Re: [PATCH v17 18/23] platform/x86: Intel SGX driver

[Andy Lutomirski]

On Mon, Dec 17, 2018 at 11:17 AM Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>
> On 12/17/18 11:12 AM, Andy Lutomirski wrote:
> > So I'm not saying that you shouldn't do it the way you are now, but I
> > do think that the changelog or at least some emails should explain
> > *why* the enclave needs to keep a pointer to the creating process's
> > mm.  And, if you do keep the current model, it would be nice to
> > understand what happens if you do something awful like mremap()ing an
> > enclave, or calling madvise on it, or otherwise abusing the vma.  Or
> > doing fork(), for that matter.
>
> Yeah, the code is built to have one VMA and only one VMA per enclave.
> You need to go over the origin of this restriction and what enforces this.

There is a sad historical reason that you may regret keeping this
restriction.  There are plenty of pieces of code out there that think
it's reasonable to spawn a subprocess by calling fork() and then
execve().  (This is *not* a sensible thing to do.  One should use
posix_spawn() or some CLONE_VM variant.  But even fairly recent
posix_spawn() implementations will fork().  So the driver has to do
*something* sensible on fork() or a bunch of things that use SGX
unsuspectingly via, for example, PKCS #11, are going to be very sad.
I suppose you could make enclaves just not show up in the fork()ed
children, but then you have a different problem: creating an enclave
and then doing daemon() won't work.

Yes, POSIX traditions are rather silly.