1 //===-- asan_premap_shadow.cc ---------------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file is a part of AddressSanitizer, an address sanity checker.
12 // Reserve shadow memory with an ifunc resolver.
13 //===----------------------------------------------------------------------===//
15 #include "asan_mapping.h"
17 #if ASAN_PREMAP_SHADOW
19 #include "asan_premap_shadow.h"
20 #include "sanitizer_common/sanitizer_posix.h"
24 // The code in this file needs to run in an unrelocated binary. It may not
25 // access any external symbol, including its own non-hidden globals.
27 // Conservative upper limit.
28 uptr PremapShadowSize() {
29 uptr granularity = GetMmapGranularity();
30 return RoundUpTo(GetMaxVirtualAddress() >> SHADOW_SCALE, granularity);
33 // Returns an address aligned to 8 pages, such that one page on the left and
34 // PremapShadowSize() bytes on the right of it are mapped r/o.
36 uptr granularity = GetMmapGranularity();
37 uptr alignment = granularity * 8;
38 uptr left_padding = granularity;
39 uptr shadow_size = PremapShadowSize();
40 uptr map_size = shadow_size + left_padding + alignment;
42 uptr map_start = (uptr)MmapNoAccess(map_size);
43 CHECK_NE(map_start, ~(uptr)0);
45 uptr shadow_start = RoundUpTo(map_start + left_padding, alignment);
46 uptr shadow_end = shadow_start + shadow_size;
47 internal_munmap(reinterpret_cast<void *>(map_start),
48 shadow_start - left_padding - map_start);
49 internal_munmap(reinterpret_cast<void *>(shadow_end),
50 map_start + map_size - shadow_end);
54 bool PremapShadowFailed() {
55 uptr shadow = reinterpret_cast<uptr>(&__asan_shadow);
56 uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow);
57 // shadow == resolver is how Android KitKat and older handles ifunc.
58 // shadow == 0 just in case.
59 if (shadow == 0 || shadow == resolver)
66 decltype(__asan_shadow)* __asan_premap_shadow() {
67 // The resolver may be called multiple times. Map the shadow just once.
68 static uptr premapped_shadow = 0;
69 if (!premapped_shadow) premapped_shadow = __asan::PremapShadow();
70 return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow);
73 // __asan_shadow is a "function" that has the same address as the first byte of
74 // the shadow mapping.
75 INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void
79 #endif // ASAN_PREMAP_SHADOW