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

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Message-ID: <CA+icZUW-i53boHBPt+8zh-D921XFbPb_Kc=dzdgCK1QvkOgCsw@mail.gmail.com>
Date: Fri, 20 Dec 2024 00:10:08 +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 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.

Thanks.

Best regards,
-Sedat-

View attachment "xl-info.txt" of type "text/plain" (1382 bytes)

Download attachment "config-6.12.6-1-amd64-clang19-kcfi" of type "application/octet-stream" (281308 bytes)

View attachment "xl-dmesg_6.12.6-1-amd64-clang19-kcfi.txt" of type "text/plain" (16384 bytes)

View attachment "dmesg-T_6.12.6-1-amd64-clang19-kcfi.txt" of type "text/plain" (91020 bytes)

View attachment "xenstore-ls.txt" of type "text/plain" (1108 bytes)