Re: [RFC PATCH 7/9] x86/sgx: Enforce noexec filesystem restriction for enclaves

From: Sean Christopherson
Date: Tue Jun 04 2019 - 16:38:44 EST

On Tue, Jun 04, 2019 at 01:25:10PM -0700, Andy Lutomirski wrote:
> On Tue, Jun 4, 2019 at 9:26 AM Jarkko Sakkinen
> <jarkko.sakkinen@xxxxxxxxxxxxxxx> wrote:
> >
> > On Fri, May 31, 2019 at 04:31:57PM -0700, Sean Christopherson wrote:
> > > Do not allow an enclave page to be mapped with PROT_EXEC if the source
> > > page is backed by a file on a noexec file system.
> > >
> > > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> >
> > Why don't you just check in sgx_encl_add_page() that whether the path
> > comes from noexec and deny if SECINFO contains X?
> >
> SECINFO seems almost entirely useless for this kind of thing because
> of SGX2. I'm thinking that SECINFO should be completely ignored for
> anything other than its required architectural purpose.


I've already (somewhat unknowingly) reworked the SELinux patch such that
it ignores @prot (the SECINFO protections) and only looks at @allowed_prot
(the declared protections). If the kernel ignores SECINFO protections
entirely then the LSM hook can simply be:

int selinux_enclave_load(struct vm_area_struct *vma, unsigned long prot)

I.e. LSMs can be blissfully unaware that @prot isn't technically what's
going into the PTEs *now*.