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