linux-kernel - Re: [Linux-6.12.y] XEN: CVE-2024-53241 / XSA-466 and Clang-kCFI

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Message-ID: <CA+icZUVo69swc9QfwJr+mDuHqJKcFUexc08voP2O41g31HGx5w@mail.gmail.com>
Date: Fri, 20 Dec 2024 01:27:24 +0100
From: Sedat Dilek <sedat.dilek@...il.com>
To: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Juergen Gross <jgross@...e.com>, Peter Zijlstra <peterz@...radead.org>, 
	Sami Tolvanen <samitolvanen@...gle.com>, Jan Beulich <jbeulich@...e.com>, 
	Josh Poimboeuf <jpoimboe@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Sasha Levin <sashal@...nel.org>, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	Kees Cook <kees@...nel.org>, Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev
Subject: Re: [Linux-6.12.y] XEN: CVE-2024-53241 / XSA-466 and Clang-kCFI

On Fri, Dec 20, 2024 at 12:26 AM Andrew Cooper
<andrew.cooper3@...rix.com> wrote:
>
> On 19/12/2024 11:10 pm, Sedat Dilek wrote:
> > On Thu, Dec 19, 2024 at 6:07 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> >> On Thu, Dec 19, 2024 at 5:44 PM Andrew Cooper <andrew.cooper3@...rix.com> wrote:
> >>> On 19/12/2024 4:14 pm, Sedat Dilek wrote:
> >>>> Hi,
> >>>>
> >>>> Linux v6.12.6 will include XEN CVE fixes from mainline.
> >>>>
> >>>> Here, I use Debian/unstable AMD64 and the SLIM LLVM toolchain 19.1.x
> >>>> from kernel.org.
> >>>>
> >>>> What does it mean in ISSUE DESCRIPTION...
> >>>>
> >>>> Furthermore, the hypercall page has no provision for Control-flow
> >>>> Integrity schemes (e.g. kCFI/CET-IBT/FineIBT), and will simply
> >>>> malfunction in such configurations.
> >>>>
> >>>> ...when someone uses Clang-kCFI?
> >>> The hypercall page has functions of the form:
> >>>
> >>>     MOV $x, %eax
> >>>     VMCALL / VMMCALL / SYSCALL
> >>>     RET
> >>>
> >>> There are no ENDBR instructions, and no prologue/epilogue for hash-based
> >>> CFI schemes.
> >>>
> >>> This is because it's code provided by Xen, not code provided by Linux.
> >>>
> >>> The absence of ENDBR instructions will yield #CP when CET-IBT is active,
> >>> and the absence of hash prologue/epilogue lets the function be used in a
> >>> type-confused manor that CFI should have caught.
> >>>
> >>> ~Andrew
> >> Thanks for the technical explanation, Andrew.
> >>
> >> Hope that helps the folks of "CLANG CONTROL FLOW INTEGRITY SUPPORT".
> >>
> >> I am not an active user of XEN in the Linux-kernel but I am willing to
> >> test when Linux v6.12.6 is officially released and give feedback.
> >>
> > https://wiki.xenproject.org/wiki/Testing_Xen#Presence_test
> > https://wiki.xenproject.org/wiki/Testing_Xen#Commands_for_presence_testing
> >
> > # apt install -t unstable xen-utils-4.17 -y
> >
> > # xl list
> > Name                                        ID   Mem VCPUs      State   Time(s)
> > Domain-0                                     0  7872     4     r-----     398.2
> >
> > Some basic tests LGTM - see also attached stuff.
> >
> > If you have any tests to recommend, let me know.
>
> That itself is good enough as a smoke test.  Thankyou for trying it out.
>
> If you want something a bit more thorough, try
> https://xenbits.xen.org/docs/xtf/  (Xen's self-tests)
>
> Grab and build it, and `./xtf-runner -aqq --host` will run a variety of
> extra codepaths in dom0, without the effort of making/running full guests.
>
> ~Andrew

Run on Debian 6.12.5 and my selfmade 6.12.5 and 6.12.6.
All tests lead to a reboot in case of Debian or in my kernels to a shutdown.

Can you recommend a specific test?

dileks@...za:~/src/xtf/git$ sudo ./xtf-runner --list functional xsa | grep xsa-4
test-pv64-xsa-444
test-hvm64-xsa-451
test-hvm64-xsa-454

Is there no xsa-466 test?

Thanks.

BR,
-Sedat-