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Date:   Sat, 19 Sep 2020 02:24:58 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     X86 ML <x86@kernel.org>, linux-sgx@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Linux-MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Jethro Beekman <jethro@fortanix.com>,
        Darren Kenny <darren.kenny@oracle.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        asapek@google.com, Borislav Petkov <bp@alien8.de>,
        "Xing, Cedric" <cedric.xing@intel.com>, chenalexchen@google.com,
        Conrad Parker <conradparker@google.com>, cyhanish@google.com,
        Dave Hansen <dave.hansen@intel.com>,
        "Huang, Haitao" <haitao.huang@intel.com>,
        Josh Triplett <josh@joshtriplett.org>,
        "Huang, Kai" <kai.huang@intel.com>,
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        Christian Ludloff <ludloff@google.com>,
        Neil Horman <nhorman@redhat.com>,
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        Patrick Uiterwijk <puiterwijk@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Thomas Gleixner <tglx@linutronix.de>, yaozhangx@google.com
Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect()'
Message-ID: <20200918232458.GA6175@linux.intel.com>
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On Fri, Sep 18, 2020 at 08:09:04AM -0700, Andy Lutomirski wrote:
> On Tue, Sep 15, 2020 at 4:28 AM Jarkko Sakkinen
> <jarkko.sakkinen@linux.intel.com> wrote:
> >
> > From: Sean Christopherson <sean.j.christopherson@intel.com>
> >
> > Add vm_ops()->mprotect() for additional constraints for a VMA.
> >
> > Intel Software Guard eXtensions (SGX) will use this callback to add two
> > constraints:
> >
> > 1. Verify that the address range does not have holes: each page address
> >    must be filled with an enclave page.
> > 2. Verify that VMA permissions won't surpass the permissions of any enclave
> >    page within the address range. Enclave cryptographically sealed
> >    permissions for each page address that set the upper limit for possible
> >    VMA permissions. Not respecting this can cause #GP's to be emitted.
> 
> It's been awhile since I looked at this.  Can you remind us: is this
> just preventing userspace from shooting itself in the foot or is this
> something more important?
> 
> --Andy

Haitao found this:

https://patchwork.kernel.org/patch/10978327/

The way I understand it, for an LSM hook it makes sense that the
mprotect() can deduce a single permission for an enclave address range.
With those constraints it is possible.

/Jarkko