linux-kernel - Re: SGX vs LSM (Re: [PATCH v20 00/28] Intel SGX1 support)

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Message-ID: <20190515213858.GG5875@linux.intel.com>
Date:   Wed, 15 May 2019 14:38:58 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
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, 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.