CVE-2022-42331

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2022-42331 / XSA-429 version 3 x86: speculative vulnerability in 32bit SYSCALL path UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= Due to an oversight in the very original Spectre/Meltdown security work (XSA-254), one entrypath performs its speculation-safety actions too late. In some configurations, there is an unprotected RET instruction which can be attacked with a variety of speculative attacks. IMPACT ====== An attacker might be able to infer the contents of arbitrary host memory, including memory assigned to other guests. VULNERABLE SYSTEMS ================== Xen versions 4.5 through 4.17 are vulnerable. Older versions are not vulnerable. Only x86 CPUs are potentially vulnerable. CPUs of other architectures are not vulnerable. The problematic codepath is only reachable on x86 CPUs which follow AMD’s behaviour with respect to SYSCALL instructions from compatibility mode segments. This means that AMD and Hygon CPUs are potentially vulnerable, whereas Intel CPUs are not. Other vendors have not been checked. Only PV guests can leverage the vulnerability. On Xen 4.16 and later, the vulnerability is only present if 32bit PV guest support is compiled in - i.e. CONFIG_PV32=y. On Xen 4.15 and older, all supported build configurations are vulnerable. The vulnerability is only present when booting on hardware that supports SMEP or SMAP (Supervisor Mode Execution/Access Prevention). This is believed to be some Family 0x16 models, and all later CPUs. MITIGATION ========== Not running untrusted PV guests will avoid the issue. CREDITS ======= This issue was discovered by Andrew Cooper of XenServer. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. Note that patches for released versions are generally prepared to apply to the stable branches, and may not apply cleanly to the most recent release tarball. Downstreams are encouraged to update to the tip of the stable branch before applying these patches. xsa429.patch xen-unstable - Xen 4.16 xsa429-4.15.patch Xen 4.15 - Xen 4.14 $ sha256sum xsa429* 2d7be90d917c475ab5217e657d2b44f5d8b107d9023dca034fcfb7feab07b2f0 xsa429.meta 36ed36dbfaad9e5df5fa87b9a3d9e9c531f476f97eeb2afe280aa238032a0540 xsa429.patch 7ac3d4182585e5d2d39231f10e7c0c9fcb972c82cf81cb884e95b628187de3a7 xsa429-4.15.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches and/or mitigations described above (or others which are substantially similar) is permitted during the embargo, even on public-facing systems with untrusted guest users and administrators. But: Distribution of updated software is prohibited (except to other members of the predisclosure list). Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team. (Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team’s decisionmaking.) For more information about permissible uses of embargoed information, consult the Xen Project community’s agreed Security Policy: http://www.xenproject.org/security-policy.html -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmQZlWMMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZil4H/2b1DkLLz4RQqAgvaB8+SBeVLPqoZ7QxGLl8QXWT AMjFdy+M5T1OtbrMvEYCZNYhZnGOJgmVagERUvg/yZbPYx28NIHjG4+u90Ot6OId AQPqdrJ0wjEzN/ppNpnu1ALofAGbjsnAypEouGPh12gh5fcpcLQdT0rvpl2ff5f6 Qi4ShtUXhBiduBQcJ0TSneSCf5s7cq1+sMenntenK5Nrsvg7gu51YR45FyKyXdZc raonkGDny9kmDAjdKkywS2Au2763ph9nHbW5TbD17s65AKUDTupzk+QlFPhJLIP+ /gxDoUjKFiD/eY0AABWMAFGGvHFRNvdhTfUd6ImmWhqdEeE= =HxUJ -----END PGP SIGNATURE-----