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

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Message-ID: <20190515132147.GA5875@linux.intel.com>
Date:   Wed, 15 May 2019 06:21:47 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        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: [PATCH v20 00/28] Intel SGX1 support

On Wed, May 15, 2019 at 01:35:31PM +0300, Jarkko Sakkinen wrote:
> On Tue, May 14, 2019 at 01:45:27PM -0700, Sean Christopherson wrote:
> > On Tue, May 14, 2019 at 08:13:36AM -0700, Andy Lutomirski wrote:
> > > 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?)
> > 
> > Nit: SECINFO is just the struct passed to EADD, I think what you're really
> > asking is "can the EPCM permissions be changed after the fact".
> > 
> > And the answer is, yes.
> > 
> > On SGX2 hardware, the enclave can extend the EPCM permissions at runtime
> > via ENCLU[EMODPE], e.g. to make a page writable.
> 
> Small correction: it is EMODPR.

No, I'm referring to EMODPE, note the ENCLU classification.

> Anyway, it is good to mention that these would require EACCEPT from the
> enclave side. In order to take advantage of this is in a malicous
> enclave, one would require SELinux/IMA/whatnot policy to have permitted
> it in the first place.

EMODPE doesn't require EACCEPT or any equivalent from the kernel.  As
you alluded to, the page tables would still need to allow PROT_EXEC.  I
was simply trying to answer Andy's question regarding SECINFO.

> Thus, it cannot be said that it breaks the security policy if this would
> happen because policy has allowed to use the particular enclave.