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

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Date:   Thu, 07 May 2020 17:35:31 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Nathaniel McCallum" <npmccallum@...hat.com>,
        "Sean Christopherson" <sean.j.christopherson@...el.com>
Cc:     "Jarkko Sakkinen" <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, "Neil Horman" <nhorman@...hat.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        "Svahn, Kai" <kai.svahn@...el.com>, bp@...en8.de,
        "Josh Triplett" <josh@...htriplett.org>, luto@...nel.org,
        kai.huang@...el.com, "David Rientjes" <rientjes@...gle.com>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        "Patrick Uiterwijk" <puiterwijk@...hat.com>
Subject: Re: [PATCH v29 00/20] Intel SGX foundations

On Thu, 07 May 2020 14:34:59 -0500, Sean Christopherson  
<sean.j.christopherson@...el.com> 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@...ux.intel.com> wrote:
>> >
>> > On Wed, 06 May 2020 17:14:22 -0500, Sean Christopherson
>> > <sean.j.christopherson@...el.com> 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@...hat.com>
>> > >>
>> > >> 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);