linux-kernel - Re: [PATCH v29 00/20] Intel SGX foundations

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Date:   Wed, 29 Apr 2020 08:14:59 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     "Dr. Greg" <greg@...ellic.com>, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, nhorman@...hat.com, npmccallum@...hat.com,
        haitao.huang@...el.com, andriy.shevchenko@...ux.intel.com,
        tglx@...utronix.de, kai.svahn@...el.com, bp@...en8.de,
        josh@...htriplett.org, luto@...nel.org, kai.huang@...el.com,
        rientjes@...gle.com, cedric.xing@...el.com, puiterwijk@...hat.com
Subject: Re: [PATCH v29 00/20] Intel SGX foundations

On Wed, Apr 29, 2020 at 08:23:29AM +0300, Jarkko Sakkinen wrote:
> On Sun, Apr 26, 2020 at 11:57:53AM -0500, Dr. Greg wrote:
> > On Wed, Apr 22, 2020 at 12:52:56AM +0300, Jarkko Sakkinen wrote:
> > 
> > Good day, I hope the weekend is going well for everyone.
> > 
> > > Intel(R) SGX is a set of CPU instructions that can be used by applications
> > > to set aside private regions of code and data. The code outside the enclave
> > > is disallowed to access the memory inside the enclave by the CPU access
> > > control.
> > >
> > > ... [ elided ] ..
> > > 
> > > The current implementation requires that the firmware sets
> > > IA32_SGXLEPUBKEYHASH* MSRs as writable so that ultimately the kernel can
> > > decide what enclaves it wants run. The implementation does not create
> > > any bottlenecks to support read-only MSRs later on.
> > 
> > It seems highly unlikely that a driver implementation with any type of
> > support for read-only launch control registers would ever get into the
> > kernel.  All one needs to do is review the conversations that Matthew
> > Garrett's lockdown patches engender to get a sense of that, ie:
> > 
> > https://lwn.net/Articles/818277/
> 
> We do not require read-only MSRs.

Greg is pointing out the opposite, that supporting read-only MSRs is highly
unlikely to ever be supported in the mainline kernel.