These are all frontend constructs with mostly deprecated constraints.
WaitingToStart isn't used anymore, Running is effectively always true
(and behaviour has changed that if a thread is alive, it's running).
The only one that remains is `ThreadSleeping` which is only handled in
the frontend, and there was some conflation between ThreadSleeping and
Running which was hard to gauge. So delete `Running` and
`WaitingToStart`, but move `ThreadSleeping` to the frontend.
We were using this variable for two things, letting the frontend signal
to the backend that it wants to start executing once the thread is
created, and also for handling thread pausing. These two features are
conflated with one another and actually makes things more confusing.
- Move StartRunning/StartPaused to the frontend, because its a construct
that only needs to exist in the frontend
- Adds a FEX::HLE::ThreadStateObject CV for handling pausing, which only
needs to exist for gdbserver
This is a Linux construct, move it to the frontend.
This is going to need some changes in the future since exit_group and
exit syscalls are supposed to behave differently than how FEX implements
it. For now just move it to the frontend.
We were creating a copy of the FEXCore::Core::CPUState object when we
didn't need to. We can pass the host thread's CPUState frame through to
the creation handlers since it's read-only (so modify it to be const).
We then just move the RAX and RSP setting to /after/ the CreateThread
handling instead of before.
This reduces stack usage from ~1392 bytes to ~80 bytes.
Seccomp is a relatively complex feature that was added to Linux back in
2005, and was further extended in 2013 to support BPF based protections.
Once seccomp is enabled, you can no longer disable seccomp but
additional protections can be placed on top of existing seccomp filters.
Additionally seccomp filters are inherited in child processes, which
ensures the process tree can't escape from the secure computing
environment through child processes.
The basis of this feature is a shim that lives between userspace and the
kernel at the syscall entrypoint.
In "strict" mode, seccomp only allows read, write, exit, exit_group, and {rt_,}sigreturn to function.
When in "filter" mode, a BPF filter is run on syscall entrypoint and
returns state about if the syscall should be allowed or not. Multiple
filters can be installed in this mode, all of which get executed. The
result that is the most restricted is the action that occurs at the end.
There are some significant limitations in filter mode that must be
adhered to which makes executing this code inside of kernel space a
non-issue and effectively limits how much cpu time is spent in the filters.
Although these filters are free to do basically anything with the
provided data, just can't do any loops.
FEX needs to implement seccomp because there are multiple applications
using the feature, the primary one being Chromium which some games embed
without disabling the sandbox. WINE also uses seccomp for capturing
games that do raw Windows system calls. Apparently Red Dead Redemption
is one of the games that requires this.
While FEX implements seccomp, it is not yet all encompassing, which is
one of the reasons why it isn't enabled by default and requires a config
option.
**seccomp_unotify is not implemented**
This is a relatively new feature for seccomp which lets the seccomp
filter signal an FD for multiple things. Luckily Chromium and WINE don't
use this. This will be tricky to implement under FEX since it
requires ioctl trapping and some other behaviour
**ptrace isn't supported**
One feature of seccomp is that it can raise ptrace events. Since FEX
doesn't support ptrace at all, this isn't handled. Again Chromium and
WINE don't use this.
**kill-thread not quite correct**
This isn't directly related to seccomp but more about how we do thread
shutdown in FEX. This will require some more changes around thread state
tracking before fully supporting this. Chromium and WINE don't use this.
kill-process also falls under this
Features that are supported:
- Strict mode and seccomp-bpf mode supported
- All BFP instructions that seccomp-bpf understands
- Inheriting seccomp through execve
- This means we serialize and deserialize the calling thread's
seccomp filters
- An execve that escapes FEX will also escape seccomp. Not much we
can do about it
- TSync - Allowing post-mortem seccomp insertion which allows threads to
synchronize seccomp filters after the fact
Features that are not supported:
- Different arch qualifiers depending on syscall entrypoint
- Just like our syscall handler, we are hardcoded to the arch that the
application starts with
- user_notif
- ptrace
- Runtime code cache invalidation when seccomp is installed
- Currently we must ensure all syscalls go through the frontend
syscall handler
- Runtime invalidation of code cache with inline syscalls will get
fixed in the future.
This currently isn't enabled by default because of the minor feature
problems that haven't been resolved. Currently the Linux Kernel's test
application works for the features that FEX supports, and WINE's usage
can be handled by FEX. Chromium's sandbox doesn't yet work with this PR,
but it only fails due to features unrelated to seccomp.
Having this open for merging now so we can work to resolve the remaining
issues without this bitrotting.
Two primary things here:
- Remove the static `GlobalDelegator`
- Move the thread_local SignalDelegator::ThreadState information
directly in to ThreadStateObject
Having the ThreadStateObject and the SignalDelegator information
disjoint was confusing but was required when we didn't have any object
in the frontend that could have its own independent data. Since we fixed
this with the `ThreadStateObject` type we can now move this over.
The `GlobalDelegator` object is now instead stored in
`ThreadStateObject` instead.
Instead of using a thread_local variable, we now just consume 8-bytes of
the signal alt-stack since the kernel gives us that information about
where it lives. This then converts all the thread_local usage to use
either the passed in CPU state if it exists, or fetching it from the
alt-stack offset.
Very minor changes in behaviour here, will help when trying to improve
FEX's behaviour around signals.
This has been leaked state to FEXCore for quite a while. FEXCore never
actually needed this information, moves the bits to the frontend that
are necessary.
Minor behaviour change that `RunUntilExit` now just assumes the primary
thread is using it. This behaviour is on the chopping block to get
removed next anyway.
Pulled from the seccomp WIP PR where it pulls this object more frequently.
Since it is an opaque frontend pointer it needs to be cast and we
already have a few locations that use it.
No functional change.
A bit of refactoring necessary before we can move the remaining Linux
specific code to the frontend.
Most of this taken from #3535 but attempting to be NFC as much as
possible.
Ryan Houdek