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

[Huang, Kai]

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@xxxxxxxxxx>
> Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
> 

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