Miscellaneous syscalls to support running Tor#1075
Merged
robgjansen merged 10 commits intoshadow:devfrom Feb 9, 2021
robgjansen:syscall-misc2
Merged
Miscellaneous syscalls to support running Tor#1075robgjansen merged 10 commits intoshadow:devfrom robgjansen:syscall-misc2
robgjansen merged 10 commits intoshadow:devfrom
robgjansen:syscall-misc2
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Codecov Report
@@ Coverage Diff @@
## dev #1075 +/- ##
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- Coverage 55.04% 54.98% -0.06%
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Files 130 133 +3
Lines 19586 19772 +186
Branches 4676 4711 +35
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+ Hits 10781 10872 +91
- Misses 6045 6111 +66
- Partials 2760 2789 +29
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Oh I see I should enable the |
stevenengler
approved these changes
Jan 30, 2021
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Looks good!
During a meeting we discussed a few limitations of the signal support. The plan is just to document these for now.
- There's a minor issue of causality when using the native Linux signal functionality rather than implementing signals as events/tasks, but this shouldn't be important since only one process/thread per host can be running at once.
- If the plugin uses the
SIGSTOPorSIGCONTsignals, it could cause issues for ptrace mode. - In preload mode, this could cause issues for plugins that have syscall handlers. If process A sends a signal to process B, process B which is not currently running (and is waiting on a syscall) will receive the signal and start running the signal handler. The signal handler may make a syscall which gets intercepted by Shadow, and Shadow will try to make a second syscall while it's already processing the first one and will result in an error/crash.
- In preload mode, even if there is no signal handler registered, if the shim is waiting for a message from a Shadow worker (the shim is waiting on the semaphore), a signal will interrupt the wait and Shadow will continue as if the semaphore wait has finished when it hasn't.
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Another option for dealing with signals is to only allow processes to send signals to themselves, which is the approach taken in the "Reproducible Containers" paper. |
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