Date: Tue, 21 Jul 2020 11:01:54 +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-team-members@....org> Subject: Xen Security Advisory 329 v3 (CVE-2020-15852) - Linux ioperm bitmap context switching issues -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2020-15852 / XSA-329 version 3 Linux ioperm bitmap context switching issues UPDATES IN VERSION 3 ==================== CVE assigned. ISSUE DESCRIPTION ================= Linux 5.5 overhauled the internal state handling for the iopl() and ioperm() system calls. Unfortunately, one aspect on context switch wasn't wired up correctly for the Xen PVOps case. IMPACT ====== IO port permissions don't get rescinded when context switching to an unprivileged task. Therefore, all userspace can use the IO ports granted to the most recently scheduled task with IO port permissions. VULNERABLE SYSTEMS ================== Only x86 guests are vulnerable. All versions of Linux from 5.5 are potentially vulnerable. Linux is only vulnerable when running as x86 PV guest. Linux is not vulnerable when running as an x86 HVM/PVH guests. The vulnerability can only be exploited in domains which have been granted access to IO ports by Xen. This is typically only the hardware domain, and guests configured with PCI Passthrough. MITIGATION ========== Running only HVM/PVH guests avoids the vulnerability. CREDITS ======= This issue was discovered by Andy Lutomirski. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa329.patch Linux 5.5 and later $ sha256sum xsa329* cdb5ac9bfd21192b5965e8ec0a1c4fcf12d0a94a962a8158cd27810e6aa362f0 xsa329.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deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable.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/4UyVfoK9kFAl8WytoMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZ4wsH/0/2AMv2kb/Q6rfwlNLSrnDbK2b6bb/QUE+0GcHO vrJ7Su53xrt7mllk/P4jYmtXfyUeJzfsahdb5GQVh4GBxOA3YGgS5T4pdpnwNoFi NFZV35qOT0muwpjE/zoefKsESuvqWjd28Vssm4HrllJ4YqcGik9clo6Y5qWMFcFH rlgchZinl5RtqAzMnuOdirWir7Xika6KdkXWi56CjKZBB5ozoqfH5JKi/XbWbwrz ZoFHXwKRuckuQSxUlvdpmI7MZDyggii3OhdvA6fIMDWq58EjSVVatrvDxYsGRL8x 4PXmFPBp+871GjLQuQZ294fZH3DaZLWSrzvmwC8uZJr5uds= =Wdnv -----END PGP SIGNATURE----- Download attachment "xsa329.patch" of type "application/octet-stream" (5266 bytes)
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