3571e53040
patches for easier mirroring, to eliminate a special copy, to make www.freebsd.org/security a full copy of security.freebsd.org and be eventually be the same. For now files are just sitting there. The symlinks are missing. Discussed on: www (repository location) Discussed with: simon (so)
140 lines
5.1 KiB
Text
140 lines
5.1 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA1
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=============================================================================
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FreeBSD-SA-08:07.amd64 Security Advisory
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The FreeBSD Project
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Topic: amd64 swapgs local privilege escalation
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Category: core
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Module: sys_amd64_amd64
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Announced: 2008-09-03
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Credits: Nate Eldredge
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Affects: All supported FreeBSD/amd64 versions.
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Corrected: 2008-08-21 09:58:18 UTC (RELENG_7, 7.0-STABLE)
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2008-09-03 19:09:47 UTC (RELENG_7_0, 7.0-RELEASE-p4)
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2008-09-03 19:09:47 UTC (RELENG_6, 6.4-PRERELEASE)
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2008-09-03 19:09:47 UTC (RELENG_6_3, 6.3-RELEASE-p4)
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CVE Name: CVE-2008-3890
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For general information regarding FreeBSD Security Advisories,
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including descriptions of the fields above, security branches, and the
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following sections, please visit <URL:http://security.FreeBSD.org/>.
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I. Background
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FreeBSD/amd64 is commonly used on 64bit systems with AMD and Intel
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CPU's. For Intel CPU's this architecture is known as EM64T or Intel
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64.
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The gs segment CPU register is used by both user processes and the
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kernel to convieniently access state data. User processes use it to
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manage per-thread data, and the kernel uses it to manage per-processor
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data. As the processor enters and leaves the kernel it uses the
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'swapgs' instruction to toggle between the kernel and user values for
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the gs register.
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The kernel stores critical information in its per-processor data
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block. This includes the currently executing process and its
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credentials.
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As the processor switches between user and kernel level, a number of
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checks are performed in order to implement the privilege protection
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system. If the processor detects a problem while attempting to switch
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privilege levels it generates a trap - typically general protection
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fault (GPF). In that case, the processor aborts the return to the
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user level process and re-enters the kernel. The FreeBSD kernel
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allows the user process to be notified of such an event by a signal
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(SIGSEGV or SIGBUS).
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II. Problem Description
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If a General Protection Fault happens on a FreeBSD/amd64 system while
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it is returning from an interrupt, trap or system call, the swapgs CPU
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instruction may be called one extra time when it should not resulting
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in userland and kernel state being mixed.
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III. Impact
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A local attacker can by causing a General Protection Fault while the
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kernel is returning from an interrupt, trap or system call while
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manipulating stack frames and, run arbitrary code with kernel
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privileges.
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The vulnerability can be used to gain kernel / supervisor privilege.
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This can for example be used by normal users to gain root privileges,
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to break out of jails, or bypass Mandatory Access Control (MAC)
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restrictions.
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IV. Workaround
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No workaround is available, but only systems running the 64 bit
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FreeSD/amd64 kernels are vulnerable.
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Systems with 64 bit capable CPUs, but running the 32 bit FreeBSD/i386
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kernel are not vulnerable.
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V. Solution
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Perform one of the following:
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1) Upgrade your vulnerable system to 6-STABLE, or 7-STABLE, or to the
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RELENG_7_0, or RELENG_6_3 security branch dated after the correction
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date.
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2) To patch your present system:
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The following patches have been verified to apply to FreeBSD 6.3 and
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7.0 systems.
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a) Download the relevant patch from the location below, and verify the
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detached PGP signature using your PGP utility.
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# fetch http://security.FreeBSD.org/patches/SA-08:07/amd64.patch
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# fetch http://security.FreeBSD.org/patches/SA-08:07/amd64.patch.asc
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b) Apply the patch.
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# cd /usr/src
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# patch < /path/to/patch
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c) Recompile your kernel as described in
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<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
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system.
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VI. Correction details
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The following list contains the revision numbers of each file that was
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corrected in FreeBSD.
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Branch Revision
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Path
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- -------------------------------------------------------------------------
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RELENG_6
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src/sys/amd64/amd64/exception.S 1.125.2.3
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RELENG_6_3
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src/UPDATING 1.416.2.37.2.9
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src/sys/conf/newvers.sh 1.69.2.15.2.8
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src/sys/amd64/amd64/exception.S 1.125.2.2.2.1
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RELENG_7
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src/sys/amd64/amd64/exception.S 1.129.2.2
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RELENG_7_0
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src/UPDATING 1.507.2.3.2.8
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src/sys/conf/newvers.sh 1.72.2.5.2.8
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src/sys/amd64/amd64/exception.S 1.129.2.1.2.1
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- -------------------------------------------------------------------------
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VII. References
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http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-3890
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The latest revision of this advisory is available at
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http://security.FreeBSD.org/advisories/FreeBSD-SA-08:07.amd64.asc
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