llvm-project

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//===-- asan_premap_shadow.cpp --------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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() >> ASAN_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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  return MapDynamicShadow(PremapShadowSize(), /*mmap_alignment_scale*/ 3,
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                          /*min_shadow_base_alignment*/ 0, kHighMemEnd,
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                          GetMmapGranularity());
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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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