oss-sec mailing list archives
Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak
From: Demi Marie Obenour <demi () invisiblethingslab com>
Date: Tue, 26 Sep 2023 21:59:19 -0400
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On Mon, Sep 25, 2023 at 04:05:37PM +0000, Xen Security wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2023-20588 / XSA-439 x86/AMD: Divide speculative information leak ISSUE DESCRIPTION ================= In the Zen1 microarchitecure, there is one divider in the pipeline which services uops from both threads. In the case of #DE, the latched result from the previous DIV to execute will be forwarded speculatively. This is a covert channel that allows two threads to communicate without any system calls. In also allows userspace to obtain the result of the most recent DIV instruction executed (even speculatively) in the core, which can be from a higher privilege context. For more information, see: * https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7008.html IMPACT ====== An attacker might be able to infer data from a different execution context on the same CPU core. VULNERABLE SYSTEMS ================== All versions of Xen are vulnerable. Only AMD Zen1 CPUs are believed to be vulnerable. MITIGATION ========== There is no mitigation. RESOLUTION ========== The patches for Xen overwrite the buffer in the divider on the return-to-guest path. However, as with some prior speculative vulnerabilities, the fix is only effective in combination with disabling SMT. For the same reasons as before, Xen does not disable SMT by default. The system administrator is required to risk-assess their workload, and choose whether to enable or disable SMT. Xen will issue a warning if SMT is active and the user has not provided an explicit choice via the smt=<bool> command line option. Details of the vulnerability became public before the Xen patches were complete. Hence the patches are already applied to the appropriate trees. They are: Xen-unstable: 1c18d7377453^..b5926c6ecf05 Xen 4.17: d2d2dcae879c^..9ac2f49f5fa3 Xen 4.16: 08539e8315fd^..de751c3d906d Xen 4.15: db3386e6cad6^..d7b78041dc81 -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmURr2UMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZA1QH/RNSR1O6QJjd7z2gSGA9Yka7VWyYOMB2J01AaIl7 69zCRkpqg+baF1aQaAVR0fj39aF7M7xXrd/LSk+E4BBiCRSxxRzbWUGYn9qTLR9w srbpGXqy0aWod9MiwfbTuEzf9uG8XpwOGoRg6p6YBRYE3WrQxIVnYY+KjeeToTEs +UXZ0iZPrjaGaqKnF+PpkX4CMsqHhxk3iJw+ZFX2V4fVNRYgCOpjejmMjbWM4ABr eSsCjTU92/YZvFOsTeIzu74h5yM6SH+XTPW2S8Ve5j3mk7sM8nIiYbIyTMWNCJID HXeodt6eHjhZzV2z7f+/zEngnoITIqz+X3tRcTkHB9+H5jU= =AtsG -----END PGP SIGNATURE-----
These detailed security advisories are one of the things I love about Xen. It's hard to trust a hypervisor (KVM) that will not issue them, for then one has no way to know if a particular problem got fixed. I'm CCing KVM here to make sure they have a fix. From their Git commit history, I am almost certain that seL4 does not. I'm CCing the seL4 developers to alert them of this and suggest that the x86 port be removed or at least have a big warning. - -- Sincerely, Demi Marie Obenour (she/her/hers) Invisible Things Lab -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEEdodNnxM2uiJZBxxxsoi1X/+cIsEFAmUTjHcACgkQsoi1X/+c IsH6/w//RbvVlls3bC5IUSv+cB3e8aQmiFOuosxycKki3PjMeHD/nmTnlQIZteQU EXRJRilEIfI8QsDiHKXtLz/gv9oDAvPKoUnqvdoRp9XKtUJ/USueDfujtWXSZB92 yhXMvCQ7m8Jaz0am7MbVBnZP3l2MTopHXxTe9ukeBJ2OAbGPFpjgv5d7uBpjmfTb vb2YE8fL1iS2hK1njBWifL+Ss70JNlSfIHBHRVMtNZg6xyC0B7fW7PPtXHWfVjMd PR6huOFg1v504ijacOYYW0eWjUv2aaURsKKAJaw5OnxbLzv6m+AxNBVAnss00PH7 B8KxhCNFOliGIm0Ih2S4F7EXFIYBQlzzAp1M95qzgY6FEurBasQ7OAQcsOFx1yae UCm56PCZcoQhEKDbA96zJhxi1E320W5MMQeYm3ByB1/jCRQxq+4gRVUp2T00tFAu C/LwdQJ5p5iHqhtZ9Y6YceA7OPbU+N4NhHC8azKj7gDvkpAYWrq1LzQrGaGE65Ax Th8BdD06iMK4ZZljl1MwkwLrZw3PMOpNz6I2YKQ/NktDGIDDIDDYQXCsoRb2Z+NU ZFAyaj5aUKMQCvzya+MYXP48r+CQl3nl4jLr6Fa0yEvn1ouWEByYuPOWR4JuyZI/ WtNSpCHRoyqX7SF60FWM5yDGCwJ07eJrmzIKWje6uthjmqjDmFc= =WiIH -----END PGP SIGNATURE-----
Current thread:
- Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Xen . org security team (Sep 25)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Solar Designer (Sep 25)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Andrew Cooper (Sep 25)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Solar Designer (Sep 25)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Andrew Cooper (Sep 26)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Solar Designer (Sep 26)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Andrew Cooper (Sep 26)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Andrew Cooper (Sep 25)
- Re: Xen Security Advisory 439 v1 (CVE-2023-20588) - x86/AMD: Divide speculative information leak Solar Designer (Sep 25)