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Home » Security Advisories» NetBSD » FPU info leak with AMD CPUs

FPU info leak with AMD CPUs

Due to the documented behavior of AMD processors when running amd64, i386 and Xen NetBSD kernels, processors using floating point operations can leak information. This may allow a local attacker to gain sensitive privileged information.

  • Vendor: NetBSD
  • Vendor ID: 2006-015
  • Date: June 08, 2006


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NetBSD Security Advisory 2006-015
=================================

Topic: FPU Information leak on i386/amd64/Xen platforms with AMD CPUs

Version: NetBSD-current: source prior to April 19, 2006
NetBSD 3.0: affected
NetBSD 2.1: affected
NetBSD 2.0.*: affected
NetBSD 2.0: affected

Severity: Information leakage between local processes

Fixed: NetBSD-current: April 19, 2006
NetBSD-3-0 branch: May 12, 2006
(3.0.1 will include the fix)
NetBSD-3 branch: May 12, 2006
NetBSD-2-1 branch: May 12, 2006
(2.1.1 will include the fix)
NetBSD-2-0 branch: May 12, 2006
(2.0.4 will include the fix)
NetBSD-2 branch: May 12, 2006

Abstract
========

Due to the documented behavior of AMD processors when running amd64, i386
and Xen NetBSD kernels, processors using floating point operations can leak
information. This may allow a local attacker to gain sensitive privileged
information.

This vulnerability has been assigned CVE reference CVE-2006-1056.

Technical Details
=================

The FXRSTOR/FXSAVE instructions on AMD processors do not restore/save the
x87 pointer registers (FOP, FIP and FDP) unless the exception summary (ES)
bit is set to 1. This potentially allows one process to discover the
stream of floating point instructions in other local processes using FPU
exceptions.

Solutions and Workarounds
=========================

There are no known workarounds for this issue but it only applies to i386,
amd64 and Xen NetBSD kernels when using certain AMD processors.

AMD processors known to be impacted by this issue are 7th generation (e.g.
AMD Athlon, AMD Duron, AMD Athlon MP, AMD Athlon XP, and AMD Sempron) and
8th generation (e.g. AMD Athlon64, AMD Athlon64 FX, AMD Opteron, AMD Turion,
and AMD Sempron).

For all NetBSD versions, you need to obtain fixed kernel sources,
rebuild and install the new kernel, and reboot the system.

The fixed source may be obtained from the NetBSD CVS repository.

The following instructions briefly summarise how to upgrade your
kernel. In these instructions, replace:

ARCH with your architecture (from uname -m), and
KERNCONF with the name of your kernel configuration file.

To update from CVS, re-build, and re-install the kernel:

# cd src
# cvs update -d -P sys/arch/i386/isa/npx.c
# cvs update -d -P sys/arch/amd64/amd64/fpu.c
# cvs update -d -P sys/arch/xen/i386/npx.c
# ./build.sh kernel=KERNCONF
# mv /netbsd /netbsd.old
# cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd
# shutdown -r now

For more information on how to do this, see:

http://www.NetBSD.org/guide/en/chap-kernel.html


Thanks To
=========

Christos Zoulas for implementing the fixes.
Jan Beulich is credited with discovering this issue.
Richard Brunner from AMD for providing a vendor response.

Revision History
================

2006-06-08 Initial release

More Information
================

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-015.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.


Copyright 2006, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-015.txt,v 1.5 2006/06/08 16:07:09 adrianp Exp $

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