Re: [PATCH v29 00/20] Intel SGX foundations

[Haitao Huang]

On Thu, 07 May 2020 14:34:59 -0500, Sean Christopherson  
<sean.j.christopherson@xxxxxxxxx> wrote:

> On Thu, May 07, 2020 at 12:49:15PM -0400, Nathaniel McCallum wrote:
> > On Thu, May 7, 2020 at 1:03 AM Haitao Huang
> > <haitao.huang@xxxxxxxxxxxxxxx> wrote:
> > >
> > > On Wed, 06 May 2020 17:14:22 -0500, Sean Christopherson
> > > <sean.j.christopherson@xxxxxxxxx> wrote:
> > >
> > > > On Wed, May 06, 2020 at 05:42:42PM -0400, Nathaniel McCallum wrote:
> > > >> Tested on Enarx. This requires a patch[0] for v29 support.
> > > >>
> > > >> Tested-by: Nathaniel McCallum <npmccallum@xxxxxxxxxx>
> > > >>
> > > >> However, we did uncover a small usability issue. See below.
> > > >>
> > > >> [0]:
> > > >>  
> > https://github.com/enarx/enarx/pull/507/commits/80da2352aba46aa7bc6b4d1fccf20fe1bda58662
> > > >
> > > > ...
> > > >
> > > >> > * Disallow mmap(PROT_NONE) from /dev/sgx. Any mapping (e.g.
> > > >> anonymous) can
> > > >> >   be used to reserve the address range. Now /dev/sgx supports  
> > only
> > > >> opaque
> > > >> >   mappings to the (initialized) enclave data.
> > > >>
> > > >> The statement "Any mapping..." isn't actually true.
>
> Yeah, this definitely misleading.  I haven't looked at our most recent  
> docs,
> but I'm going to go out on a limb and assume we haven't documented the
> preferred mechanism for carving out virtual memory for the enclave.  That
> absolutely should be done.
>
> > > >> Enarx creates a large enclave (currently 64GiB). This worked when  
> > we
> > > >> created a file-backed mapping on /dev/sgx/enclave. However,  
> > switching
> > > >> to an anonymous mapping fails with ENOMEM. We suspect this is  
> > because
> > > >> the kernel attempts to allocate all the pages and zero them but  
> > there
> > > >> is insufficient RAM available. We currently work around this by
> > > >> creating a shared mapping on /dev/zero.
> > > >
> > > > Hmm, the kernel shouldn't actually allocate physical pages unless  
> > they're
> > > > written.  I'll see if I can reproduce.
> > > >
> > >
> > > For larger size mmap, I think it requires enabling vm overcommit mode  
> > 1:
> > > echo 1 | sudo tee /proc/sys/vm/overcommit_memory
>
> It shouldn't unless the initial mmap is "broken".  Not truly broken, but
> broken in the sense that what Enarx is asking for is not actually what it
> desires.
So I tried, this passes with mode 1 but fail with ENOMEM by default:

mmap(NULL, 0x100000000000UL, PROT_NONE, MAP_SHARED| MAP_ANONYMOUS, -1, 0);