linux-kernel - Re: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE

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Date:   Mon, 21 Sep 2020 22:22:20 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jethro Beekman <jethro@...tanix.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Chunyang Hui <sanqian.hcy@...fin.com>,
        Jordan Hand <jorhand@...ux.microsoft.com>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        Seth Moore <sethmo@...gle.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Suresh Siddha <suresh.b.siddha@...el.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v38 14/24] x86/sgx: Add SGX_IOC_ENCLAVE_INIT

On Mon, Sep 21, 2020 at 11:10:21AM -0700, Sean Christopherson wrote:
> On Mon, Sep 21, 2020 at 07:35:14PM +0200, Borislav Petkov wrote:
> > On Tue, Sep 15, 2020 at 02:28:32PM +0300, Jarkko Sakkinen wrote:
> > > +static int sgx_einit(struct sgx_sigstruct *sigstruct, void *token,
> > > +		     struct sgx_epc_page *secs, u64 *lepubkeyhash)
> > > +{
> > > +	int ret;
> > > +
> > > +	preempt_disable();
> > > +	sgx_update_lepubkeyhash_msrs(lepubkeyhash, false);
> > 
> > So this will update the cached copies *and* the MSRs itself if what's
> > cached is stale...
> > 
> > > +	ret = __einit(sigstruct, token, sgx_get_epc_addr(secs));
> > > +	if (ret == SGX_INVALID_EINITTOKEN) {
> > 
> > ... so why would it return this error here?
> > 
> > Definition of this error says:
> > 
> >  * %SGX_INVALID_EINITTOKEN:     EINITTOKEN is invalid and enclave signer's
> >  *                              public key does not match IA32_SGXLEPUBKEYHASH.
> > 
> > when you just updated them?!
> > 
> > > +		sgx_update_lepubkeyhash_msrs(lepubkeyhash, true);
> > 
> > So why force a second time?
> 
> The LE pubkey hash MSRs are special snowflakes.  They get reset to Intel's
> default key on any loss of EPC, e.g. if the system does a suspend/resume
> cycle.  The approach we took (obviously) is to assume the kernel's cache can
> be stale at any given time.  The alternative would be to try and track loss
> of EPC conditions and emulate the reset, but that's a bit dicey on bare
> metal as any missed case would hose SGX, and in a VM it's theoretically
> impossible to handle as a particularly unhelpful VMM could emulate loss of
> EPC at will.
> 
> Yes, this need a big fat comment.

Thanks, please provide one :-)

/Jarkko