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//===-- asan_premap_shadow.cc ---------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file is a part of AddressSanitizer, an address sanity checker.
//
// Reserve shadow memory with an ifunc resolver.
//===----------------------------------------------------------------------===//
#include "asan_mapping.h"
#if ASAN_PREMAP_SHADOW
#include "asan_premap_shadow.h"
#include "sanitizer_common/sanitizer_posix.h"
namespace __asan {
// The code in this file needs to run in an unrelocated binary. It may not
// access any external symbol, including its own non-hidden globals.
// Conservative upper limit.
uptr PremapShadowSize() {
uptr granularity = GetMmapGranularity();
return RoundUpTo(GetMaxVirtualAddress() >> SHADOW_SCALE, granularity);
}
// Returns an address aligned to 8 pages, such that one page on the left and
// PremapShadowSize() bytes on the right of it are mapped r/o.
uptr PremapShadow() {
uptr granularity = GetMmapGranularity();
uptr alignment = granularity * 8;
uptr left_padding = granularity;
uptr shadow_size = PremapShadowSize();
uptr map_size = shadow_size + left_padding + alignment;
uptr map_start = (uptr)MmapNoAccess(map_size);
CHECK_NE(map_start, ~(uptr)0);
uptr shadow_start = RoundUpTo(map_start + left_padding, alignment);
uptr shadow_end = shadow_start + shadow_size;
internal_munmap(reinterpret_cast<void *>(map_start),
shadow_start - left_padding - map_start);
internal_munmap(reinterpret_cast<void *>(shadow_end),
map_start + map_size - shadow_end);
return shadow_start;
}
bool PremapShadowFailed() {
uptr shadow = reinterpret_cast<uptr>(&__asan_shadow);
uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow);
// shadow == resolver is how Android KitKat and older handles ifunc.
// shadow == 0 just in case.
if (shadow == 0 || shadow == resolver)
return true;
return false;
}
} // namespace __asan
extern "C" {
decltype(__asan_shadow)* __asan_premap_shadow() {
// The resolver may be called multiple times. Map the shadow just once.
static uptr premapped_shadow = 0;
if (!premapped_shadow) premapped_shadow = __asan::PremapShadow();
return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow);
}
// __asan_shadow is a "function" that has the same address as the first byte of
// the shadow mapping.
INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void
__asan_shadow();
}
#endif // ASAN_PREMAP_SHADOW
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