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systrap: Deliver SIGILL at reverted patch sites that were overwritten - #15457
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After `UnpatchSyscalls` disables syscall patching, `HandleFault` restarts any `SIGILL` raised at offset 0 or 5 of a former patch site, because it only checks that the address is in s.patches, which is never cleared. If the app has since placed code there that raises SIGILL, the restart faults again and `Switch` keeps restarting it instead of delivering the signal. At offset 5, each restart also moves RIP back 5 bytes, into whatever code now precedes the fault. s.patches is still needed to restart threads that fault while a patch is being applied or reverted, so keep it, but only restart a thread if the original "mov sysno, %eax; syscall" is still at the patch site. PiperOrigin-RevId: 994734611
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October 7, 2026 18:20
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systrap: Deliver SIGILL at reverted patch sites that were overwritten
After
UnpatchSyscallsdisables syscall patching,HandleFaultrestarts anySIGILLraised at offset 0 or 5 of a former patch site, because it only checksthat the address is in s.patches, which is never cleared. If the app
has since placed code there that raises SIGILL, the restart faults again and
Switchkeeps restarting it instead of delivering the signal. At offset 5,each restart also moves RIP back 5 bytes, into whatever code now precedes the
fault.
s.patches is still needed to restart threads that fault while a patch is being
applied or reverted, so keep it, but only restart a thread if the original
"mov sysno, %eax; syscall" is still at the patch site.