linux-kernel - Re: [PATCH v20 00/28] Intel SGX1 support

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Date:   Wed, 15 May 2019 12:58:40 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     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>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "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: [PATCH v20 00/28] Intel SGX1 support

On Wed, May 15, 2019 at 11:49:09AM +0300, Jarkko Sakkinen wrote:
> On Tue, May 14, 2019 at 08:13:36AM -0700, Andy Lutomirski wrote:
> > On Tue, May 14, 2019 at 3:43 AM Jarkko Sakkinen
> > <jarkko.sakkinen@...ux.intel.com> wrote:
> > >
> > > On Mon, May 13, 2019 at 01:29:26PM +0300, Jarkko Sakkinen wrote:
> > > > I did study through SDK's file format and realized that it does not
> > > > does make sense after all to embed one.
> > > >
> > > > To implement it properly you would probably need a new syscall (lets say
> > > > sgx_load_enclave) and also that enclaves are not just executables
> > > > binaries. It is hard to find a generic format for them as applications
> > > > range from simply protecting part of an application to running a
> > > > containter inside enclave.
> > >
> > > I'm still puzzling what kind of changes you were discussing considering
> > > SGX_IOC_ENCLAVE_ADD_PAGE.
> > 
> > I think it's as simple as requiring that, if SECINFO.X is set, then
> > the src pointer points to the appropriate number of bytes of
> > executable memory.  (Unless there's some way for an enclave to change
> > SECINFO after the fact -- is there?)  Sadly, we don't really have the
> > a nice in-kernel API for that right now.  You could do
> > down_read(mmap_sem) and find_vma().  Arguably there is no value to
> > checking that PKRU allows execute to the data.
> 
> OK, so you would actually go on to check whether the VMA where the data
> is copied contains executable data?
> 
> What if SECINFO.X is not set and you EADD to region that is executable
> in the enclave VMA? E.g. have RWX VMA for the enclave just to give a
> simple example. Then you could carry executable code in the data
> sections of the binary.

This would require to be done after the enclave is initialized of course
with EMODPR, which requires the enclave to accept the permission change
with EACCEPT, which limits somewhat. This means that the static enclave
would be fully covered.

/Jarkko