x86 User-Mode Instruction Prevention and winehq

[Neri, Ricardo]

On Fri, 2016-11-18 at 10:56 -0600, Alexandre Julliard wrote:
> "Neri, Ricardo" <ricardo.neri at intel.com> writes:
> 
> > If running in protected mode, always propagate the GP fault to the user
> > space via a sigsegv. If running in vm86 mode, trap the GP fault within
> > the kernel and give the userspace fake values for the aforementioned
> > resources (most likely zeros).
> >
> > Also, UMIP will be able to be disabled via a kernel command-line
> > parameter at boot.
> >
> > I would like to inquire about the current use of these instructions and
> > whether it would be catastrophic for wine to lose access to them.
> 
> There are apps that use these instructions, so we'll need to catch and
> emulate them in the segfault handler. We have the infrastructure in
> place for that sort of thing so it shouldn't be hard. It does mean that
> these apps would get broken until users upgrade Wine though.

Thanks for the feedback. The consensus in the kernel mailing list is to
catch the gp fault within the kernel and give the userspace fake values
for the GDT, LDT, IDT and the MSW (I don't think there are vm86 apps
that use the task register, are they?). This is because the goal of the
feature is to hide these tables from the user space. Would this be a
problem?
>