//===-- asan_premap_shadow.cpp --------------------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file is a part of AddressSanitizer, an address sanity checker. // // Reserve shadow memory with an ifunc resolver. //===----------------------------------------------------------------------===// #include "asan_mapping.h" #if ASAN_PREMAP_SHADOW #include "asan_premap_shadow.h" #include "sanitizer_common/sanitizer_posix.h" namespace __asan { // The code in this file needs to run in an unrelocated binary. It may not // access any external symbol, including its own non-hidden globals. // Conservative upper limit. uptr PremapShadowSize() { uptr granularity = GetMmapGranularity(); return RoundUpTo(GetMaxVirtualAddress() >> SHADOW_SCALE, granularity); } // Returns an address aligned to 8 pages, such that one page on the left and // PremapShadowSize() bytes on the right of it are mapped r/o. uptr PremapShadow() { uptr granularity = GetMmapGranularity(); uptr alignment = granularity * 8; uptr left_padding = granularity; uptr shadow_size = PremapShadowSize(); uptr map_size = shadow_size + left_padding + alignment; uptr map_start = (uptr)MmapNoAccess(map_size); CHECK_NE(map_start, ~(uptr)0); uptr shadow_start = RoundUpTo(map_start + left_padding, alignment); uptr shadow_end = shadow_start + shadow_size; internal_munmap(reinterpret_cast<void *>(map_start), shadow_start - left_padding - map_start); internal_munmap(reinterpret_cast<void *>(shadow_end), map_start + map_size - shadow_end); return shadow_start; } bool PremapShadowFailed() { uptr shadow = reinterpret_cast<uptr>(&__asan_shadow); uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow); // shadow == resolver is how Android KitKat and older handles ifunc. // shadow == 0 just in case. if (shadow == 0 || shadow == resolver) return true; return false; } } // namespace __asan extern "C" { decltype(__asan_shadow)* __asan_premap_shadow() { // The resolver may be called multiple times. Map the shadow just once. static uptr premapped_shadow = 0; if (!premapped_shadow) premapped_shadow = __asan::PremapShadow(); return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow); } // __asan_shadow is a "function" that has the same address as the first byte of // the shadow mapping. INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void __asan_shadow(); } #endif // ASAN_PREMAP_SHADOW |