Re: [PATCH 0/4 POC] Allow executing code and syscalls in another address space

[Andy Lutomirski]

On 4/13/21 10:52 PM, Andrei Vagin wrote:

> process_vm_exec has two modes:
> 
> * Execute code in an address space of a target process and stop on any
>   signal or system call.

We already have a perfectly good context switch mechanism: context
switches.  If you execute code, you are basically guaranteed to be
subject to being hijacked, which means you pretty much can't allow
syscalls.  But there's a lot of non-syscall state, and I think context
switching needs to be done with extreme care.

(Just as example, suppose you switch mms, then set %gs to point to the
LDT, then switch back.  Now you're in a weird state.  With %ss the plot
is a bit thicker.  And there are emulated vsyscalls and such.)

If you, PeterZ, and the UMCG could all find an acceptable, efficient way
to wake-and-wait so you can switch into an injected task in the target
process and switch back quickly, then I think a much nicer solution will
become available.

> 
> * Execute a system call in an address space of a target process.

I could get behind this, but there are plenty of cans of worms to watch
out for.  Serious auditing would be needed.