Re: How should we handle illegal task FPU state?

[Borislav Petkov]

On Thu, Oct 01, 2020 at 03:04:48PM -0700, Andy Lutomirski wrote:
> On Thu, Oct 1, 2020 at 2:50 PM Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> > I'm not sure we should ever keep running userspace after an XRSTOR*
> > failure.  For MPX, this might have provided a nice, additional vector
> > for an attacker to turn off MPX.  Same for pkeys if we didn't correctly
> > differentiate between the hardware init state versus the "software init"
> > state that we keep in init_task.
> >
> > What's the advantage of letting userspace keep running after we init its
> > state?  That it _might_ be able to recover?
> 
> I suppose we can kill userspace and change that behavior only if
> someone complains.  I still think it would be polite to try to dump
> core, but that could be tricky with the current code structure.  I'll
> try to whip up a patch.  Maybe I'll add a debugfs file to trash MXCSR
> for testing.

Just for the record, I like this: safe and simple. We can always do
smarter shenanigans later, if at all needed, that is.

-- 
Regards/Gruss,
    Boris.

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