Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention

[Ricardo Neri]

On Wed, 2017-03-08 at 17:08 +0300, Stas Sergeev wrote:
> 08.03.2017 03:32, Ricardo Neri ÐÐÑÐÑ:
> > These are the instructions covered by UMIP:
> > * SGDT - Store Global Descriptor Table
> > * SIDT - Store Interrupt Descriptor Table
> > * SLDT - Store Local Descriptor Table
> > * SMSW - Store Machine Status Word
> > * STR - Store Task Register
> >
> > This patchset initially treated tasks running in virtual-8086 mode as a
> > special case. However, I received clarification that DOSEMU[8] does not
> > support applications that use these instructions.
> Yes, this is the case.
> But at least in the past there was an attempt to
> support SLDT as it is used by an ancient pharlap
> DOS extender (currently unsupported by dosemu1/2).
> So how difficult would it be to add an optional
> possibility of delivering such SIGSEGV to userspace
> so that the kernel's dummy emulation can be overridden?

I suppose a umip=noemulation kernel parameter could be added in this
case.

> It doesn't need to be a matter of this particular
> patch set, i.e. this proposal should not trigger a
> v7 resend of all 21 patches. :) But it would be useful
> for the future development of dosemu2.

Would dosemu2 use 32-bit processes in order to keep segmentation? If it
could use 64-bit processes, emulation is not used in this case and the
SIGSEGV is delivered to user space.

Thanks and BR,
Ricardo