Re: [PATCH v14 09/19] x86/mm: x86/sgx: Signal SEGV_SGXERR for #PFs w/ PF_SGX

[Jarkko Sakkinen]

On Thu, 1 Nov 2018, Jarkko Sakkinen wrote:

> On Wed, 31 Oct 2018, Sean Christopherson wrote:
> > On Mon, Oct 01, 2018 at 03:03:30PM -0700, Dave Hansen wrote:
> > > On 10/01/2018 02:42 PM, Jethro Beekman wrote:
> > > > 1) Even though the vDSO function exists, userspace may still call
> > > > `ENCLU[EENTER]` manually, so the fault handling as described in the
> > > > current patch should also be maintained.
> > >
> > > Why?
> >
> > Circling back to this question, what if we take the easy way out and
> > simply signal SIGSEGV without an SGX-specific code?  I.e. treat #PF
> > with X86_PF_SGX as an access error, no more no less.  That should be
> > sufficient for userspace to function, albeit with a little more effort,
> > but presumably no more than would be needed to run on SGX1 hardware.
> >
> > AFAIK there isn't a way to prevent userspace from manually invoking
> > EENTER, short of doing some really nasty text poking or PTE swizzling.
> > We could declare using EENTER as unsupported, but that seems like
> > cutting off the nose to spite the face.  Supporting userspace EENTER
> > in a limited capacity would allow people to do whatever crazy tricks
> > they're wont to do without having to deal with absurd requests for
> > the vDSO interface.
> >
> > If we go this route we could also add the vDSO stuff after basic SGX
> > support is in mainline, obviously with approval from the powers that
> > be.
>
> Yeah, this would give stable behavior when vDSO functions are not
> available.
>
> Here's a question: if we implement this behavior, could be upstream
> series without vDSO's first and after those changes have been landed
> we would continue with the vDSO's?

Right, it was in your last paragraph, sorry. Yeah, I fully support this 
idea. It will be easier also to work on the vDSO's once we have something
landed (instead of working on a moving platform).

/Jarkko