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

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Message-ID: <20200918232458.GA6175@linux.intel.com>
Date:   Sat, 19 Sep 2020 02:24:58 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, linux-sgx@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        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,
        Dave Hansen <dave.hansen@...el.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 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@...ux.intel.com> wrote:
> >
> > From: Sean Christopherson <sean.j.christopherson@...el.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