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References: <20200915112842.897265-1-jarkko.sakkinen@linux.intel.com> <20200915112842.897265-11-jarkko.sakkinen@linux.intel.com>
In-Reply-To: <20200915112842.897265-11-jarkko.sakkinen@linux.intel.com>
From:   Andy Lutomirski <luto@kernel.org>
Date:   Fri, 18 Sep 2020 08:09:04 -0700
Message-ID: <CALCETrX9T1ZUug=M5ba9g4H5B7kV=yL5RzuTaeAEdy3uAieN_A@mail.gmail.com>
Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect()
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
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>,
        "Svahn, Kai" <kai.svahn@intel.com>, Keith Moyer <kmoy@google.com>,
        Christian Ludloff <ludloff@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        Neil Horman <nhorman@redhat.com>,
        Nathaniel McCallum <npmccallum@redhat.com>,
        Patrick Uiterwijk <puiterwijk@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Thomas Gleixner <tglx@linutronix.de>, yaozhangx@google.com
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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