linux-kernel - RE: [RFC PATCH v2 09/10] x86/cpu: Call ENCLS[EUPDATESVN] procedure in microcode update

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Date:   Tue, 22 Mar 2022 01:35:58 +0000
From:   "Zhang, Cathy" <cathy.zhang@...el.com>
To:     Jethro Beekman <jethro@...tanix.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Raj, Ashok" <ashok.raj@...el.com>
Subject: RE: [RFC PATCH v2 09/10] x86/cpu: Call ENCLS[EUPDATESVN] procedure in
 microcode update

Hi Jethro,

Thanks for helping review!

> -----Original Message-----
> From: Jethro Beekman <jethro@...tanix.com>
> Sent: Friday, March 18, 2022 5:06 PM
> To: Hansen, Dave <dave.hansen@...el.com>; Zhang, Cathy
> <cathy.zhang@...el.com>; linux-sgx@...r.kernel.org; linux-Hi
> kernel@...r.kernel.org
> Cc: Raj, Ashok <ashok.raj@...el.com>
> Subject: Re: [RFC PATCH v2 09/10] x86/cpu: Call ENCLS[EUPDATESVN]
> procedure in microcode update
> 
> On 2022-03-16 16:47, Dave Hansen wrote:
> > On 3/16/22 03:24, Jethro Beekman wrote:
> >>> Doing this automatically and unconditionally during a microcode
> >>> update seems undesirable. This requires the userland tooling that
> >>> is coordinating the microcode update to be aware of any SGX
> >>> enclaves that are running and possibly coordinate sequencing with
> >>> the processes containing those enclaves. This coupling does not
> >>> exist today.
> >> Also, a microcode update may not affect SGX security at all and doing
> >> the EUPDATESVN procedure may not be required for this particular
> >> update. This case is called out specifically in the EUPDATESVN
> >> documentation.
> >
> > I don't think Intel provides the metadata for the kernel to tell if an
> > update requires an EUPDATESVN procedure or not.  If this is inconvenient
> > for you, I'd suggest reporting this to the folks at Intel who can fix
> > it.  It doesn't seem like something which they are motivated to fix.
> 
> Whether or not metadata is currently made available is orthogonal to
> creating a mechanism by which userspace can indidate that a particular
> microcode update shouldn't trigger the EUPDATESVN procedure.

I'm not sure if you have noticed the discussions in v1:
https://lore.kernel.org/all/1742be9e-c18e-28c9-75c8-144bf1f6a311@intel.com/T/#m18e6fecd8c9c517c68cb4d62e53f24909abd50a7

We remove the sysfs which allows userspace to decide if and when to
trigger the EUPDATESVN procedure. Please comment if you have other
suggestion.

> 
> --
> Jethro Beekman | Fortanix