From: Ingo Molnar <mingo@kernel.org>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>,
juergh@gmail.com, Tycho Andersen <tycho@tycho.ws>,
jsteckli@amazon.de, keescook@google.com,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Juerg Haefliger <juerg.haefliger@canonical.com>,
deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
tyhicks@canonical.com, David Woodhouse <dwmw@amazon.co.uk>,
Andrew Cooper <andrew.cooper3@citrix.com>,
jcm@redhat.com, Boris Ostrovsky <boris.ostrovsky@oracle.com>,
iommu <iommu@lists.linux-foundation.org>, X86 ML <x86@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>,
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 19:26:32 +0200 [thread overview]
Message-ID: <20190417172632.GA95485@gmail.com> (raw)
In-Reply-To: <56A175F6-E5DA-4BBD-B244-53B786F27B7F@gmail.com>
* Nadav Amit <nadav.amit@gmail.com> wrote:
> > On Apr 17, 2019, at 10:09 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> >
> > * 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.
>
> As I was curious, I looked at the paper. Here is a quote from it:
>
> "In x86-64, however, the permissions of physmap are not in sane state.
> Kernels up to v3.8.13 violate the W^X property by mapping the entire region
> as “readable, writeable, and executable” (RWX)—only very recent kernels
> (≥v3.9) use the more conservative RW mapping.”
But v3.8.13 is a 5+ years old kernel, it doesn't count as a "modern"
kernel in any sense of the word. For any proposed patchset with
significant complexity and non-trivial costs the benchmark version
threshold is the "current upstream kernel".
So does that quote address my followup questions:
> 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?
?
What you are proposing here is a XPFO patch-set against recent kernels
with significant runtime overhead, so my questions about the W^X holes
are warranted.
Thanks,
Ingo
next prev parent reply other threads:[~2019-04-17 17:26 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1554248001.git.khalid.aziz@oracle.com>
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
2019-04-17 17:19 ` Nadav Amit
2019-04-17 17:26 ` Ingo Molnar [this message]
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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