CVE-2022-26356

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2022-26356 / XSA-397 version 2 Racy interactions between dirty vram tracking and paging log dirty hypercalls UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= Activation of log dirty mode done by XEN_DMOP_track_dirty_vram (was named HVMOP_track_dirty_vram before Xen 4.9) is racy with ongoing log dirty hypercalls. A suitably timed call to XEN_DMOP_track_dirty_vram can enable log dirty while another CPU is still in the process of tearing down the structures related to a previously enabled log dirty mode (XEN_DOMCTL_SHADOW_OP_OFF). This is due to lack of mutually exclusive locking between both operations and can lead to entries being added in already freed slots, resulting in a memory leak. IMPACT ====== An attacker can cause Xen to leak memory, eventually leading to a Denial of Service (DoS) affecting the entire host. VULNERABLE SYSTEMS ================== All Xen versions from at least 4.0 onwards are vulnerable. Only x86 systems are vulnerable. Arm systems are not vulnerable. Only domains controlling an x86 HVM guest using Hardware Assisted Paging (HAP) can leverage the vulnerability. On common deployments this is limited to domains that run device models on behalf of guests. MITIGATION ========== Using only PV or PVH guests and/or running HVM guests in shadow mode will avoid the vulnerability. CREDITS ======= This issue was discovered by Roger Pau Monné of Citrix. 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. xsa397.patch xen-unstable xsa397-4.16.patch Xen 4.16.x - Xen 4.15.x xsa397-4.14.patch Xen 4.14.x - Xen 4.13.x xsa397-4.12.patch Xen 4.12.x $ sha256sum xsa397* 49c663e2bb9131dbc2488e12487f79bdf0dafd51a32413cbf3964e39d8779cae xsa397.patch 24f95f47b79739c9cb5b9110137c802989356c82d0aa27963b5ac7e33f667285 xsa397-4.12.patch 9af14f90ba10d074425eb6072a6c648082c92c1cf8b6f881f57ed2fc13d6e49d xsa397-4.14.patch ff5dd3b7a8dbf349c3b832b7916322c0296fa59c7f9cd2ba30858989add5f65c xsa397-4.16.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches 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 (except to other members of the predisclosure list) or deployment of mitigations is prohibited. 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/4UyVfoK9kFAmJMJDEMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZOUMH/RRZ8aMaoywqTV38SeTFne2tFT5jnWPPXR1ZGCvh 825hmSqzcYUaILbWFruUfT2PdpGoU9Eprz3xWXBDwgsUEGvKt7ZhGoWvxzXASlDh cPRh/XwQVEEYsB1cRSk/GoLxLCQEV8oGNpmAcjEM4K1dG0VbVaRD0W2thNCmyPcv d7aTkAdD2IE8NU4hX8YGN6v+UCkjrgzL0AF/hff9CMj7Sn/wBRrdStLT0LDZU20c G/5+9nsOAVM7EwrzImI5Lx9KELyHwl37XUPffbftyTLUofdHJ5PK40J1tNIRS/RW YYvs2alF7ng7LlwB/Go8gtn4XRx6xZidceYrUk22oB4JBqo= =Fje3 -----END PGP SIGNATURE-----