Itamar f9d62fd5e5 LibDebug: Make sure to not single step the program twice ...

After hitting a breakpoint, we single step the program to execute the
instruction we breaked on and re-enable the breakpoint.
We also single step the program when the user of LibDebug returned a
DebugDecision::SingleStep.

Previously, if we hit a breakpoint and then were asked to to a
DebugDecision::SingleStep, we would single step twice.

This bug can actually crash programs, because it might cause us to
skip over a patched INT3 instruction in the second single-step.

Interestingely enough, this bug manifested as functrace crashing
certain programs: after hitting a breakpoint on a CALL instruction,
functrace single steps the program to see where the CALL jumps to
(yes, this can be optimized :D). functrace crashed when a CALL
instruction jumps to another CALL, because it inserts breakpoints on CALL
instructions, and so the INT3 in the 2nd CALL was skipped over, and we
executed garbage :).

This commit fixes this by making sure not to single-step twice.

2020-05-24 10:42:21 +02:00

7.4 KiB

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