The pointer is allowed to be null or garbage if the number of nfds
passed in is zero.
Unify the x86 and x86-64 implementations to ensure consistency.
Fixes Warhammer 40k: Relics of War
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.
This must have happened during a refactor or something, but since we're
making a copy of the function pointers, it would have only gotten the
version /prior/ to loading host VDSO symbols.
Moves the VDSO thunk definition setting to the end after VDSO symbol
definitions in order to get host VDSO symbols working again.
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.
These are a Linux construct and should live here. Removes a weird
passthrough API from FEXCore and keeps it in the frontend instead.
This isn't even typically allocated in a real setup, as it's only a
fallback for if VDSO isn't loaded.
The CallbackReturn function stays in FEXCore because it would have
caused an API in the other direction instead.
For the remaining syscalls we need to introduce some new concepts around
checking if pointers and string arrays are readable and I don't want to
do that yet.
No functional change, just moving the code.
This is entirely freestanding from the rest of the signal delegator
handling and mostly gets in the way when I'm working with the rest of
the signal handling. Separate it out to improve readability.
Fairly trivial because we already supported deferring these signals. We
had just failed the final step of blocking the signal if we can't block
the signal (like with SIGSEGV, SIGBUS, etc).
Once the guest unblocks the signal mask with sigprocmask, the signal
will fire again.
Apparently older glibc relied on this behaviour for signal raising which
this fixes.
With the previous Copy{To,From}User helpers we need to actually
implement the handlers correctly. We want something that is a bit
lighter so we don't need to implement the faulting path in the syscall
handlers.
Implements a handful of helpers that just check for readable and
writable capability which can be thrown in to an assertion handler that
is zero cost in release mode.
Readable is checked by just attempting to read all bytes.
Writable is checked by attempting to read each byte and writing it back
to the same location.
Uses these helpers in x64/FD.cpp to showcase how they will be used to
detect EFAULT. Tested locally that they work correctly by writing some
small tests for the syscalls that expect EFAULT.
- We can have the SyscallFunctionDefinitions be the correct size out of
the gate. Both tables are always 512 entries in size.
- In the RegisterSyscall_{32,64} handlers, just get the reference using
operator[]. We always know we will be under the size of the array, add
a an assert to check. Removes a bit of vector range checking overhead.
- Namespace 32-bit syscalls like 64-bit syscalls and include in the
regular header like 64-bit. This was just an oversight
- Use std::fill for the syscall gap for the invalid syscall, just a
minor cleanup.
No functional change.
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.
Instead of passing the TID back to the exit handler, just pass the whole
thread object. This will allow some cleanups with the frontend thread
tracking soon
NFC
We support leaf functions now, so add the few that were calling for it.
We will be gaining support for the xsave ones relatively soon, so its
good to have them supported.
Also deletes a couple of cdt/cqm things that aren't exposed and we won't
be supporting.
Removes a global static initializer for the vector and its atexit
handler.
This handler array can be consteval similar to the x86 tables so it can
be generated entirely at compile time.
This causes a global initializer that registers an atexit handler.
Be smarter, use an std::array and pass its data around using a span
instead.
Removes the global initializer and removes the atexit installation
At the moment we always run ctest with max number of cpus. If
undefined, it will keep current behaviour, otherwise it will
honour TEST_JOB_COUNT.
Therefore to run ctest one test at a time, use
`cmake ... -DTEST_JOB_COUNT=1`
Some applications don't measure rdtsc correctly and instead use cpuinfo
to get the CPU core's base clock speed. Which for most x86 CPUs is the
base clock speed which also matches their cycle counter speed.
Did this as a quick test to see if this would help `Unbound: Worlds
Apart` stuttering while BinaryNinja was disassembling the binary.
Turns out the game doesn't use cpuinfo for its cycle counter speed
determination, but it is good to implement this regardless.
Ryan Houdek