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Category:   OS (UNIX)  >   NetBSD Vendors:   NetBSD
(NetBSD Issues Fix) FreeBSD Floating Point Unit Kernel Implementation Error May Let Local Users Obtain Sensitive Information
SecurityTracker Alert ID:  1016251
SecurityTracker URL:
CVE Reference:   CVE-2006-1056   (Links to External Site)
Date:  Jun 8 2006
Impact:   Disclosure of authentication information, Disclosure of system information, Disclosure of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 2.0, 2.1, 3.0
Description:   A vulnerability was reported in FreeBSD when running on AMD processors. A local user may be able to obtain sensitive information. NetBSD is also affected.

On "7th generation" and "8th generation" processors manufactured by AMD, the fxsave and fxrstor instructions do not save and restore the FOP, FIP, and FDP registers unless the exception summary bit (ES) in the x87 status word is set (whereas other processors store this information regardless of the ES bit).

As a result, the FreeBSD kernel does not restore the contents of the FOP, FIP, and FDP registers between context switches. This may allow a local user to monitor the execution path of a process that uses floating-point operations to obtain potentially sensitive information.

Systems that do not use AMD Athlon, Duron, Athlon MP, Athlon XP, Athlon64, Athlon64 FX, Opteron, Turion, or Sempron processors are not affected.

The vendor credits Jan Beulich with reporting this vulnerability.

Impact:   A local user can monitor the execution path of a process that uses floating-point operations, which may allow the user to obtain cryptographic keys or other potentially sensitive information.
Solution:   NetBSD has released a kernel fix. NetBSD is affected by this vulnerability.

The NetBSD advisory is available at:

Cause:   Access control error

Message History:   This archive entry is a follow-up to the message listed below.
Apr 19 2006 FreeBSD Floating Point Unit Kernel Implementation Error May Let Local Users Obtain Sensitive Information

 Source Message Contents

Subject:  NetBSD Security Advisory 2006-015: FPU Information leak on

Hash: SHA1

		 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


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 

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 

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
	# ./ 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:

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

Information about NetBSD and NetBSD security can be found at and

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 $

Version: GnuPG v1.4.3 (NetBSD)



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