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-exception 6 // 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_SHADOW 17 18 #include "asan_premap_shadow.h" 19 #include "sanitizer_common/sanitizer_posix.h" 20 21 namespace __asan { 22 23 // The code in this file needs to run in an unrelocated binary. It may not 24 // access any external symbol, including its own non-hidden globals. 25 26 // Conservative upper limit. 27 uptr PremapShadowSize() { 28 uptr granularity = GetMmapGranularity(); 29 return RoundUpTo(GetMaxVirtualAddress() >> SHADOW_SCALE, granularity); 30 } 31 32 // Returns an address aligned to 8 pages, such that one page on the left and 33 // PremapShadowSize() bytes on the right of it are mapped r/o. 34 uptr PremapShadow() { 35 return MapDynamicShadow(PremapShadowSize(), /*mmap_alignment_scale*/ 3, 36 /*min_shadow_base_alignment*/ 0, kHighMemEnd); 37 } 38 39 bool PremapShadowFailed() { 40 uptr shadow = reinterpret_cast<uptr>(&__asan_shadow); 41 uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow); 42 // shadow == resolver is how Android KitKat and older handles ifunc. 43 // shadow == 0 just in case. 44 if (shadow == 0 || shadow == resolver) 45 return true; 46 return false; 47 } 48 } // namespace __asan 49 50 extern "C" { 51 decltype(__asan_shadow)* __asan_premap_shadow() { 52 // The resolver may be called multiple times. Map the shadow just once. 53 static uptr premapped_shadow = 0; 54 if (!premapped_shadow) premapped_shadow = __asan::PremapShadow(); 55 return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow); 56 } 57 58 // __asan_shadow is a "function" that has the same address as the first byte of 59 // the shadow mapping. 60 INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void 61 __asan_shadow(); 62 } 63 64 #endif // ASAN_PREMAP_SHADOW 65