RE: [PATCH v2 2/2] x86/sgx: Implement EUPDATESVN and opportunistically call it during first EPC page alloc

[Reshetova, Elena]

> 
> On Tue, Apr 08, 2025 at 06:54:14AM +0000, Reshetova, Elena wrote:
> > >
> > > On Tue, Apr 08, 2025 at 09:40:14AM +0300, Jarkko Sakkinen wrote:
> > > > On Tue, Apr 08, 2025 at 12:06:32AM +0000, Huang, Kai wrote:
> > > > > On Mon, 2025-04-07 at 08:23 +0000, Reshetova, Elena wrote:
> > > > > > > On Fri, Apr 04, 2025 at 06:53:17AM +0000, Reshetova, Elena wrote:
> > > > > > > > > On Wed, Apr 02, 2025 at 01:11:25PM +0000, Reshetova, Elena
> > > wrote:
> > > > > > > > > > > > current SGX kernel code does not handle such errors in
> any
> > > other
> > > > > > > way
> > > > > > > > > > > > than notifying that operation failed for other ENCLS
> leaves. So,
> > > I don't
> > > > > > > > > > > > see why ENCLS[EUPDATESVN] should be different from
> > > existing
> > > > > > > > > behaviour?
> > > > > > > > > > >
> > > > > > > > > > > While not disagreeing fully (it depends on call site), in some
> > > > > > > > > > > situations it is more difficult to take more preventive
> actions.
> > > > > > > > > > >
> > > > > > > > > > > This is a situation where we know that there are *zero* EPC
> > > pages in
> > > > > > > > > > > traffic so it is relatively easy to stop the madness, isn't it?
> > > > > > > > > > >
> > > > > > > > > > > I guess the best action would be make sgx_alloc_epc_page()
> > > return
> > > > > > > > > > > consistently -ENOMEM, if the unexpected happens.
> > > > > > > > > >
> > > > > > > > > > But this would be very misleading imo. We do have memory,
> > > even page
> > > > > > > > > > allocation might function as normal in EPC, the only thing that
> is
> > > broken
> > > > > > > > > > can be EUPDATESVN functionality. Returning -ENOMEM in
> this
> > > case
> > > > > > > seems
> > > > > > > > > > wrong.
> > > > > > > > >
> > > > > > > > > This makes it not misleading at all:
> > > > > > > > >
> > > > > > > > > 	pr_err("EUPDATESVN: unknown error %d\n", ret);
> > > > > > > > >
> > > > > > > > > Since hardware should never return this, it indicates a kernel
> bug.
> > > > > > > >
> > > > > > > > OK, so you propose in this case to print the above message,
> > > sgx_updatesvn
> > > > > > > > returning an error, and then NULL from
> > > __sgx_alloc_epc_page_from_node
> > > > > > > and
> > > > > > > > the __sgx_alloc_epc_page returning -ENOMEM after an iteration
> > > over
> > > > > > > > a whole set of numa nodes given that we will keep getting the
> > > unknown
> > > > > > > error
> > > > > > > > on each node upon trying to do an allocation from each one?
> > > > > > >
> > > > > > > I'd disable ioctl's in this case and return -ENOMEM. It's a cheap
> sanity
> > > > > > > check. Should not ever happen, but if e.g., a new kernel patch
> breaks
> > > > > > > anything, it could help catching issues.
> > > > > > >
> > > > > > > We are talking here about situation that is never expected to
> happen
> > > so I
> > > > > > > don't think it is too heavy hammer here. Here it makes sense
> because
> > > not
> > > > > > > much effort is required to implement the counter-measures.
> > > > > >
> > > > > > OK, but does it really make sense to explicitly disable ioctls?
> > > > > > Note that everything *in practice* will be disabled simply because
> not a
> > > single page
> > > > > > anymore can be allocated from EPC since we are getting -ENOMEM
> on
> > > EPC
> > > > > > page allocation. Also, note that any approach we chose should be
> > > symmetrical
> > > > > > to SGX virtualization side also, which doesn´t use ioctls at all. Simply
> > > returning
> > > > > > -ENOMEM for page allocation in EPC seems like a correct
> symmetrical
> > > solution
> > > > > > that would work for both nativel enclaves and EPC pages allocated
> for
> > > VMs.
> > > > > > And nothing would  be able to proceed creating/managing enclaves
> at
> > > this point.
> > > > > >
> > > > >
> > > > > Right, failing ioctls() doesn't cover SGX virtualization.  If we ever want
> to
> > > > > fail, we should fail the EPC allocation.
> > > >
> > > > "I guess the best action would be make sgx_alloc_epc_page() return
> > > >  consistently -ENOMEM, if the unexpected happens." -me
> > > >
> > > > >
> > > > > Btw, for the unknown error, and any other errors which should not
> > > happen,
> > > > > couldn't we use the ENCLS_WARN()?  AFAICT there are already cases
> that
> > > we are
> > > > > using ENCLS_WARN() for those "impossible-to-happen-errors".
> >
> > Ok, so to summarise the approach I will be sending in the next version:
> >
> > In case unknown error returns, issue ENCLS_WARN (uses WARN_ON
> underneath)
> > and return -ENOMEM from EPC page allocation. No other explicit ioctl
> disabling needed
> > since nothing can proceed anyhow if we cannot allocate a page from EPC.
> >
> > Does this sound right?
> 
> I think it should be sufficient (not a review tho).

Sounds good, thank you! I will respin a new version soon. 

Best Regards,
Elena.