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

[Sean Christopherson]

On Wed, Jun 05, 2019 at 06:10:18PM +0300, Jarkko Sakkinen wrote:
> 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 at linux.intel.com> 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 at intel.com>
> > >
> > > 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.
> 
> Not exactly sure why using it to pass the RWX bits to EADD ioctl would
> cause anything to SGX2 support.

Andy was pointing out that with SGX2 the enclave can do ENCLU[EMODPE] to
make the page executable, e.g. add the page with SECINFO.R and then
mprotect() the enclave VMA (whose vm_file == /dev/sgx/enclave) PROT_EXEC.
We could hard enforce SECINFO, i.e. set the enclave page's protection bits
directly from SECINFO, but that would neuter SGX2, e.g. would break
converting RW to RX.