libsanitizer/asan/asan_poisoning.cc

   1 //===-- asan_poisoning.cc -------------------------------------------------===//
   2 //
   3 // This file is distributed under the University of Illinois Open Source
   4 // License. See LICENSE.TXT for details.
   5 //
   6 //===----------------------------------------------------------------------===//
   7 //
   8 // This file is a part of AddressSanitizer, an address sanity checker.
   9 //
  10 // Shadow memory poisoning by ASan RTL and by user application.
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "asan_interceptors.h"
  14 #include "asan_internal.h"
  15 #include "asan_mapping.h"
  16 #include "sanitizer_common/sanitizer_libc.h"
  17
  18 namespace __asan {
  19
  20 void PoisonShadow(uptr addr, uptr size, u8 value) {
  21   if (!flags()->poison_heap) return;
  22   CHECK(AddrIsAlignedByGranularity(addr));
  23   CHECK(AddrIsAlignedByGranularity(addr + size));
  24   uptr shadow_beg = MemToShadow(addr);
  25   uptr shadow_end = MemToShadow(addr + size - SHADOW_GRANULARITY) + 1;
  26   CHECK(REAL(memset) != 0);
  27   REAL(memset)((void*)shadow_beg, value, shadow_end - shadow_beg);
  28 }
  29
  30 void PoisonShadowPartialRightRedzone(uptr addr,
  31                                      uptr size,
  32                                      uptr redzone_size,
  33                                      u8 value) {
  34   if (!flags()->poison_heap) return;
  35   CHECK(AddrIsAlignedByGranularity(addr));
  36   u8 *shadow = (u8*)MemToShadow(addr);
  37   for (uptr i = 0; i < redzone_size;
  38        i += SHADOW_GRANULARITY, shadow++) {
  39     if (i + SHADOW_GRANULARITY <= size) {
  40       *shadow = 0;  // fully addressable
  41     } else if (i >= size) {
  42       *shadow = (SHADOW_GRANULARITY == 128) ? 0xff : value;  // unaddressable
  43     } else {
  44       *shadow = size - i;  // first size-i bytes are addressable
  45     }
  46   }
  47 }
  48
  49
  50 struct ShadowSegmentEndpoint {
  51   u8 *chunk;
  52   s8 offset;  // in [0, SHADOW_GRANULARITY)
  53   s8 value;  // = *chunk;
  54
  55   explicit ShadowSegmentEndpoint(uptr address) {
  56     chunk = (u8*)MemToShadow(address);
  57     offset = address & (SHADOW_GRANULARITY - 1);
  58     value = *chunk;
  59   }
  60 };
  61
  62 }  // namespace __asan
  63
  64 // ---------------------- Interface ---------------- {{{1
  65 using namespace __asan;  // NOLINT
  66
  67 // Current implementation of __asan_(un)poison_memory_region doesn't check
  68 // that user program (un)poisons the memory it owns. It poisons memory
  69 // conservatively, and unpoisons progressively to make sure asan shadow
  70 // mapping invariant is preserved (see detailed mapping description here:
  71 // http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm).
  72 //
  73 // * if user asks to poison region [left, right), the program poisons
  74 // at least [left, AlignDown(right)).
  75 // * if user asks to unpoison region [left, right), the program unpoisons
  76 // at most [AlignDown(left), right).
  77 void __asan_poison_memory_region(void const volatile *addr, uptr size) {
  78   if (!flags()->allow_user_poisoning || size == 0) return;
  79   uptr beg_addr = (uptr)addr;
  80   uptr end_addr = beg_addr + size;
  81   if (flags()->verbosity >= 1) {
  82     Printf("Trying to poison memory region [%p, %p)\n",
  83            (void*)beg_addr, (void*)end_addr);
  84   }
  85   ShadowSegmentEndpoint beg(beg_addr);
  86   ShadowSegmentEndpoint end(end_addr);
  87   if (beg.chunk == end.chunk) {
  88     CHECK(beg.offset < end.offset);
  89     s8 value = beg.value;
  90     CHECK(value == end.value);
  91     // We can only poison memory if the byte in end.offset is unaddressable.
  92     // No need to re-poison memory if it is poisoned already.
  93     if (value > 0 && value <= end.offset) {
  94       if (beg.offset > 0) {
  95         *beg.chunk = Min(value, beg.offset);
  96       } else {
  97         *beg.chunk = kAsanUserPoisonedMemoryMagic;
  98       }
  99     }
 100     return;
 101   }
 102   CHECK(beg.chunk < end.chunk);
 103   if (beg.offset > 0) {
 104     // Mark bytes from beg.offset as unaddressable.
 105     if (beg.value == 0) {
 106       *beg.chunk = beg.offset;
 107     } else {
 108       *beg.chunk = Min(beg.value, beg.offset);
 109     }
 110     beg.chunk++;
 111   }
 112   REAL(memset)(beg.chunk, kAsanUserPoisonedMemoryMagic, end.chunk - beg.chunk);
 113   // Poison if byte in end.offset is unaddressable.
