FreeBSD Errata Notice FreeBSD-EN-18:07.pmap
21 June, 2018 by email@example.com | freebsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-EN-18:07.pmap Errata Notice The FreeBSD Project Topic: Incorrect TLB shootdown for Xen based guests Category: core Module: kernel Announced: 2018-06-21 Credits: Colin Percival Affects: FreeBSD 11.1 Corrected: 2018-05-22 14:36:46 UTC (stable/11, 11.2-BETA2) 2018-06-21 05:18:08 UTC (releng/11.1, 11.1-RELEASE-p11) For general information regarding FreeBSD Errata Notices and Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>. I. Background CPUs rely on a Translation Lookaside Buffer (TLB) to cache virtual memory paging information. When a page is unmapped from the virtual address space of a process on a multiprocessor system, an Inter-Processor Interrupt (IPI) may be sent to instruct other CPUs to invalidate ("shoot down") their TLB entries for the addresses in question. For virtualization-related performance reasons, FreeBSD has IPI code for the Xen platform which is separate from the generic x86 IPI code. II. Problem Description In the course of changes to the FreeBSD virtual memory system to address FreeBSD-SA-18:03.speculative_execution, changes were made to the IPIs used for shooting down TLB entries. Unfortunately, the IPI handlers for Xen were left non-PTI, even when PTI was enabled, which result in TLB shootdowns for the user mode portion of the address space not being consistently performed correctly. III. Impact Processes on Xen based guests may "see" pages of memory which were previously mapped but have since been unmapped, resulted in data being corrupted and/or processes crashing due to internal data structures becoming inconsistent. IV. Workaround Only Xen based guests are affected by this issue. All other platforms are not susceptible. For Xen based guests, disabling PTI will workaround the issue. Add the following line to /boot/loader.conf: vm.pmap.pti=0 Please be aware, by disabling PTI, the system will be vulnerable to FreeBSD-SA-18:03.speculative_execution. V. Solution Perform one of the following: 1) Upgrade your system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date. Afterward, reboot the system. 2) To update your system via a binary patch: Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility: # freebsd-update fetch # freebsd-update install Afterward, reboot the system. 3) To update your system via a source code patch: The following patches have been verified to apply to the applicable FreeBSD release branches. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. [FreeBSD 11.1] # fetch https://security.FreeBSD.org/patches/EN-18:07/pmap.patch # fetch https://security.FreeBSD.org/patches/EN-18:07/pmap.patch.asc # gpg --verify pmap.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in <URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/11/ r334047 releng/11.1/ r335466 - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: <URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN> VII. References The latest revision of this notice is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-18:07.pmap.asc> -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE/A6HiuWv54gCjWNV05eS9J6n5cIFAlsrN3hfFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEZD MEU4NzhBRTVBRkU3ODgwMjhENjM1NUQzOTc5MkY0OUVBN0U1QzIACgkQ05eS9J6n 5cIOow/+P+zdQ8dmZcEIy7HjYdpTAbPIGNnSdvuXV5O5XGamOziTJOuEEDBxeNiE QE9VM8a94Ybl0CJZhfBVPhqrDpYuXOqKvnfHlcXWjppDliUPWohF6kTj4ugqGKrl T2VckEvjltgJQ1/XqnkE7n1LuezLcqF/RbW3xOeRkAhf3X+IXd/E3uCuw/n4yknl O5EvLmjq3bGlN7OfHOM4E+PHvYOxxfbjYH5S+1Z9g0/apR6HOUi9WU0hV5YEB9Cz hUCsnx15Nla97jD9P1xy0tr3FkPpvZRJGj2BelNaQoFNrZB7oWB9xwOmwSqxye/b zvp+/WUuGlo1KWU8RldzVPP6A7piuL6oAvYqW8/wcpwd9HqNGXblWz1XodpE3x1F TKHTGcP/e/wgU6810SolylwJKxhGVZaQK3UH1iVKPRRTw+HUR1OVDY+q7XAyFD7c QbKRyWQIYr2X98LhiT8TMVssharFg7AcviRSDEdCYt+A6S9jiDWMe+C3hGndSSET Cf/0q6PQ89GQKw3lQOgwvtWlMaKPwfg3W8lxkusK5o935aXWhbRee3Hzkld7eUl0 8/uGBCgDnSk7hPIHLDcddIKI+QT0IpHKCPlBRRoTJUhpXo/g5bVkbUnMKBZ7zf3O mBvci+KPc2yqp///fw1eMhgRTOOOOnXAHUMsb/FH1b+yIcikudo= =fw9I -----END PGP SIGNATURE----- _______________________________________________ firstname.lastname@example.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-announce To unsubscribe, send any mail to "email@example.com"