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FreeBSD-SA-12:04.sysret                                     Security Advisory
                                                          The FreeBSD Project

Topic:          Privilege escalation when returning from kernel

Category:       core
Module:         sys_amd64
Announced:      2012-06-12
Credits:        Rafal Wojtczuk, John Baldwin
Affects:        All supported versions of FreeBSD
Corrected:      2012-06-12 12:10:10 UTC (RELENG_7, 7.4-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_7_4, 7.4-RELEASE-p9)
                2012-06-12 12:10:10 UTC (RELENG_8, 8.3-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_8_3, 8.3-RELEASE-p3)
                2012-06-12 12:10:10 UTC (RELENG_8_2, 8.2-RELEASE-p9)
                2012-06-18 21:00:54 UTC (RELENG_8_1, 8.1-RELEASE-p12)
                2012-06-12 12:10:10 UTC (RELENG_9, 9.0-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_9_0, 9.0-RELEASE-p3)
CVE Name:       CVE-2012-0217

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/>.

0.   Revision History

v1.0  2012-06-12 Initial release.
v1.1  2012-06-19 Corrected patch FreeBSD 8.1.

I.   Background

The FreeBSD operating system implements a rings model of security, where
privileged operations are done in the kernel, and most applications
request access to these operations by making a system call, which puts
the CPU into the required privilege level and passes control to the
kernel.

II.  Problem Description

FreeBSD/amd64 runs on CPUs from different vendors.  Due to varying
behaviour of CPUs in 64 bit mode a sanity check of the kernel may be
insufficient when returning from a system call.

III. Impact

Successful exploitation of the problem can lead to local kernel privilege
escalation, kernel data corruption and/or crash.

To exploit this vulnerability, an attacker must be able to run code with user
privileges on the target system.

IV.  Workaround

No workaround is available.

However FreeBSD/amd64 running on AMD CPUs is not vulnerable to this
particular problem.

Systems with 64 bit capable CPUs, but running the 32 bit FreeBSD/i386
kernel are not vulnerable, nor are systems running on different
processor architectures.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE, 8-STABLE, or 9-STABLE,
or to the RELENG_7_4, RELENG_8_3, RELENG_8_2, RELENG_8_1, or RELENG_9_0
security branch dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD 7.4,
8.3, 8.2, 8.1 and 9.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[7.4, 8.3, 8.2, 9.0]
# fetch https://security.FreeBSD.org/patches/SA-12:04/sysret.patch
# fetch https://security.FreeBSD.org/patches/SA-12:04/sysret.patch.asc

[8.1]
# fetch https://security.FreeBSD.org/patches/SA-12:04/sysret-81.patch
# fetch https://security.FreeBSD.org/patches/SA-12:04/sysret-81.patch.asc

[8.1 if original sysret.patch has been applied]
# fetch https://security.FreeBSD.org/patches/SA-12:04/sysret-81-correction.patch
# fetch https://security.FreeBSD.org/patches/SA-12:04/sysret-81-correction.patch.asc

b) Apply the patch.

# 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.

3) To update your vulnerable system via a binary patch:

Systems running 7.4-RELEASE, 8.3-RELEASE, 8.2-RELEASE, 8.1-RELEASE,
or 9.0-RELEASE on the i386 or amd64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_7
  src/sys/amd64/amd64/trap.c                                   1.319.2.14
RELENG_7_4
  src/UPDATING                                            1.507.2.36.2.11
  src/sys/conf/newvers.sh                                  1.72.2.18.2.14
  src/sys/amd64/amd64/trap.c                               1.319.2.12.2.2
RELENG_8
  src/sys/amd64/amd64/trap.c                                   1.332.2.24
RELENG_8_3
  src/UPDATING                                             1.632.2.26.2.5
  src/sys/conf/newvers.sh                                   1.83.2.15.2.7
  src/sys/amd64/amd64/trap.c                               1.332.2.21.2.2
RELENG_8_2
  src/UPDATING                                            1.632.2.19.2.11
  src/sys/conf/newvers.sh                                  1.83.2.12.2.14
  src/sys/amd64/amd64/trap.c                               1.332.2.14.2.2
RELENG_8_1
  src/UPDATING                                            1.632.2.14.2.15
  src/sys/conf/newvers.sh                                  1.83.2.10.2.16
  src/sys/amd64/amd64/trap.c                               1.332.2.10.2.3
RELENG_9
  src/sys/amd64/amd64/trap.c                                    1.357.2.9
RELENG_9_0
  src/UPDATING                                              1.702.2.4.2.5
  src/sys/conf/newvers.sh                                    1.95.2.4.2.7
  src/sys/amd64/amd64/trap.c                                1.357.2.2.2.3
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/7/                                                         r236953
releng/7.4/                                                       r236953
stable/8/                                                         r236953
releng/8.3/                                                       r236953
releng/8.2/                                                       r236953
releng/8.1/                                                       r237242
stable/9/                                                         r236953
releng/9.0/                                                       r236953
- -------------------------------------------------------------------------

VII. References

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-0217

The latest revision of this advisory is available at
https://security.FreeBSD.org/advisories/FreeBSD-SA-12:04.sysret.asc
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