|Public release ||2014-09-23 12:00|
|Updated ||2014-09-24 10:29|
|Title ||Missing privilege level checks in x86 emulation of software interrupts|
Filesadvisory-106.txt (signed advisory file)
-----BEGIN PGP SIGNED MESSAGE-----
Xen Security Advisory CVE-2014-7156 / XSA-106
Missing privilege level checks in x86 emulation of software interrupts
UPDATES IN VERSION 3
This issue has been assigned CVE-2014-7156.
The emulation of instructions which generate software interrupts fails
to perform supervisor mode permission checks.
However these instructions are not usually handled by the emulator.
Exceptions to this are
- - when a memory operand (implicit for the affected instructions) lives
in (emulated or passed through) memory mapped IO space,
- - in the case of guests running in 32-bit PAE mode, when such an
instruction is (in execution flow) within four instructions of one
doing a page table update,
- - when an Invalid Opcode exception gets raised by a guest instruction,
and the guest then (likely maliciously) alters the instruction to
become one of the affected ones,
- - when the guest is in real mode (in which case there are no privilege
Malicious HVM guest user mode code may be able to crash the guest.
Xen versions from 3.3 onwards are vulnerable.
Only user processes in HVM guests can take advantage of this
Running only PV guests will avoid this issue.
There is no mitigation available for HVM guests.
This issue was discovered Andrei Lutas at BitDefender and analyzed by
Andrew Cooper at Citrix.
Applying the attached patch resolves this issue.
xsa106.patch xen-unstable, Xen 4.4.x, Xen 4.3.x, Xen 4.2.x
$ sha256sum xsa106*.patch
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
-----END PGP SIGNATURE-----
Xenproject.org Security Team