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

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Message-ID: <20200921182753.GK5901@zn.tnic>
Date:   Mon, 21 Sep 2020 20:27:53 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Sean Christopherson <sean.j.christopherson@...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>,
        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:
> 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.

Lemme try to understand this: the system could suspend/resume right
here:

        sgx_update_lepubkeyhash_msrs(lepubkeyhash, false);

<--- suspend/resume

        ret = __einit(sigstruct, token, sgx_get_epc_addr(secs));

and thus the MSRs would have the default key so you'd need the second
__einit() call?

But what happens if the system suspends before the second __einit()
call?

Why don't you simply drop that @enforce param and let the caller handle
any retries?

Or is the scenario something different?

Or you could perhaps disable suspend/resume around it, maybe something
like lock_system_sleep() or so, from a quick grep...

> Yes, this need a big fat comment.

Oh yeah.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette