linux-kernel - Re: [PATCH v39 05/24] x86/sgx: Add wrappers for ENCLS leaf functions

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Date:   Mon, 19 Oct 2020 10:38:41 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jethro Beekman <jethro@...tanix.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, bp@...en8.de, cedric.xing@...el.com,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, haitao.huang@...el.com, kai.huang@...el.com,
        kai.svahn@...el.com, kmoy@...gle.com, ludloff@...gle.com,
        luto@...nel.org, nhorman@...hat.com, npmccallum@...hat.com,
        puiterwijk@...hat.com, rientjes@...gle.com, tglx@...utronix.de,
        yaozhangx@...gle.com, mikko.ylinen@...el.com
Subject: Re: [PATCH v39 05/24] x86/sgx: Add wrappers for ENCLS leaf functions

On Mon, Oct 19, 2020 at 07:30:32AM -0700, Dave Hansen wrote:
> On 10/2/20 9:50 PM, Jarkko Sakkinen wrote:
> > +/**
> > + * encls_failed() - Check if an ENCLS leaf function failed
> > + * @ret:	the return value of an ENCLS leaf function call
> > + *
> > + * Check if an ENCLS leaf function failed. This happens when the leaf function
> > + * causes a fault that is not caused by an EPCM conflict or when the leaf
> > + * function returns a non-zero value.
> > + */
> > +static inline bool encls_failed(int ret)
> > +{
> > +	int epcm_trapnr;
> > +
> > +	if (boot_cpu_has(X86_FEATURE_SGX2))
> > +		epcm_trapnr = X86_TRAP_PF;
> > +	else
> > +		epcm_trapnr = X86_TRAP_GP;
> 
> So, the SDM makes it sound like the only thing that changes from
> SGX1->SGX2 is the ENCLS leafs supported.  Since the kernel doesn't use
> any SGX2 leaf functions, this would imply there is some other
> architecture change which is visible.  *But* I don't see any evidence of
> this in the SDM, at least from a quick scan.
> 
> Why is this here?

SGX1 CPUs take an erratum on the #PF behavior, e.g. "KBW90 Violation of Intel
SGX Access-Control Requirements Produce #GP Instead of #PF".

https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/xeon-e3-1200v6-spec-update.pdf

> > +	if (ret & ENCLS_FAULT_FLAG)
> > +		return ENCLS_TRAPNR(ret) != epcm_trapnr;
> > +
> > +	return !!ret;
> > +}
> 
>