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
21namespace __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.
27uptr PremapShadowSize() {
28 uptr granularity = GetMmapGranularity();
29 return RoundUpTo(GetMaxVirtualAddress() >> ASAN_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.
34uptr PremapShadow() {
35 return MapDynamicShadow(PremapShadowSize(), /*mmap_alignment_scale*/ 3,
36 /*min_shadow_base_alignment*/ 0, kHighMemEnd,
37 GetMmapGranularity());
38}
39
40bool PremapShadowFailed() {
41 uptr shadow = reinterpret_cast<uptr>(&__asan_shadow);
42 uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow);
43 // shadow == resolver is how Android KitKat and older handles ifunc.
44 // shadow == 0 just in case.
45 if (shadow == 0 || shadow == resolver)
46 return true;
47 return false;
48}
49} // namespace __asan
50
51extern "C" {
52decltype(__asan_shadow)* __asan_premap_shadow() {
53 // The resolver may be called multiple times. Map the shadow just once.
54 static uptr premapped_shadow = 0;
55 if (!premapped_shadow) premapped_shadow = __asan::PremapShadow();
56 return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow);
57}
58
59// __asan_shadow is a "function" that has the same address as the first byte of
60// the shadow mapping.
61INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void
62__asan_shadow();
63}
64
65#endif // ASAN_PREMAP_SHADOW
66