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Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect()
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        linux-sgx@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        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,
        "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>,
        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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Message-ID: <25d46fdc-1c19-2de8-2ce8-1033a0027ecf@intel.com>
Date:   Tue, 22 Sep 2020 08:11:14 -0700
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On 9/22/20 5:58 AM, Jarkko Sakkinen wrote:
> Intel Sofware Guard eXtensions (SGX) allows creation of executable blobs
> called enclaves, of which page permissions are defined when the enclave

"of which" => "for which"

> is first loaded. Once an enclave is loaded and initialized, it can be
> mapped to the process address space.

Could you compare and contrast this a *bit* with existing executables?
What's special about SGX?  ELF executables have page permissions inside
the binary too.  Why don't we use this mechanism for them?

> Enclave permissions can be dynamically modified by using ENCLS[EMODPE]

I'm not sure this sentence matters.  I'm not sure why I care what the
instruction is named that does this.  But, it _sounds_ here like an
enclave can adjust its own permissions directly with ENCLS[EMODPE].

> instruction. We want to limit its use to not allow higher permissions than
> the ones defined when the enclave was first created.

Rather than higher and lower, please use stronger and weaker.

Also, please get rid of the "we".

> Add 'mprotect' hook to vm_ops, so that we can implement a callback for SGX
> that will check that {mmap, mprotect}() permissions do not surpass any of
> the page permissions in the address range defined.

"check" => "ensure"

> This is required in order to be able to make any access control decisions
> when enclave pages are loaded.
Now I'm confused.  I actually don't think I have a strong understanding
of how an enclave actually gets loaded, how mmap() and mprotect() are
normally used and what this hook is intended to thwart.