linux-kernel - Re: [PATCH v23 12/24] x86/sgx: Linux Enclave Driver

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Date:   Fri, 1 Nov 2019 13:16:59 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, nhorman@...hat.com, npmccallum@...hat.com,
        serge.ayoun@...el.com, shay.katz-zamir@...el.com,
        haitao.huang@...el.com, andriy.shevchenko@...ux.intel.com,
        tglx@...utronix.de, kai.svahn@...el.com, bp@...en8.de,
        josh@...htriplett.org, luto@...nel.org, kai.huang@...el.com,
        rientjes@...gle.com, cedric.xing@...el.com, puiterwijk@...hat.com,
        linux-security-module@...r.kernel.org,
        Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [PATCH v23 12/24] x86/sgx: Linux Enclave Driver

On 11/1/19 11:32 AM, Sean Christopherson wrote:
> On Fri, Nov 01, 2019 at 09:28:17AM -0400, Stephen Smalley wrote:
>> On 11/1/19 9:16 AM, Stephen Smalley wrote:
>>> So, IIUC, that means that merging the driver will create a regression with
>>> respect to LSM control over executable mappings that will only be
>>> rectified at some future point in time if/when someone submits LSM hooks
>>> or calls to existing hooks to restore such control.  That doesn't seem
>>> like a good idea.  Why can't you include at least that basic level of
>>> control now?  It is one thing to defer finer grained control or
>>> SGX-specific access controls to the future - that I can understand.  But
>>> introducing a regression in the existing controls is not really ok.
>>
>> Unless you are arguing that the existing checks on mmap/mprotect of
>> /dev/sgx/enclave are a coarse-grained approximation (effectively requiring
>> WX to the file or execmem for any user of SGX).
> 
> Yes, that's the argument as running any enclave will require RWX access to
> /dev/sgx/enclave.  EXECMEM won't trigger for SGX users as /dev/sgx/enclave
> must be MAP_SHARED and it's a non-private file (not backed by anonymous
> inode, in case I got the file terminology wrong).

Ok, so for SELinux's purposes, one will need to allow :file { open ioctl 
map read write execute } to whatever type is ultimately assigned to 
/dev/sgx/enclave in order to use SGX.