Bug 1585011 - (CVE-2018-3665) CVE-2018-3665 Kernel: FPU state information leakage via lazy FPU restore
CVE-2018-3665 Kernel: FPU state information leakage via lazy FPU restore
Status: NEW
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
medium Severity medium
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Assigned To: Red Hat Product Security
impact=moderate,public=20180613:2100,...
: Security
Depends On: 1589048 1589049 1589053 1590990 1589047 1589050 1589051 1589052
Blocks: 1581207 1589899 1589900 1589902 1589903
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Reported: 2018-06-01 02:52 EDT by Prasad J Pandit
Modified: 2018-08-03 16:51 EDT (History)
66 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
A Floating Point Unit (FPU) state information leakage flaw was found in the way the Linux kernel saved and restored the FPU state during task switch. Linux kernels that follow the "Lazy FPU Restore" scheme are vulnerable to the FPU state information leakage issue. An unprivileged local attacker could use this flaw to read FPU state bits by conducting targeted cache side-channel attacks, similar to the Meltdown vulnerability disclosed earlier this year.
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RHEL 7.3 requirements from Atomic Host:
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External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2018:1852 None None None 2018-06-14 16:12 EDT
Red Hat Product Errata RHSA-2018:1944 None None None 2018-06-19 09:18 EDT
Red Hat Product Errata RHSA-2018:2164 None None None 2018-07-10 13:53 EDT
Red Hat Product Errata RHSA-2018:2165 None None None 2018-07-10 13:17 EDT

  None (edit)
Description Prasad J Pandit 2018-06-01 02:52:38 EDT
An information leakage flaw is found in the way Linux kernel saves and restores Floating Point Unit(FPU) state during task switch. There are two ways, one is to save & restore FPU state during task context switch. And second is to defer FPU state save & restore until an FP instruction is invoked by the current task. First is called as "Eager FPU Restore" and second is known as "Lazy FPU Restore" scheme.

Linux kernel which follows the "Lazy FPU Restore" scheme is vulnerable to the FPU state information leakage issue. An unprivileged local attacker could use this flaw to read FPU state bits by conducting targeted cache side-channel attacks, similar to Meltdown attack disclosed earlier this year.

Upstream fix:
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  -> https://git.kernel.org/linus//58122bf1d856a4ea9581d62a07c557d997d46a19

References:
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  -> http://www.openwall.com/lists/oss-security/2018/06/13/7
Comment 4 Prasad J Pandit 2018-06-13 16:39:01 EDT
Mitigation:

RHEL-7 will automatically default to (safe) “eager” floating point register restore on Sandy Bridge and newer Intel processors. AMD processors are not affected. You can mitigate this issue on older processors by booting the kernel with the 'eagerfpu=on' parameter to enable eager FPU restore mode.  In this mode FPU state is saved and restored for every task/context switch regardless of whether the current process invokes FPU instructions or not. The parameter does not affect performance negatively, and can be applied with no adverse effects to processors that are not affected.
Comment 7 Eric Christensen 2018-06-13 19:26:37 EDT
Statement:

This issue affects the versions of the Linux kernel as shipped with Red Hat Enterprise Linux 5, 6, 7, and Red Hat Enterprise MRG 2. Future kernel updates for Red Hat Enterprise Linux 5, 6, 7, and Red Hat Enterprise MRG 2 may address this issue.
Comment 9 Petr Matousek 2018-06-14 05:09:06 EDT
Acknowledgments:

Name: Julian Stecklina (Amazon.de), Thomas Prescher (cyberus-technology.de), Zdenek Sojka (sysgo.com)
Comment 10 errata-xmlrpc 2018-06-14 16:11:53 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:1852 https://access.redhat.com/errata/RHSA-2018:1852
Comment 11 Klaas Demter 2018-06-18 03:32:07 EDT
Is there a reason for eager only being default on Sandy Bridge and newer?
Comment 12 Prasad J Pandit 2018-06-18 16:07:50 EDT
(In reply to Klaas Demter from comment #11)
> Is there a reason for eager only being default on Sandy Bridge and newer?

On Sandy Bridge and newer CPUs RHEL-7 already defaults to 'eagerfpu' mode. Latest kernel update makes 'eagerfpu' as default on earlier Intel CPUs. Please use appropriate support channel for future questions:

  -> https://access.redhat.com/ 

Thank you.
Comment 13 errata-xmlrpc 2018-06-19 09:18:23 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2018:1944 https://access.redhat.com/errata/RHSA-2018:1944
Comment 16 errata-xmlrpc 2018-07-10 13:16:52 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise MRG 2

Via RHSA-2018:2165 https://access.redhat.com/errata/RHSA-2018:2165
Comment 17 errata-xmlrpc 2018-07-10 13:53:22 EDT
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6

Via RHSA-2018:2164 https://access.redhat.com/errata/RHSA-2018:2164

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