Date: Wed, 30 Apr 2014 12:16:18 +0000 From: Xen.org security team <security@....org> To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, xen-users@...ts.xen.org, oss-security@...ts.openwall.com CC: Xen.org security team <security@....org> Subject: Xen Security Advisory 91 - Hardware timer context is not properly context switched on ARM -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory XSA-91 version 2 Hardware timer context is not properly context switched on ARM UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= When running on an ARM platform Xen was not context switching the CNTKCTL_EL1 register, which is used by the guest kernel to control access by userspace processes to the hardware timers. This meant that any guest can reconfigure these settings for the entire system. IMPACT ====== A malicious guest kernel can reconfigure CNTKCTL_EL1 to block userspace access to the timer hardware for all domains, including control domains. Depending on the other guest kernels in use this may cause an unexpected exception in those guests which may lead to a kernel crash and therefore a denial of service. 64-bit ARM Linux is known to be susceptible to crashing in this way. A malicious guest kernel can also enable userspace access to the timer control registers, which may not be expected by kernels running in other domains. This can allow user processes to reprogram timer interrupts and therefore lead to unexpected behaviour, potentially up to and including crashing the guest. Userspace processes will also be able to read the current timestamp value for the domain perhaps leaking information to those processes. VULNERABLE SYSTEMS ================== Both 32- and 64-bit ARM systems are vulnerable from Xen 4.4 onwards. x86 systems are not vulnerable. MITIGATION ========== None. CREDITS ======= Chen Baozi discovered this issue as a bug which was then diagnosed by Julien Grall. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa91-unstable.patch xen-unstable xsa91-4.4.patch Xen 4.4.x $ sha256sum xsa91*.patch 8a3dc1f001274550acfe929a0a443b09f8164001f6eea76821bd87292b8732e0 xsa91-4.4.patch 327ccd88f2d9bc21daf51f3e5c81cbae2e779a6f997715d9d0d95285c509ecbd xsa91-unstable.patch $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQEcBAEBAgAGBQJTYMejAAoJEIP+FMlX6CvZ3oMH/j+7Ln89gf0rvyvwUAwK7EUj AD2fR/OSXQJVs4g0fZDSft4wgsIpbnbvcCl06tK98XAZH8Cyr0burQV4rXgQbM9e rWYRpfy4mWt7RNvwdgeBYecuEYvFIULmMC1hI+eJRtJTrB8UnpCvXLPbFktp2zXP Z+pPjck/dAjS8HKJZckL5ciy9ctTr1R50NmpqvW9FfeZAVhahmbmMiz3A5izQEQ0 BppXWdRad2J5vcR2u8k3uxweUfWM1Yg/eQAmMVvWPS45ceH+UHgqaGngBzWlM9oV SwqCDl0/8DjcQziFnKx5cdYcXfFbTzqV7SP5OzcV2BRoSvGZOVDowaXsqvt1jME= =LkmE -----END PGP SIGNATURE----- [ CONTENT OF TYPE application/octet-stream SKIPPED ] [ CONTENT OF TYPE application/octet-stream SKIPPED ]
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