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| 1 | +//===-- dfsan.cc ----------------------------------------------------------===// |
| 2 | +// |
| 3 | +// The LLVM Compiler Infrastructure |
| 4 | +// |
| 5 | +// This file is distributed under the University of Illinois Open Source |
| 6 | +// License. See LICENSE.TXT for details. |
| 7 | +// |
| 8 | +//===----------------------------------------------------------------------===// |
| 9 | +// |
| 10 | +// This file is a part of DataFlowSanitizer. |
| 11 | +// |
| 12 | +// DataFlowSanitizer runtime. This file defines the public interface to |
| 13 | +// DataFlowSanitizer as well as the definition of certain runtime functions |
| 14 | +// called automatically by the compiler (specifically the instrumentation pass |
| 15 | +// in llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp). |
| 16 | +// |
| 17 | +// The public interface is defined in include/sanitizer/dfsan_interface.h whose |
| 18 | +// functions are prefixed dfsan_ while the compiler interface functions are |
| 19 | +// prefixed __dfsan_. |
| 20 | +//===----------------------------------------------------------------------===// |
| 21 | + |
| 22 | +#include "sanitizer/dfsan_interface.h" |
| 23 | +#include "sanitizer_common/sanitizer_atomic.h" |
| 24 | +#include "sanitizer_common/sanitizer_common.h" |
| 25 | +#include "sanitizer_common/sanitizer_libc.h" |
| 26 | + |
| 27 | +typedef atomic_uint16_t atomic_dfsan_label; |
| 28 | +static const dfsan_label kInitializingLabel = -1; |
| 29 | + |
| 30 | +static const uptr kNumLabels = 1 << (sizeof(dfsan_label) * 8); |
| 31 | + |
| 32 | +static atomic_dfsan_label __dfsan_last_label; |
| 33 | +static dfsan_label_info __dfsan_label_info[kNumLabels]; |
| 34 | + |
| 35 | +SANITIZER_INTERFACE_ATTRIBUTE THREADLOCAL dfsan_label __dfsan_retval_tls; |
| 36 | +SANITIZER_INTERFACE_ATTRIBUTE THREADLOCAL dfsan_label __dfsan_arg_tls[64]; |
| 37 | + |
| 38 | +// On Linux/x86_64, memory is laid out as follows: |
| 39 | +// |
| 40 | +// +--------------------+ 0x800000000000 (top of memory) |
| 41 | +// | application memory | |
| 42 | +// +--------------------+ 0x700000008000 (kAppAddr) |
| 43 | +// | | |
| 44 | +// | unused | |
| 45 | +// | | |
| 46 | +// +--------------------+ 0x200200000000 (kUnusedAddr) |
| 47 | +// | union table | |
| 48 | +// +--------------------+ 0x200000000000 (kUnionTableAddr) |
| 49 | +// | shadow memory | |
| 50 | +// +--------------------+ 0x000000010000 (kShadowAddr) |
| 51 | +// | reserved by kernel | |
| 52 | +// +--------------------+ 0x000000000000 |
| 53 | +// |
| 54 | +// To derive a shadow memory address from an application memory address, |
| 55 | +// bits 44-46 are cleared to bring the address into the range |
| 56 | +// [0x000000008000,0x100000000000). Then the address is shifted left by 1 to |
| 57 | +// account for the double byte representation of shadow labels and move the |
| 58 | +// address into the shadow memory range. See the function shadow_for below. |
| 59 | + |
| 60 | +typedef atomic_dfsan_label dfsan_union_table_t[kNumLabels][kNumLabels]; |
| 61 | + |
| 62 | +static const uptr kShadowAddr = 0x10000; |
| 63 | +static const uptr kUnionTableAddr = 0x200000000000; |
| 64 | +static const uptr kUnusedAddr = kUnionTableAddr + sizeof(dfsan_union_table_t); |
| 65 | +static const uptr kAppAddr = 0x700000008000; |
| 66 | + |
| 67 | +static atomic_dfsan_label *union_table(dfsan_label l1, dfsan_label l2) { |
| 68 | + return &(*(dfsan_union_table_t *) kUnionTableAddr)[l1][l2]; |
| 69 | +} |
| 70 | + |
