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Message-ID: <CA+icZUUp9rgx2Dvsww6QbTGRZz5=mf75D0_KncwdgCEZe01-EA@mail.gmail.com> Date: Sat, 21 Dec 2024 19:17:05 +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, xen-devel <xen-devel@...ts.xenproject.org> Subject: Re: [Linux-6.12.y] XEN: CVE-2024-53241 / XSA-466 and Clang-kCFI On Fri, Dec 20, 2024 at 2:39 AM Andrew Cooper <andrew.cooper3@...rix.com> wrote: > > On 20/12/2024 12:27 am, Sedat Dilek wrote: > > 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? > > Oh, that's distinctly less good. > > Start with just "example". It's literally a hello world microkernel, > but the symptoms you're seeing is a dom0 crash, so it will likely > provoke it. > > Do you have serial to the machine? If so, boot Xen with `console=com1 > com1=115200,8n1` (or com2, as appropriate). > > If not and you've only got a regular screen, boot Xen with `vga=,keep > noreboot` (comma is important) which might leave enough information on > screen to get an idea of what's going on. > YES # xl info | grep xen_commandline xen_commandline : placeholder vga=,keep noreboot > Full command line docs at > https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html > > > 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? > > No. XSA-466 is really "well don't do that then if it matters". > > More generally, not all XSAs are amenable to testing in this way. > > ~Andrew On Debian 6.12.6 kernel the TESTS stop with test-hvm64-xsa-454 - machine freezes - hard reboot. dileks@...za:~/src/xtf/git$ sudo ./xtf-runner -a --host root@...za:/var/log/xen# LC_ALL=C ls -alth | head -20 total 1.7M -rw-r--r-- 1 root adm 1008K Dec 21 19:10 xenstored-access.log drwxr-xr-x 16 root root 4.0K Dec 21 18:59 .. -rw-r--r-- 1 root adm 32 Dec 21 18:58 xenstored.log drwxr-s--- 2 root adm 36K Dec 21 18:58 . -rw-r--r-- 1 root adm 229 Dec 21 18:53 xl-test-hvm64-xsa-317.log -rw-r--r-- 1 root adm 67 Dec 21 18:53 xl-test-hvm64-xsa-454.log -rw-r--r-- 1 root adm 145 Dec 21 18:53 qemu-dm-test-hvm64-xsa-454.log -rw-r--r-- 1 root adm 232 Dec 21 18:53 qemu-dm-test-hvm64-xsa-451.log -rw-r--r-- 1 root adm 211 Dec 21 18:53 xl-test-hvm64-xsa-451.log -rw-r--r-- 1 root adm 232 Dec 21 18:53 xl-test-hvm32pse-xsa-317.log -rw-r--r-- 1 root adm 228 Dec 21 18:53 xl-test-pv64-xsa-444.log -rw-r--r-- 1 root adm 228 Dec 21 18:53 xl-test-pv64-xsa-339.log -rw-r--r-- 1 root adm 228 Dec 21 18:53 xl-test-pv64-xsa-333.log -rw-r--r-- 1 root adm 228 Dec 21 18:53 xl-test-pv64-xsa-317.log -rw-r--r-- 1 root adm 232 Dec 21 18:53 qemu-dm-test-hvm64-xsa-317.log -rw-r--r-- 1 root adm 232 Dec 21 18:53 xl-test-hvm32pae-xsa-317.log -rw-r--r-- 1 root adm 232 Dec 21 18:53 qemu-dm-test-hvm32pse-xsa-317.log -rw-r--r-- 1 root adm 229 Dec 21 18:53 xl-test-hvm32-xsa-317.log -rw-r--r-- 1 root adm 232 Dec 21 18:53 qemu-dm-test-hvm32pae-xsa-317.log root@...za:/var/log/xen# cat qemu-dm-test-hvm64-xsa-454.log VNC server running on 127.0.0.1:5900 xen-qemu-system-i386: failed to create 'console' device '0': declining to handle console type 'xenconsoled' root@...za:/var/log/xen# cat xl-test-hvm64-xsa-454.log Waiting for domain test-hvm64-xsa-454 (domid 94) to die [pid 4686] -Sedat-
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