53 lines
2.9 KiB
Markdown
53 lines
2.9 KiB
Markdown
## General things
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### Thread-locals
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Right now we don't use any thread-local stuff in zig. This means that the application can freely
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decide what to do with the `fs` segment. If we need some thread-locals in the future we have to
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carefully think about how to do it.
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If `FSGSBASE` is available we can swap out the segment real fast. If not we would need to fallback
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to `arch_prctl` which is of course a lot slower. Fortunately `FSGSBASE` is available since Intel
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IvyBridge(2012) and AMD Zen 2 Family 17H(2019) and Linux 5.9(2020).
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## Major things
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- [x] `clone`: with and without stack switching
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- [x] `clone3`: with and without stack switching
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- [x] `fork`: likely there is nothing to be done here but just to be sure, check again
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- [x] `rt_sigreturn`: we can't use the normal `syscall` interception because we push something onto
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the stack, so `ucontext` isn't on top anymore.
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- [x] `/proc/self/exe`: intercept calls to `readlink`/`readlinkat` with that as argument
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- [x] `auxv`: check if that is setup correctly and completely
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- [x] JIT support: intercept `mmap`, `mprotect` and `mremap` that change pages to be executable
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- [ ] `SIGILL` patching fallback
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- [x] `vdso` handling
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- [x] check why the libc tests are flaky
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## Minor things
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- [ ] Cleanup: When a JIT engine frees code, our trampolines are "zombies", so over time we leak
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memory and also reduce the patching percentage
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- [ ] Ghost page edge case: In all patch strategies, if a range spans multiple pages and we `mmap`
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the first one but can't `mmap` the second one we just let the first one mapped. It would be better
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to unmap them
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- [ ] Right now when patching we mmap a page and may not use it, but we still leave it mapped. This
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leaks memory. If we fix this correctly the Ghost page issue is also fixed
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- [ ] Re-entrancy for `patchRegion`
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- when a signal comes, while we are in that function, and we need to patch something due to the
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signal we will deadlock
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- [ ] strict disassembly mode: currently we warn on disassembly error, provide a flag to stop instead
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- [ ] Separate stack for flicker
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- when the application is run with a small stack (`sigaltstack`, goroutines) we might overflow
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especially for the `patchRegion` call
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- either one global stack for all to use(with a mutex) or a thread-local stack (though using
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`fs` has other problems)
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- [ ] `exec`: option to persist across `exec` calls, useful for things like `make`
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- [ ] `prctl`/`arch_prctl`: check if/what we need to intercept and change
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- [ ] `seccomp`: check what we need to intercept and change
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- [ ] `modify_ldt`: check what we need to intercept and change
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- [ ] `set_tid_address`: check what we need to intercept and change
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- [ ] performance optimizations for patched code? Peephole might be possible
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- [ ] maybe add a way to run something after the client is finished
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- could be useful for statistics, cleanup(if necessary), or notifying of suppressed warnings
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