linux-kernel - Re: [PATCH v14 5/5] x86/sgx: Enable automatic SVN updates for SGX enclaves

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Message-ID: <a75801b6bf56362c0ac9fd4ac2f82f3133b55f1a.camel@intel.com>
Date: Thu, 14 Aug 2025 09:36:30 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Reshetova, Elena" <elena.reshetova@...el.com>, "Hansen, Dave"
	<dave.hansen@...el.com>
CC: "seanjc@...gle.com" <seanjc@...gle.com>, "mingo@...nel.org"
	<mingo@...nel.org>, "Scarlata, Vincent R" <vincent.r.scarlata@...el.com>,
	"x86@...nel.org" <x86@...nel.org>, "jarkko@...nel.org" <jarkko@...nel.org>,
	"Annapurve, Vishal" <vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Aktas, Erdem" <erdemaktas@...gle.com>, "Cai, Chong" <chongc@...gle.com>,
	"Bondarevska, Nataliia" <bondarn@...gle.com>, "linux-sgx@...r.kernel.org"
	<linux-sgx@...r.kernel.org>, "Raynor, Scott" <scott.raynor@...el.com>
Subject: Re: [PATCH v14 5/5] x86/sgx: Enable automatic SVN updates for SGX
 enclaves

On Thu, 2025-08-14 at 10:34 +0300, Reshetova, Elena wrote:
> == Background ==
> 
> ENCLS[EUPDATESVN] is a new SGX instruction [1] which allows enclave
> attestation to include information about updated microcode SVN without a
> reboot. Before an EUPDATESVN operation can be successful, all SGX memory
> (aka. EPC) must be marked as “unused” in the SGX hardware metadata
> (aka.EPCM). This requirement ensures that no compromised enclave can
> survive the EUPDATESVN procedure and provides an opportunity to generate
> new cryptographic assets.
> 
> == Solution ==
> 
> Attempt to execute ENCLS[EUPDATESVN] every time the first file descriptor
> is obtained via sgx_(vepc_)open(). In the most common case the microcode
> SVN is already up-to-date, and the operation succeeds without updating SVN.
> 
> Note: while in such cases the underlying crypto assets are regenerated, it
> does not affect enclaves' visible keys obtained via EGETKEY instruction.
> 
> If it fails with any other error code than SGX_INSUFFICIENT_ENTROPY, this
> is considered unexpected and the *open() returns an error. This should not
> happen in practice.
> 
> On contrary, SGX_INSUFFICIENT_ENTROPY might happen due to a pressure on the
> system's DRNG (RDSEED) and therefore the *open() can be safely retried to
> allow normal enclave operation.
> 
> [1] Runtime Microcode Updates with Intel Software Guard Extensions,
> https://cdrdv2.intel.com/v1/dl/getContent/648682
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
> Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> 

Reviewed-by: Kai Huang <kai.huang@...el.com>