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Date:   Wed, 15 May 2019 20:19:04 -0500
From:   "Haitao Huang" <haitao.huang@...ux.intel.com>
To:     "Andy Lutomirski" <luto@...nel.org>,
        "Sean Christopherson" <sean.j.christopherson@...el.com>
Cc:     "James Morris" <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "LSM List" <linux-security-module@...r.kernel.org>,
        "Paul Moore" <paul@...l-moore.com>,
        "Stephen Smalley" <sds@...ho.nsa.gov>,
        "Eric Paris" <eparis@...isplace.org>, selinux@...r.kernel.org,
        "Jarkko Sakkinen" <jarkko.sakkinen@...ux.intel.com>,
        "Jethro Beekman" <jethro@...tanix.com>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Dr. Greg" <greg@...ellic.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, "X86 ML" <x86@...nel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        "Svahn, Kai" <kai.svahn@...el.com>,
        "Borislav Petkov" <bp@...en8.de>,
        "Josh Triplett" <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "David Rientjes" <rientjes@...gle.com>
Subject: Re: SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)

On Wed, 15 May 2019 16:38:58 -0500, Sean Christopherson  
<sean.j.christopherson@...el.com> wrote:

> On Wed, May 15, 2019 at 11:27:04AM -0700, Andy Lutomirski wrote:
>> 2) Just like any other DSO, there are potential issues with how
>> enclaves deal with writable vs executable memory.  This takes two
>> forms.  First, a task should probably require EXECMEM, EXECMOD, or
>> similar permission to run an enclave that can modify its own text.
>> Second, it would be nice if a task that did *not* have EXECMEM,
>> EXECMOD, or similar could still run the enclave if it had EXECUTE
>> permission on the file containing the enclave.
>>
>> Currently, this all works because DSOs are run by mmapping the file to
>> create multiple VMAs, some of which are executable, non-writable, and
>> non-CoWed, and some of which are writable but not executable.  With
>> SGX, there's only really one inode per enclave (the anon_inode that
>> comes form /dev/sgx/enclave), and it can only be sensibly mapped
>> MAP_SHARED.
>
> I was wrong when I said /dev/sgx/enclave creates and returns an anon
> inode.  I was thinking of the KVM model for creating VMs.  SGX creates
> an enclave when /dev/sgx/enclave is opened and associates the enclave
> with the newly opened /dev/sgx/enclave fd.
>
> Regardless, the fundamental problem remains, mmap() of EPC works on a
> single inode.

If I read code in file_map_prot_check() correctly, only when you request  
W+X at the same time that EXECMEM would be required for MAP_SHARED, right?
If so, I believe SGX enclaves would never need that.

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