lkml.org 
[lkml]   [2018]   [Sep]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing enclaves
Date

> -----Original Message-----
> From: platform-driver-x86-owner@vger.kernel.org [mailto:platform-driver-x86-
> owner@vger.kernel.org] On Behalf Of Sean Christopherson
> Sent: Wednesday, September 5, 2018 4:36 AM
> To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> Cc: Huang, Kai <kai.huang@intel.com>; platform-driver-x86@vger.kernel.org;
> x86@kernel.org; nhorman@redhat.com; linux-kernel@vger.kernel.org;
> tglx@linutronix.de; suresh.b.siddha@intel.com; Ayoun, Serge
> <serge.ayoun@intel.com>; hpa@zytor.com; npmccallum@redhat.com;
> mingo@redhat.com; linux-sgx@vger.kernel.org; Hansen, Dave
> <dave.hansen@intel.com>
> Subject: Re: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing enclaves
>
> On Tue, Sep 04, 2018 at 06:30:21PM +0300, Jarkko Sakkinen wrote:
> > On Tue, Sep 04, 2018 at 07:54:51AM -0700, Sean Christopherson wrote:
> > > I don't see any value in trying to rule out specific causes of
> > > INVALID_TOKEN, but we should only retry EINIT if ret==INVALID_TOKEN
> > > and RDMSR(HASH0) != sgx_lepubkeyhash[0]. Only the first MSR needs
> > > to be checked for validity as they're a package deal, i.e. they'll
> > > all be valid or all be reset. There shouldn't be a limit on retry
> > > attempts, e.g. the MSRs could theoretically be reset between WRMSR and
> EINIT.
> >
> > Why is doing rdmsrs necessary? With the INVALID_TOKEN error we know we
> > are out-of-sync i.e. have been sleeping and then one just needs to do
> > wrmsrs.
>
> As Kai mentioned, INVALID_TOKEN is returned for other reasons, e.g. a
> production enclave trying to use a debug token or reserved bits set in the token.
> And in the KVM case, the hash and token are provided by the guest, so it's
> entirely possible the enclave/token is not signed with the key specified in the
> hash. RDMSR is relatively inexpensive compared to the overall cost of EINIT.
> Though of course EINIT failure isn't exactly a fast path, so I'm ok if you want to
> opt for simplicity and retry on INVALID_TOKEN without checking the MSRs, just
> make sure to add a comment indicating we're intentionally not checking the
> MSRs.
>
> > I think one retry should be enough given that VMM traps EINIT. One
> > retry is needed to take care of the guest itself (or host if we are
> > running on bare metal) having been in a sleep state.
>
> Assuming we do RDMSR(hash0), that should be sufficient to prevent infinite retry
> and

IMHO probably we need to review this assumption w/ crypto guys, at least Intel internally.

Thanks,
-Kai

it protects against the MSRs being lost between WRMSR and EINIT during
> retry. That being said, I'm ok retrying only once, especially if you want to omit
> the RDMSR. Disabling preemption should prevent the kernel from suspending
> between WRMSR and EINIT, I'm just being paranoid.


\
 
 \ /
  Last update: 2018-09-05 00:14    [W:0.084 / U:29.912 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site