| 1 | //===-- asan_premap_shadow.cpp --------------------------------------------===// |
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| 2 | // |
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| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
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| 4 | // See https://llvm.org/LICENSE.txt for license information. |
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| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
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| 6 | // |
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| 7 | //===----------------------------------------------------------------------===// |
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| 8 | // |
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| 9 | // This file is a part of AddressSanitizer, an address sanity checker. |
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| 10 | // |
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| 11 | // Reserve shadow memory with an ifunc resolver. |
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| 12 | //===----------------------------------------------------------------------===// |
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| 13 | |
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| 14 | #include "asan_mapping.h" |
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| 15 | |
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| 16 | #if ASAN_PREMAP_SHADOW |
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| 17 | |
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| 18 | #include "asan_premap_shadow.h" |
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| 19 | #include "sanitizer_common/sanitizer_posix.h" |
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| 20 | |
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| 21 | namespace __asan { |
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| 22 | |
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| 23 | // The code in this file needs to run in an unrelocated binary. It may not |
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| 24 | // access any external symbol, including its own non-hidden globals. |
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| 25 | |
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| 26 | // Conservative upper limit. |
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| 27 | uptr PremapShadowSize() { |
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| 28 | uptr granularity = GetMmapGranularity(); |
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| 29 | return RoundUpTo(GetMaxVirtualAddress() >> ASAN_SHADOW_SCALE, granularity); |
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| 30 | } |
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| 31 | |
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| 32 | // Returns an address aligned to 8 pages, such that one page on the left and |
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| 33 | // PremapShadowSize() bytes on the right of it are mapped r/o. |
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| 34 | uptr PremapShadow() { |
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| 35 | return MapDynamicShadow(PremapShadowSize(), /*mmap_alignment_scale*/ 3, |
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| 36 | /*min_shadow_base_alignment*/ 0, kHighMemEnd); |
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| 37 | } |
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| 38 | |
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| 39 | bool PremapShadowFailed() { |
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| 40 | uptr shadow = reinterpret_cast<uptr>(&__asan_shadow); |
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| 41 | uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow); |
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| 42 | // shadow == resolver is how Android KitKat and older handles ifunc. |
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| 43 | // shadow == 0 just in case. |
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| 44 | if (shadow == 0 || shadow == resolver) |
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| 45 | return true; |
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| 46 | return false; |
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| 47 | } |
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| 48 | } // namespace __asan |
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| 49 | |
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| 50 | extern "C" { |
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| 51 | decltype(__asan_shadow)* __asan_premap_shadow() { |
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| 52 | // The resolver may be called multiple times. Map the shadow just once. |
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| 53 | static uptr premapped_shadow = 0; |
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| 54 | if (!premapped_shadow) premapped_shadow = __asan::PremapShadow(); |
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| 55 | return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow); |
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| 56 | } |
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| 57 | |
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| 58 | // __asan_shadow is a "function" that has the same address as the first byte of |
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| 59 | // the shadow mapping. |
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| 60 | INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow" ))) void |
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| 61 | __asan_shadow(); |
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| 62 | } |
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| 63 | |
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| 64 | #endif // ASAN_PREMAP_SHADOW |
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| 65 | |
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