 114   if (end.value > 0 && end.value <= end.offset) {
 115     *end.chunk = kAsanUserPoisonedMemoryMagic;
 116   }
 117 }
 118
 119 void __asan_unpoison_memory_region(void const volatile *addr, uptr size) {
 120   if (!flags()->allow_user_poisoning || size == 0) return;
 121   uptr beg_addr = (uptr)addr;
 122   uptr end_addr = beg_addr + size;
 123   if (flags()->verbosity >= 1) {
 124     Printf("Trying to unpoison memory region [%p, %p)\n",
 125            (void*)beg_addr, (void*)end_addr);
 126   }
 127   ShadowSegmentEndpoint beg(beg_addr);
 128   ShadowSegmentEndpoint end(end_addr);
 129   if (beg.chunk == end.chunk) {
 130     CHECK(beg.offset < end.offset);
 131     s8 value = beg.value;
 132     CHECK(value == end.value);
 133     // We unpoison memory bytes up to enbytes up to end.offset if it is not
 134     // unpoisoned already.
 135     if (value != 0) {
 136       *beg.chunk = Max(value, end.offset);
 137     }
 138     return;
 139   }
 140   CHECK(beg.chunk < end.chunk);
 141   if (beg.offset > 0) {
 142     *beg.chunk = 0;
 143     beg.chunk++;
 144   }
 145   REAL(memset)(beg.chunk, 0, end.chunk - beg.chunk);
 146   if (end.offset > 0 && end.value != 0) {
 147     *end.chunk = Max(end.value, end.offset);
 148   }
 149 }
 150
 151 bool __asan_address_is_poisoned(void const volatile *addr) {
 152   return __asan::AddressIsPoisoned((uptr)addr);
 153 }
 154
 155 uptr __asan_region_is_poisoned(uptr beg, uptr size) {
 156   if (!size) return 0;
 157   uptr end = beg + size;
 158   if (!AddrIsInMem(beg)) return beg;
 159   if (!AddrIsInMem(end)) return end;
 160   uptr aligned_b = RoundUpTo(beg, SHADOW_GRANULARITY);
 161   uptr aligned_e = RoundDownTo(end, SHADOW_GRANULARITY);
 162   uptr shadow_beg = MemToShadow(aligned_b);
 163   uptr shadow_end = MemToShadow(aligned_e);
 164   // First check the first and the last application bytes,
 165   // then check the SHADOW_GRANULARITY-aligned region by calling
 166   // mem_is_zero on the corresponding shadow.
 167   if (!__asan::AddressIsPoisoned(beg) &&
 168       !__asan::AddressIsPoisoned(end - 1) &&
 169       (shadow_end <= shadow_beg ||
 170        __sanitizer::mem_is_zero((const char *)shadow_beg,
 171                                 shadow_end - shadow_beg)))
 172     return 0;
 173   // The fast check failed, so we have a poisoned byte somewhere.
 174   // Find it slowly.
 175   for (; beg < end; beg++)
 176     if (__asan::AddressIsPoisoned(beg))
 177       return beg;
 178   UNREACHABLE("mem_is_zero returned false, but poisoned byte was not found");
 179   return 0;
 180 }
 181
 182 // This is a simplified version of __asan_(un)poison_memory_region, which
 183 // assumes that left border of region to be poisoned is properly aligned.
 184 static void PoisonAlignedStackMemory(uptr addr, uptr size, bool do_poison) {
 185   if (size == 0) return;
 186   uptr aligned_size = size & ~(SHADOW_GRANULARITY - 1);
 187   PoisonShadow(addr, aligned_size,
 188                do_poison ? kAsanStackUseAfterScopeMagic : 0);
 189   if (size == aligned_size)
 190     return;
 191   s8 end_offset = (s8)(size - aligned_size);
 192   s8* shadow_end = (s8*)MemToShadow(addr + aligned_size);
 193   s8 end_value = *shadow_end;
 194   if (do_poison) {
 195     // If possible, mark all the bytes mapping to last shadow byte as
 196     // unaddressable.
 197     if (end_value > 0 && end_value <= end_offset)
 198       *shadow_end = (s8)kAsanStackUseAfterScopeMagic;
 199   } else {
 200     // If necessary, mark few first bytes mapping to last shadow byte
 201     // as addressable
 202     if (end_value != 0)
 203       *shadow_end = Max(end_value, end_offset);
 204   }
 205 }
 206
 207 void __asan_poison_stack_memory(uptr addr, uptr size) {
 208   if (flags()->verbosity > 0)
 209     Report("poisoning: %p %zx\n", (void*)addr, size);
 210   PoisonAlignedStackMemory(addr, size, true);
 211 }
 212
 213 void __asan_unpoison_stack_memory(uptr addr, uptr size) {
 214   if (flags()->verbosity > 0)
 215     Report("unpoisoning: %p %zx\n", (void*)addr, size);
 216   PoisonAlignedStackMemory(addr, size, false);
 217 }