66 lines · cpp
1//===-- asan_premap_shadow.cpp --------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This file is a part of AddressSanitizer, an address sanity checker.10//11// Reserve shadow memory with an ifunc resolver.12//===----------------------------------------------------------------------===//13 14#include "asan_mapping.h"15 16#if ASAN_PREMAP_SHADOW17 18#include "asan_premap_shadow.h"19#include "sanitizer_common/sanitizer_posix.h"20 21namespace __asan {22 23// The code in this file needs to run in an unrelocated binary. It may not24// access any external symbol, including its own non-hidden globals.25 26// Conservative upper limit.27uptr PremapShadowSize() {28 uptr granularity = GetMmapGranularity();29 return RoundUpTo(GetMaxVirtualAddress() >> ASAN_SHADOW_SCALE, granularity);30}31 32// Returns an address aligned to 8 pages, such that one page on the left and33// PremapShadowSize() bytes on the right of it are mapped r/o.34uptr PremapShadow() {35 return MapDynamicShadow(PremapShadowSize(), /*mmap_alignment_scale*/ 3,36 /*min_shadow_base_alignment*/ 0, kHighMemEnd,37 GetMmapGranularity());38}39 40bool PremapShadowFailed() {41 uptr shadow = reinterpret_cast<uptr>(&__asan_shadow);42 uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow);43 // shadow == resolver is how Android KitKat and older handles ifunc.44 // shadow == 0 just in case.45 if (shadow == 0 || shadow == resolver)46 return true;47 return false;48}49} // namespace __asan50 51extern "C" {52decltype(__asan_shadow)* __asan_premap_shadow() {53 // The resolver may be called multiple times. Map the shadow just once.54 static uptr premapped_shadow = 0;55 if (!premapped_shadow) premapped_shadow = __asan::PremapShadow();56 return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow);57}58 59// __asan_shadow is a "function" that has the same address as the first byte of60// the shadow mapping.61INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void62__asan_shadow();63}64 65#endif // ASAN_PREMAP_SHADOW66