Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame
 Ownership (XPFO)
From:   Khalid Aziz <khalid.aziz@oracle.com>
To:     Kees Cook <keescook@google.com>, Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Nadav Amit <nadav.amit@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Juerg Haefliger <juergh@gmail.com>,
        Tycho Andersen <tycho@tycho.ws>,
        Julian Stecklina <jsteckli@amazon.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        deepa.srinivasan@oracle.com, chris hyser <chris.hyser@oracle.com>,
        Tyler Hicks <tyhicks@canonical.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Jon Masters <jcm@redhat.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        iommu <iommu@lists.linux-foundation.org>,
        X86 ML <x86@kernel.org>,
        "linux-alpha@vger.kernel.org" <linux-arm-kernel@lists.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        Khalid Aziz <khalid@gonehiking.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Dave Hansen <dave@sr71.net>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Arjan van de Ven <arjan@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <cover.1554248001.git.khalid.aziz@oracle.com>
 <f1ac3700970365fb979533294774af0b0dd84b3b.1554248002.git.khalid.aziz@oracle.com>
 <20190417161042.GA43453@gmail.com>
 <e16c1d73-d361-d9c7-5b8e-c495318c2509@oracle.com>
 <20190417170918.GA68678@gmail.com>
 <56A175F6-E5DA-4BBD-B244-53B786F27B7F@gmail.com>
 <20190417172632.GA95485@gmail.com>
 <063753CC-5D83-4789-B594-019048DE22D9@gmail.com>
 <alpine.DEB.2.21.1904172317460.3174@nanos.tec.linutronix.de>
 <CAHk-=wgBMg9P-nYQR2pS0XwVdikPCBqLsMFqR9nk=wSmAd4_5g@mail.gmail.com>
 <alpine.DEB.2.21.1904180129000.3174@nanos.tec.linutronix.de>
 <CAHk-=whUwOjFW6RjHVM8kNOv1QVLJuHj2Dda0=mpLPdJ1UyatQ@mail.gmail.com>
 <CALCETrXm9PuUTEEmzA8bQJmg=PHC_2XSywECittVhXbMJS1rSA@mail.gmail.com>
 <CAGXu5jL-qJtW7eH8S2yhqciE+J+FWz8HHzTrGJTgVUbd55n6dQ@mail.gmail.com>
 <8f9d059d-e720-cd24-faa6-45493fc012e0@oracle.com>
Organization: Oracle Corp
Message-ID: <302e3d5b-d2fd-3c25-335b-466ba83035c5@oracle.com>
Date:   Mon, 22 Apr 2019 13:30:41 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.5.1
MIME-Version: 1.0
In-Reply-To: <8f9d059d-e720-cd24-faa6-45493fc012e0@oracle.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 4/18/19 8:34 AM, Khalid Aziz wrote:
> On 4/17/19 11:41 PM, Kees Cook wrote:
>> On Wed, Apr 17, 2019 at 11:41 PM Andy Lutomirski <luto@kernel.org> wro=
te:
>>> I don't think this type of NX goof was ever the argument for XPFO.
>>> The main argument I've heard is that a malicious user program writes =
a
>>> ROP payload into user memory (regular anonymous user memory) and then=

>>> gets the kernel to erroneously set RSP (*not* RIP) to point there.
>>
>> Well, more than just ROP. Any of the various attack primitives. The NX=

>> stuff is about moving RIP: SMEP-bypassing. But there is still basic
>> SMAP-bypassing for putting a malicious structure in userspace and
>> having the kernel access it via the linear mapping, etc.
>>
>>> I find this argument fairly weak for a couple reasons.  First, if
>>> we're worried about this, let's do in-kernel CFI, not XPFO, to
>>
>> CFI is getting much closer. Getting the kernel happy under Clang, LTO,=

>> and CFI is under active development. (It's functional for arm64
>> already, and pieces have been getting upstreamed.)
>>
>=20
> CFI theoretically offers protection with fairly low overhead. I have no=
t
> played much with CFI in clang. I agree with Linus that probability of
> bugs in XPFO implementation itself is a cause of concern. If CFI in
> Clang can provide us the same level of protection as XPFO does, I
> wouldn't want to push for an expensive change like XPFO.
>=20
> If Clang/CFI can't get us there for extended period of time, does it
> make sense to continue to poke at XPFO?

Any feedback on continued effort on XPFO? If it makes sense to have XPFO
available as a solution for ret2dir issue in case Clang/CFI does not
work out, I will continue to refine it.

--
Khalid