| 71 | +static dfsan_label *shadow_for(void *ptr) { |
| 72 | + return (dfsan_label *) ((((uintptr_t) ptr) & ~0x700000000000) << 1); |
| 73 | +} |
| 74 | + |
| 75 | +// Resolves the union of two unequal labels. Nonequality is a precondition for |
| 76 | +// this function (the instrumentation pass inlines the equality test). |
| 77 | +extern "C" SANITIZER_INTERFACE_ATTRIBUTE |
| 78 | +dfsan_label __dfsan_union(dfsan_label l1, dfsan_label l2) { |
| 79 | + DCHECK_NE(l1, l2); |
| 80 | + |
| 81 | + if (l1 == 0) |
| 82 | + return l2; |
| 83 | + if (l2 == 0) |
| 84 | + return l1; |
| 85 | + |
| 86 | + if (l1 > l2) |
| 87 | + Swap(l1, l2); |
| 88 | + |
| 89 | + atomic_dfsan_label *table_ent = union_table(l1, l2); |
| 90 | + // We need to deal with the case where two threads concurrently request |
| 91 | + // a union of the same pair of labels. If the table entry is uninitialized, |
| 92 | + // (i.e. 0) use a compare-exchange to set the entry to kInitializingLabel |
| 93 | + // (i.e. -1) to mark that we are initializing it. |
| 94 | + dfsan_label label = 0; |
| 95 | + if (atomic_compare_exchange_strong(table_ent, &label, kInitializingLabel, |
| 96 | + memory_order_acquire)) { |
| 97 | + // Check whether l2 subsumes l1. We don't need to check whether l1 |
| 98 | + // subsumes l2 because we are guaranteed here that l1 < l2, and (at least |
| 99 | + // in the cases we are interested in) a label may only subsume labels |
| 100 | + // created earlier (i.e. with a lower numerical value). |
| 101 | + if (__dfsan_label_info[l2].l1 == l1 || |
| 102 | + __dfsan_label_info[l2].l2 == l1) { |
| 103 | + label = l2; |
| 104 | + } else { |
| 105 | + label = |
| 106 | + atomic_fetch_add(&__dfsan_last_label, 1, memory_order_relaxed) + 1; |
| 107 | + CHECK_NE(label, kInitializingLabel); |
| 108 | + __dfsan_label_info[label].l1 = l1; |
| 109 | + __dfsan_label_info[label].l2 = l2; |
| 110 | + } |
| 111 | + atomic_store(table_ent, label, memory_order_release); |
| 112 | + } else if (label == kInitializingLabel) { |
| 113 | + // Another thread is initializing the entry. Wait until it is finished. |
| 114 | + do { |
| 115 | + internal_sched_yield(); |
| 116 | + label = atomic_load(table_ent, memory_order_acquire); |
| 117 | + } while (label == kInitializingLabel); |
| 118 | + } |
| 119 | + return label; |
| 120 | +} |
| 121 | + |
| 122 | +extern "C" SANITIZER_INTERFACE_ATTRIBUTE |
| 123 | +dfsan_label __dfsan_union_load(dfsan_label *ls, size_t n) { |
| 124 | + dfsan_label label = ls[0]; |
| 125 | + for (size_t i = 1; i != n; ++i) { |
| 126 | + dfsan_label next_label = ls[i]; |
| 127 | + if (label != next_label) |
| 128 | + label = __dfsan_union(label, next_label); |
| 129 | + } |
| 130 | + return label; |
| 131 | +} |
| 132 | + |
| 133 | +extern "C" SANITIZER_INTERFACE_ATTRIBUTE |
| 134 | +void *__dfsan_memcpy(void *dest, const void *src, size_t n) { |
| 135 | + dfsan_label *sdest = shadow_for(dest), *ssrc = shadow_for((void *)src); |
| 136 | + internal_memcpy((void *)sdest, (void *)ssrc, n * sizeof(dfsan_label)); |
| 137 | + return internal_memcpy(dest, src, n); |
| 138 | +} |
| 139 | + |
| 140 | +SANITIZER_INTERFACE_ATTRIBUTE |
| 141 | +dfsan_label dfsan_create_label(const char *desc, void *userdata) { |
| 142 | + dfsan_label label = |
| 143 | + atomic_fetch_add(&__dfsan_last_label, 1, memory_order_relaxed) + 1; |
| 144 | + CHECK_NE(label, kInitializingLabel); |
| 145 | + __dfsan_label_info[label].l1 = __dfsan_label_info[label].l2 = 0; |
| 146 | + __dfsan_label_info[label].desc = desc; |
| 147 | + __dfsan_label_info[label].userdata = userdata; |
