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 uptr granularity = GetMmapGranularity(); 36 uptr alignment = granularity * 8; 37 uptr left_padding = granularity; 38 uptr shadow_size = PremapShadowSize(); 39 uptr map_size = shadow_size + left_padding + alignment; 40 41 uptr map_start = (uptr)MmapNoAccess(map_size); 42 CHECK_NE(map_start, ~(uptr)0); 43 44 uptr shadow_start = RoundUpTo(map_start + left_padding, alignment); 45 uptr shadow_end = shadow_start + shadow_size; 46 internal_munmap(reinterpret_cast<void *>(map_start), 47 shadow_start - left_padding - map_start); 48 internal_munmap(reinterpret_cast<void *>(shadow_end), 49 map_start + map_size - shadow_end); 50 return shadow_start; 51 } 52 53 bool PremapShadowFailed() { 54 uptr shadow = reinterpret_cast<uptr>(&__asan_shadow); 55 uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow); 56 // shadow == resolver is how Android KitKat and older handles ifunc. 57 // shadow == 0 just in case. 58 if (shadow == 0 || shadow == resolver) 59 return true; 60 return false; 61 } 62 } // namespace __asan 63 64 extern "C" { 65 decltype(__asan_shadow)* __asan_premap_shadow() { 66 // The resolver may be called multiple times. Map the shadow just once. 67 static uptr premapped_shadow = 0; 68 if (!premapped_shadow) premapped_shadow = __asan::PremapShadow(); 69 return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow); 70 } 71 72 // __asan_shadow is a "function" that has the same address as the first byte of 73 // the shadow mapping. 74 INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void 75 __asan_shadow(); 76 } 77 78 #endif // ASAN_PREMAP_SHADOW 79