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From: Ingo Molnar <mingo@kernel.org>
To: Khalid Aziz <khalid.aziz@oracle.com>
Cc: juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de,
	keescook@google.com, konrad.wilk@oracle.com,
	Juerg Haefliger <juerg.haefliger@canonical.com>,
	deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
	tyhicks@canonical.com, dwmw@amazon.co.uk,
	andrew.cooper3@citrix.com, jcm@redhat.com,
	boris.ostrovsky@oracle.com, iommu@lists.linux-foundation.org,
	x86@kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-security-module@vger.kernel.org,
	Khalid Aziz <khalid@gonehiking.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@kernel.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>
Subject: Re: [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame Ownership (XPFO)
Date: Wed, 17 Apr 2019 19:09:18 +0200
Message-ID: <20190417170918.GA68678@gmail.com> (raw)
In-Reply-To: <e16c1d73-d361-d9c7-5b8e-c495318c2509@oracle.com>


* Khalid Aziz <khalid.aziz@oracle.com> wrote:

> > I.e. the original motivation of the XPFO patches was to prevent execution 
> > of direct kernel mappings. Is this motivation still present if those 
> > mappings are non-executable?
> > 
> > (Sorry if this has been asked and answered in previous discussions.)
> 
> Hi Ingo,
> 
> That is a good question. Because of the cost of XPFO, we have to be very
> sure we need this protection. The paper from Vasileios, Michalis and
> Angelos - <http://www.cs.columbia.edu/~vpk/papers/ret2dir.sec14.pdf>,
> does go into how ret2dir attacks can bypass SMAP/SMEP in sections 6.1
> and 6.2.

So it would be nice if you could generally summarize external arguments 
when defending a patchset, instead of me having to dig through a PDF 
which not only causes me to spend time that you probably already spent 
reading that PDF, but I might also interpret it incorrectly. ;-)

The PDF you cited says this:

  "Unfortunately, as shown in Table 1, the W^X prop-erty is not enforced 
   in many platforms, including x86-64.  In our example, the content of 
   user address 0xBEEF000 is also accessible through kernel address 
   0xFFFF87FF9F080000 as plain, executable code."

Is this actually true of modern x86-64 kernels? We've locked down W^X 
protections in general.

I.e. this conclusion:

  "Therefore, by simply overwriting kfptr with 0xFFFF87FF9F080000 and 
   triggering the kernel to dereference it, an attacker can directly 
   execute shell code with kernel privileges."

... appears to be predicated on imperfect W^X protections on the x86-64 
kernel.

Do such holes exist on the latest x86-64 kernel? If yes, is there a 
reason to believe that these W^X holes cannot be fixed, or that any fix 
would be more expensive than XPFO?

Thanks,

	Ingo

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1554248001.git.khalid.aziz@oracle.com>
     [not found] ` <e6c57f675e5b53d4de266412aa526b7660c47918.1554248002.git.khalid.aziz@oracle.com>
     [not found]   ` <CALCETrXvwuwkVSJ+S5s7wTBkNNj3fRVxpx9BvsXWrT=3ZdRnCw@mail.gmail.com>
     [not found]     ` <20190404013956.GA3365@cisco>
     [not found]       ` <CALCETrVp37Xo3EMHkeedP1zxUMf9og=mceBa8c55e1F4G1DRSQ@mail.gmail.com>
     [not found]         ` <20190404154727.GA14030@cisco>
2019-04-04 16:23           ` [RFC PATCH v9 02/13] x86: always set IF before oopsing from page fault Sebastian Andrzej Siewior
2019-04-04 16:44 ` [RFC PATCH v9 00/13] Add support for eXclusive Page Frame Ownership Nadav Amit
2019-04-04 17:18   ` Khalid Aziz
     [not found] ` <f1ac3700970365fb979533294774af0b0dd84b3b.1554248002.git.khalid.aziz@oracle.com>
2019-04-17 16:15   ` [RFC PATCH v9 03/13] mm: Add support for eXclusive Page Frame Ownership (XPFO) Ingo Molnar
2019-04-17 16:49     ` Khalid Aziz
2019-04-17 17:09       ` Ingo Molnar [this message]
2019-04-17 17:19         ` Nadav Amit
2019-04-17 17:26           ` Ingo Molnar
2019-04-17 17:44             ` Nadav Amit
2019-04-17 21:19               ` Thomas Gleixner
     [not found]                 ` <CAHk-=wgBMg9P-nYQR2pS0XwVdikPCBqLsMFqR9nk=wSmAd4_5g@mail.gmail.com>
2019-04-17 23:42                   ` Thomas Gleixner
2019-04-17 23:52                     ` Linus Torvalds
2019-04-18  4:41                       ` Andy Lutomirski
2019-04-18  5:41                         ` Kees Cook
2019-04-18 14:34                           ` Khalid Aziz
2019-04-22 19:30                             ` Khalid Aziz
2019-04-22 22:23                             ` Kees Cook
2019-04-18  6:14                       ` Thomas Gleixner
2019-04-17 17:33         ` Khalid Aziz
2019-04-17 19:49           ` Andy Lutomirski
2019-04-17 19:52             ` Tycho Andersen
2019-04-17 20:12             ` Khalid Aziz
2019-05-01 14:49       ` Waiman Long
2019-05-01 15:18         ` Khalid Aziz

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