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[92.26.98.202]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4366120088esm31993515e9.13.2024.12.19.17.39.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 17:39:08 -0800 (PST) Message-ID: <43166e29-ff2d-4a9d-8c1b-41b5e247974b@citrix.com> Date: Fri, 20 Dec 2024 01:39:07 +0000 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Linux-6.12.y] XEN: CVE-2024-53241 / XSA-466 and Clang-kCFI To: sedat.dilek@gmail.com Cc: Juergen Gross , Peter Zijlstra , Sami Tolvanen , Jan Beulich , Josh Poimboeuf , Linus Torvalds , Greg Kroah-Hartman , Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Kees Cook , Nathan Chancellor , llvm@lists.linux.dev, xen-devel References: <099d3a80-4fdb-49a7-9fd0-207d7386551f@citrix.com> <90640a5d-ff17-4555-adc6-ae9e21e24ebd@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 20/12/2024 12:27 am, Sedat Dilek wrote: > On Fri, Dec 20, 2024 at 12:26 AM Andrew Cooper > wrote: >> On 19/12/2024 11:10 pm, Sedat Dilek wrote: >>> On Thu, Dec 19, 2024 at 6:07 PM Sedat Dilek wrote: >>>> On Thu, Dec 19, 2024 at 5:44 PM Andrew Cooper 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. Full command line docs at https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html > dileks@iniza:~/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