linux-kernel - Re: [RFC PATCH v2 2/5] x86/sgx: Require userspace to define enclave pages' protection bits

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Date:   Mon, 10 Jun 2019 18:27:17 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Cedric Xing <cedric.xing@...el.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        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,
        Jethro Beekman <jethro@...tanix.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, nhorman@...hat.com,
        npmccallum@...hat.com, Serge Ayoun <serge.ayoun@...el.com>,
        Shay Katz-zamir <shay.katz-zamir@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Kai Svahn <kai.svahn@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        Kai Huang <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        William Roberts <william.c.roberts@...el.com>,
        Philip Tricca <philip.b.tricca@...el.com>
Subject: Re: [RFC PATCH v2 2/5] x86/sgx: Require userspace to define enclave
 pages' protection bits

On Wed, Jun 05, 2019 at 07:11:42PM -0700, Sean Christopherson wrote:
> [SNAP]

Same general criticism as for the previous patch: try to say things as
they are without anything extra.

> A third alternative would be to pull the protection bits from the page's
> SECINFO, i.e. make decisions based on the protections enforced by
> hardware.  However, with SGX2, userspace can extend the hardware-
> enforced protections via ENCLU[EMODPE], e.g. can add a page as RW and
> later convert it to RX.  With SGX2, making a decision based on the
> initial protections would either create a security hole or force SGX to
> dynamically track "dirty" pages (see first alternative above).
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>

'flags' should would renamed as 'secinfo_flags_mask' even if the name is
longish. It would use the same values as the SECINFO flags. The field in
struct sgx_encl_page should have the same name. That would express
exactly relation between SECINFO and the new field. I would have never
asked on last iteration why SECINFO is not enough with a better naming.

The same field can be also used to cage page type to a subset of values.

/Jarkko