linux-kernel - RE: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <DM8PR11MB575000A8A359BA62379AD610E723A@DM8PR11MB5750.namprd11.prod.outlook.com>
Date: Mon, 4 Aug 2025 07:39:40 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: "Hansen, Dave" <dave.hansen@...el.com>
CC: "jarkko@...nel.org" <jarkko@...nel.org>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>, "mingo@...nel.org"
	<mingo@...nel.org>, "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, "Mallick, Asit K"
	<asit.k.mallick@...el.com>, "Scarlata, Vincent R"
	<vincent.r.scarlata@...el.com>, "Cai, Chong" <chongc@...gle.com>, "Aktas,
 Erdem" <erdemaktas@...gle.com>, "Annapurve, Vishal" <vannapurve@...gle.com>,
	"Bondarevska, Nataliia" <bondarn@...gle.com>, "Raynor, Scott"
	<scott.raynor@...el.com>
Subject: RE: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]



> -----Original Message-----
> From: Hansen, Dave <dave.hansen@...el.com>
> Sent: Friday, August 1, 2025 8:13 PM
> To: Reshetova, Elena <elena.reshetova@...el.com>
> Cc: jarkko@...nel.org; seanjc@...gle.com; Huang, Kai
> <kai.huang@...el.com>; mingo@...nel.org; linux-sgx@...r.kernel.org; linux-
> kernel@...r.kernel.org; x86@...nel.org; Mallick, Asit K
> <asit.k.mallick@...el.com>; Scarlata, Vincent R <vincent.r.scarlata@...el.com>;
> Cai, Chong <chongc@...gle.com>; Aktas, Erdem <erdemaktas@...gle.com>;
> Annapurve, Vishal <vannapurve@...gle.com>; Bondarevska, Nataliia
> <bondarn@...gle.com>; Raynor, Scott <scott.raynor@...el.com>
> Subject: Re: [PATCH v10 5/6] x86/sgx: Implement ENCLS[EUPDATESVN]
> 
> The changelog is missing a tidbit about the fact that this is still dead
> code until sgx_inc_usage_count() gets a real implementation.

Will add. 

> 
> On 8/1/25 04:25, Elena Reshetova wrote:
> ...
> > +/**
> > + * sgx_update_svn() - Attempt to call ENCLS[EUPDATESVN].
> > + * This instruction attempts to update CPUSVN to the
> > + * currently loaded microcode update SVN and generate new
> > + * cryptographic assets. Must be called when EPC is empty.
> 
> As a general rule, I'd much rather have the "Must be $FOO" rules written
> in code than in a comment, or along with a comment:
> 
> 	/* EPC is guaranteed to be empty when there are no users: */
> 	WARN(count, "Elevated usage count...");

I will change to do it this way. 

> 
> > + * Most of the time, there will be no update and that's OK.
> 
> This should go with the check for SGX_NO_UPDATE, not here.

Ok, will fix. 

> 
> > + * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
> > + * operation can be safely retried. In other failure cases,
> > + * the retry should not be attempted.
> 
> Ditto. This is rewriting the code in comments.

Ok, will drop. 

> 
> > + * Return:
> > + * 0: Success or not supported
> > + * -EAGAIN: Can be safely retried, failure is due to lack of
> > + *  entropy in RNG.
> > + * -EIO: Unexpected error, retries are not advisable.
> > + */
> > +static int __maybe_unused sgx_update_svn(void)
> > +{
> > +	int ret;
> > +
> > +	/*
> > +	 * If EUPDATESVN is not available, it is ok to
> > +	 * silently skip it to comply with legacy behavior.
> > +	 */
> > +	if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
> > +		return 0;
> > +
> > +	for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
> > +		ret = __eupdatesvn();
> > +
> > +		/* Stop on success or unexpected errors: */
> > +		if (ret != SGX_INSUFFICIENT_ENTROPY)
> > +			break;
> > +	}
> > +
> > +	/*
> > +	 * SVN successfully updated.
> > +	 * Let users know when the update was successful.
> > +	 */
> > +	if (!ret)
> > +		pr_info("SVN updated successfully\n");
> > +
> > +	if (!ret || ret == SGX_NO_UPDATE)
> > +		return 0;
> > +
> > +	/*
> > +	 * SVN update failed due to lack of entropy in DRNG.
> > +	 * Indicate to userspace that it should retry.
> > +	 */
> > +	if (ret == SGX_INSUFFICIENT_ENTROPY)
> > +		return -EAGAIN;
> 
> There are four cases to handle. Doesn't it make sense to just write it
> as four literal "case"s?
> 
> 	switch (ret) {
> 	case 0:
> 		pr_info("...");
> 		return 0;
> 	case SGX_NO_UPDATE:
> 		return 0;
> 	case SGX_INSUFFICIENT_ENTROPY:
> 		return -EAGAIN;
> 	default:
> 		break;
> 	}
> 
> 

Will re-write accordingly. 

Thank you very much  for your prompt review Dave!

Best Regards,
Elena.