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

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Date:   Tue, 4 Jun 2019 00:05:34 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        William Roberts <bill.c.roberts@...il.com>,
        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>,
        Eric Paris <eparis@...isplace.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        Jethro Beekman <jethro@...tanix.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 Thu, May 30, 2019 at 11:01:10AM -0700, Sean Christopherson wrote:
>   - Requires enclave builder to mark enclave pages executable in the
>     non-enclave VMAs, which may unnecessarily require EXECMOD on the
>     source file, or even worse, EXECMEM, and potentially increases the
>     attack surface since the file must be executable.

Enclave builder marks *non-enclave pages*? Not following.

> W^X handling:
>   - mmap() to /dev/sgx/enclave only allowed with PROT_NONE, i.e. force
>     userspace through mprotect() to simplify the kernel implementation.
>   - Add vm_ops mprotect() ops hook (I'll refer to SGX's implementation
>     as SGX.mprotect())
>   - Take explicit ALLOW_WRITE at ADD_REGION, a.k.a. EADD
>   - ADD_REGION also used to describe EAUG region (tentatively for SGX2).
>   - Track "can be written at some point in time (past or future)" as
>     ALLOW_WRITE (to avoid confusiong with MAY_WRITE).  A priori knowledge
>     of writability avoids having to track/coordinate PROT_WRITE across
>     VMAs and MMs.

Still not sure why you want to use vm_ops instead of file_operations.

The approach I've been proposing earlier in this email thread before
these new proposals can be summarized from hook perspective as:

- Allow mmap() only before ECREATE and require it to be size
  of the ELRANGE (ECREATE ioctl would check this). This would
  be with PROT_NONE.
- Disallow mprotect() before EINIT. Requires a new callback
  to file_operations like mmap() has.
- After EINIT check for each mprotect() that it matches the
  permissions of underlying enclave pages. Disallow mmap()
  after EINIT.

/Jarkko