FreeBSD Security Advisory FreeBSD-SA-18:03.speculative_execution
14 March, 2018 by email@example.com | freebsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-18:03.speculative_execution Security Advisory The FreeBSD Project Topic: Speculative Execution Vulnerabilities Category: core Module: kernel Announced: 2018-03-14 Credits: Jann Horn (Google Project Zero); Werner Haas, Thomas Prescher (Cyberus Technology); Daniel Gruss, Moritz Lipp, Stefan Mangard, Michael Schwarz (Graz University of Technology); Paul Kocher; Daniel Genkin (University of Pennsylvania and University of Maryland), Mike Hamburg (Rambus); Yuval Yarom (University of Adelaide and Data6) Affects: All supported versions of FreeBSD. Corrected: 2018-02-17 18:00:01 UTC (stable/11, 11.1-STABLE) 2018-03-14 04:00:00 UTC (releng/11.1, 11.1-RELEASE-p8) CVE Name: CVE-2017-5715, CVE-2017-5754 Special Note: Speculative execution vulnerability mitigation is a work in progress. This advisory addresses the most significant issues for FreeBSD 11.1 on amd64 CPUs. We expect to update this advisory to include 10.x for amd64 CPUs. Future FreeBSD releases will address this issue on i386 and other CPUs. freebsd-update will include changes on i386 as part of this update due to common code changes shared between amd64 and i386, however it contains no functional changes for i386 (in particular, it does not mitigate the issue on i386). For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>. I. Background Many modern processors have implementation issues that allow unprivileged attackers to bypass user-kernel or inter-process memory access restrictions by exploiting speculative execution and shared resources (for example, caches). II. Problem Description A number of issues relating to speculative execution were found last year and publicly announced January 3rd. Two of these, known as Meltdown and Spectre V2, are addressed here. CVE-2017-5754 (Meltdown) - ------------------------ This issue relies on an affected CPU speculatively executing instructions beyond a faulting instruction. When this happens, changes to architectural state are not committed, but observable changes may be left in micro- architectural state (for example, cache). This may be used to infer privileged data. CVE-2017-5715 (Spectre V2) - -------------------------- Spectre V2 uses branch target injection to speculatively execute kernel code at an address under the control of an attacker. III. Impact An attacker may be able to read secret data from the kernel or from a process when executing untrusted code (for example, in a web browser). IV. Workaround No workaround is available. V. Solution Perform one of the following: 1) Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date, and reboot. 2) To update your vulnerable 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, followed by a reboot into the new kernel: # freebsd-update fetch # freebsd-update install # shutdown -r now 3) To update your vulnerable 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/SA-18:03/speculative_execution-amd64-11.patch # fetch https://security.FreeBSD.org/patches/SA-18:03/speculative_execution-amd64-11.patch.asc # gpg --verify speculative_execution-amd64-11.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 CVE-2017-5754 (Meltdown) - ------------------------ The mitigation is known as Page Table Isolation (PTI). PTI largely separates kernel and user mode page tables, so that even during speculative execution most of the kernel's data is unmapped and not accessible. A demonstration of the Meltdown vulnerability is available at https://github.com/dag-erling/meltdown. A positive result is definitive (that is, the vulnerability exists with certainty). A negative result indicates either that the CPU is not affected, or that the test is not capable of demonstrating the issue on the CPU (and may need to be modified). A patched kernel will automatically enable PTI on Intel CPUs. The status can be checked via the vm.pmap.pti sysctl: # sysctl vm.pmap.pti vm.pmap.pti: 1 The default setting can be overridden by setting the loader tunable vm.pmap.pti to 1 or 0 in /boot/loader.conf. This setting takes effect only at boot. PTI introduces a performance regression. The observed performance loss is significant in microbenchmarks of system call overhead, but is much smaller for many real workloads. CVE-2017-5715 (Spectre V2) - -------------------------- There are two common mitigations for Spectre V2. This patch includes a mitigation using Indirect Branch Restricted Speculation, a feature available via a microcode update from processor manufacturers. The alternate mitigation, Retpoline, is a feature available in newer compilers. The feasibility of applying Retpoline to stable branches and/or releases is under investigation. The patch includes the IBRS mitigation for Spectre V2. To use the mitigation the system must have an updated microcode; with older microcode a patched kernel will function without the mitigation. IBRS can be disabled via the hw.ibrs_disable sysctl (and tunable), and the status can be checked via the hw.ibrs_active sysctl. IBRS may be enabled or disabled at runtime. Additional detail on microcode updates will follow. The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/11/ r329462 releng/11.1/ r330908 - ------------------------------------------------------------------------- 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 <URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-5715> <URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-5754> The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:03.speculative_execution.asc> -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE/A6HiuWv54gCjWNV05eS9J6n5cIFAlqon0RfFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEZD MEU4NzhBRTVBRkU3ODgwMjhENjM1NUQzOTc5MkY0OUVBN0U1QzIACgkQ05eS9J6n 5cKORw/+Lc5lxLhDgU1rQ0JF6sb2b80Ly5k+rJLXFWBvmEQt0uVyVkF4TMJ99M04 bcmrLbT4Pl0Csh/iEYvZQ4el12KvPDApHszsLTBgChD+KfCLvCZvBZzasgDWGD0E JhL4eIX0wjJ4oGGsT+TAqkmwXyAMJgWW/ZgZPFVXocylZTL3fV4g52VdG1Jnd2yu hnkViH2kVlVJqXX9AHlenIUfEmUiRUGrMh5oPPpFYDDmfJ+enZ8QLxfZtOKIliD7 u+2GP8V/bvaErkxqF5wwobybrBOMXpq9Y/fWw0EH/om7myevj/oORqK+ZmGZ17bl IRbdWxgjc1hN2TIMVn9q9xX6i0I0wSPwbpLYagKnSnE8WNVUTZUteaj1GKGTG1rj DFH2zOLlbRr/IXUFldM9b6VbZX6G5Ijxwy1DJzB/0KL5ZTbAReUR0pqHR7xpulbJ eDv8SKCwYiUpMuwPOXNdVlVLZSsH5/9A0cyjH3+E+eIhM8qyxw7iRFwA0DxnGVkr tkMo51Vl3Gl7JFFimGKljsE9mBh00m8B0WYJwknvfhdehO4WripcwI7/V5zL6cwj s018kaW4Xm77LOz6P1iN8nbcjZ9gN2AsPYUYYZqJxjCcZ7r489Hg9BhbDf0QtC0R gnwZWiZ/KuAy0C6vaHljsm0xPEM5nBz/yScFXDbuhEdmEgBBD6w= =fqrI -----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"