CVE-2014-7842 Linux kernel: kvm: reporting emulation failures to userspace

[Petr Matousek <pmatouse () redhat com>]

It was found that reporting emulation failures to user space can lead to
either local or L2->L1 DoS.

In the case of local DoS attacker needs access to MMIO area or be able
to generate port access. Note that on certain systems HPET is mapped
to userspace as part of vdso (vvar) and thus an unprivileged user may
generate MMIO transactions (and enter the emulator) this way.

Upstream patches:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=fc3a9157d314
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=a2b9e6c1a35a

References:
https://bugzilla.redhat.com/show_bug.cgi?id=1163762

-- 
Petr Matousek / Red Hat Product Security
PGP: 0xC44977CA 8107 AF16 A416 F9AF 18F3  D874 3E78 6F42 C449 77CA