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() >> ASAN_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 GetMmapGranularity()); 38 } 39 40 bool 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 __asan 50 51 extern "C" { 52 decltype(__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 of 60 // the shadow mapping. 61 INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void 62 __asan_shadow(); 63 } 64 65 #endif // ASAN_PREMAP_SHADOW 66