| 148 | + __dfsan_retval_tls = 0; // Ensures return value is unlabelled in the caller. |
| 149 | + return label; |
| 150 | +} |
| 151 | + |
| 152 | +SANITIZER_INTERFACE_ATTRIBUTE |
| 153 | +void dfsan_set_label(dfsan_label label, void *addr, size_t size) { |
| 154 | + for (dfsan_label *labelp = shadow_for(addr); size != 0; --size, ++labelp) |
| 155 | + *labelp = label; |
| 156 | +} |
| 157 | + |
| 158 | +SANITIZER_INTERFACE_ATTRIBUTE |
| 159 | +void dfsan_add_label(dfsan_label label, void *addr, size_t size) { |
| 160 | + for (dfsan_label *labelp = shadow_for(addr); size != 0; --size, ++labelp) |
| 161 | + if (*labelp != label) |
| 162 | + *labelp = __dfsan_union(*labelp, label); |
| 163 | +} |
| 164 | + |
| 165 | +SANITIZER_INTERFACE_ATTRIBUTE dfsan_label dfsan_get_label(long data) { |
| 166 | + // The label for 'data' is implicitly passed by the instrumentation pass in |
| 167 | + // the first element of __dfsan_arg_tls. So we can just return it. |
| 168 | + __dfsan_retval_tls = 0; // Ensures return value is unlabelled in the caller. |
| 169 | + return __dfsan_arg_tls[0]; |
| 170 | +} |
| 171 | + |
| 172 | +SANITIZER_INTERFACE_ATTRIBUTE |
| 173 | +const struct dfsan_label_info *dfsan_get_label_info(dfsan_label label) { |
| 174 | + __dfsan_retval_tls = 0; // Ensures return value is unlabelled in the caller. |
| 175 | + return &__dfsan_label_info[label]; |
| 176 | +} |
| 177 | + |
| 178 | +int dfsan_has_label(dfsan_label label, dfsan_label elem) { |
| 179 | + __dfsan_retval_tls = 0; // Ensures return value is unlabelled in the caller. |
| 180 | + if (label == elem) |
| 181 | + return true; |
| 182 | + const dfsan_label_info *info = dfsan_get_label_info(label); |
| 183 | + if (info->l1 != 0) { |
| 184 | + return dfsan_has_label(info->l1, elem) || dfsan_has_label(info->l2, elem); |
| 185 | + } else { |
| 186 | + return false; |
| 187 | + } |
| 188 | +} |
| 189 | + |
| 190 | +dfsan_label dfsan_has_label_with_desc(dfsan_label label, const char *desc) { |
| 191 | + __dfsan_retval_tls = 0; // Ensures return value is unlabelled in the caller. |
| 192 | + const dfsan_label_info *info = dfsan_get_label_info(label); |
| 193 | + if (info->l1 != 0) { |
| 194 | + return dfsan_has_label_with_desc(info->l1, desc) || |
| 195 | + dfsan_has_label_with_desc(info->l2, desc); |
| 196 | + } else { |
| 197 | + return internal_strcmp(desc, info->desc) == 0; |
| 198 | + } |
| 199 | +} |
| 200 | + |
| 201 | +#ifdef DFSAN_NOLIBC |
| 202 | +extern "C" void dfsan_init() { |
| 203 | +#else |
| 204 | +static void dfsan_init(int argc, char **argv, char **envp) { |
| 205 | +#endif |
| 206 | + MmapFixedNoReserve(kShadowAddr, kUnusedAddr - kShadowAddr); |
| 207 | + |
| 208 | + // Protect the region of memory we don't use, to preserve the one-to-one |
| 209 | + // mapping from application to shadow memory. But if ASLR is disabled, Linux |
| 210 | + // will load our executable in the middle of our unused region. This mostly |
| 211 | + // works so long as the program doesn't use too much memory. We support this |
| 212 | + // case by disabling memory protection when ASLR is disabled. |
| 213 | + uptr init_addr = (uptr)&dfsan_init; |
| 214 | + if (!(init_addr >= kUnusedAddr && init_addr < kAppAddr)) |
| 215 | + Mprotect(kUnusedAddr, kAppAddr - kUnusedAddr); |
| 216 | +} |
| 217 | + |
| 218 | +#ifndef DFSAN_NOLIBC |
| 219 | +__attribute__((section(".preinit_array"), used)) |
| 220 | +static void (*dfsan_init_ptr)(int, char **, char **) = dfsan_init; |
| 221 | +#endif |
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