linux-kernel - Re: [PATCH v38 10/24] mm: Add vm

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Message-ID: <20201027004048.GC28122@linux.intel.com>
Date:   Mon, 26 Oct 2020 17:40:49 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     "Dr. Greg" <greg@...ellic.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jethro Beekman <jethro@...tanix.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asapek@...gle.com, Borislav Petkov <bp@...en8.de>,
        "Xing, Cedric" <cedric.xing@...el.com>, chenalexchen@...gle.com,
        Conrad Parker <conradparker@...gle.com>, cyhanish@...gle.com,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Keith Moyer <kmoy@...gle.com>,
        Christian Ludloff <ludloff@...gle.com>,
        Neil Horman <nhorman@...hat.com>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        Patrick Uiterwijk <puiterwijk@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, yaozhangx@...gle.com
Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect()

On Mon, Oct 26, 2020 at 03:59:35PM -0700, Andy Lutomirski wrote:
> > On Oct 26, 2020, at 3:51 AM, Dr. Greg <greg@...ellic.com> wrote:
> > The open question in all of this is that the EDMM paper, as well as
> > the SDM, indicate the effects of an ENCLU[EMODPE] are immediate inside
> > of a running enclave.  I'm assuming that this does NOT mean that once
> > a context of execution is running in enclave mode it would be capable
> > of evading standard page protections but the 'immediate' is somewhat
> > disquieting and probably deserves clarification, despite Dave Hansen's
> > adament concerns about discussing the instruction... :-)
> 
> If EMODPE writes an entry into the TLB that violates PTE permissions, then we
> have a real problem. I would be very surprised if this were to be the case.

EMODPE only affects the EPCM, it doesn't magically change the PTEs or insert
into the TLB.  The "immediate" wording in the whitepaper is differentiating it
from EMODPR and EMODT, where the modifications only take effect after they have
been verified by the enclave via EACCEPT.