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Date:   Thu, 30 May 2019 14:16:45 -0700
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Stephen Smalley <sds@tycho.nsa.gov>,
        "Xing, Cedric" <cedric.xing@intel.com>,
        William Roberts <bill.c.roberts@gmail.com>,
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        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        Paul Moore <paul@paul-moore.com>,
        Eric Paris <eparis@parisplace.org>,
        "selinux@vger.kernel.org" <selinux@vger.kernel.org>,
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        "Dr. Greg" <greg@enjellic.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        David Rientjes <rientjes@google.com>
Subject: Re: SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)
Message-ID: <20190530211645.GB27551@linux.intel.com>
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On Thu, May 30, 2019 at 12:20:45PM -0700, Andy Lutomirski wrote:
> On Thu, May 30, 2019 at 11:01 AM Sean Christopherson
> <sean.j.christopherson@intel.com> wrote:
> >
> > On Thu, May 30, 2019 at 09:14:10AM -0700, Andy Lutomirski wrote:
> > > Enclave file -- that is, the file backing the vma from which the data is loaded.
> >
> > It wasn't explicitly called out in Andy's proposal(s), but the idea is
> > that the SGX driver would effectively inherit permissions from the source
> > VMA (EADD needs a source for the initial value of the encave page).
> 
> I actually meant for it to *not* work like this.  I don't want the
> source VMA to have to be VM_EXEC.  I think the LSM should just check
> permissions on ->vm_file.

But if ->vm_file is NULL, i.e. the enclave is not backed by a file,
then PROCESS__EXECMEM is required (or more likely, ENCLAVE__EXECMEM).

In practice, it's the same net effect of using sigstruct as a proxy,
i.e. *something* has to get to the file system to avoid EXECMEM.  But
putting the entire enclave to the filesystem seems like a heaver lift
than dumping the sigstruct.

And if sigstruct needs to be in the file system for
security_enclave_create/init()...