4KB alignment.
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__asm__ __volatile__("" : "+r"(addr));
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return addr;
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}
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void set_protection(int prot) {
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auto addr = contents_addr();
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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), max_android_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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