Re: [RFC PATCH v2 09/10] x86/cpu: Call ENCLS[EUPDATESVN] procedure in microcode update

From: Jethro Beekman <jethro@fortanix.com>
To: Dave Hansen <dave.hansen@intel.com>,
	Cathy Zhang <cathy.zhang@intel.com>,
	linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: ashok.raj@intel.com
Subject: Re: [RFC PATCH v2 09/10] x86/cpu: Call ENCLS[EUPDATESVN] procedure in microcode update
Date: Fri, 18 Mar 2022 10:04:37 +0100	[thread overview]
Message-ID: <abe544be-46e9-15f6-98ca-808f3d22cca7@fortanix.com> (raw)
In-Reply-To: <947c4872-df94-0091-ebbf-b733db4bd9d6@intel.com>

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On 2022-03-16 16:42, Dave Hansen wrote:
> On 3/16/22 02:46, Jethro Beekman wrote:
>>> +void update_cpusvn_intel(void) +{ +	sgx_lock_epc(); +	if
>>> (sgx_zap_pages())
>> 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.
> 
> "Today" in what?

In distros.

> If a microcode update changes SGX behavior and bumps CPUSVN, it's
> fundamentally incompatible with letting enclaves continue to run.  They
> might as well be killed.

It's not "fundamentally incompatible". It works fine today and will continue to work fine in CPUs that have EUPDATESVN support. Yes your enclaves are probably vulnerable to some attacks, but people run vulnerable software intentionally all the time.

> But, seriously, if you can't handle enclaves being killed every few
> months, don't use SGX.  The architecture doesn't allow data to be

I don't think anyone is making a claim that there are enclaves that wouldn't be able handle this? Being able to deal with something is not the same as wanting to deal with something. My laptop can handle running out of battery in the middle of writing some new code. That doesn't mean I want my laptop to arbitrarily turn off at uncontrollable times?

> persistent like normal x86.  It's fundamental to the architecture.  You
> can also think of this as a shiny new SGX *testing* feature: one that
> keeps enclave owners from becoming complacent and forgetting about what
> the SGX architecture provides.

Great idea, why not expand on this and just randomly call EREMOVE at timed intervals?

--
Jethro Beekman | Fortanix

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