Request security fix in -stable (upstream 2c33645d366d)

[Kevin Christopher <kevinc@vmware.com>]

Stable maintainers -

Have a request to merge an upstream security fix into stable branches. 
The change avoids a userlevel-induceable kernel #GP in perf/x86 when a 
hypervisor emulates older perfmon. The issue was originally seen and 
accepted as an upstream patch proposed by Amazon in 2015; the security 
implication when on a VMware hypervisor was recently reported.

Upstream commit:
(commit) 2c33645d366d13b969d936b68b9f4875b1fdddea
(subject) perf/x86: Honor the architectural performance monitoring version

A second commit fixes a trivial build issue introduced by the above commit:
(commit) 6d6f2833bfbf296101f9f085e10488aef2601ba5
(subject) perf/x86: Fix undefined shift on 32-bit kernels

The 1st commit was released in 4.2 kernels and should cleanly backport 
quite far (at least 3.10). I have verified a 3.10 kernel is subject to 
the issue and a 4.4 kernel is not subject to the issue. The second 
commit was CCed to stable when committed, though would not be needed 
before 4.2. The second commit is not needed for the security fix, but I 
feel the maintainer should have the option to include a build fix 
introduced by the security fix.

VMware viewed the reported security issue as a likely Linux bug and 
requested communication with Linux maintainers to confirm; the reporter 
disagreed with that assessment and disclosed unilaterally. We 
subsequently identified the Linux upstream fix mentioned above, which 
tends to confirm it is a Linux bug. VMware also has an option to 
mitigate with a workaround, though we consider the workaround "risky" 
and prefer to only pursue that path if Linux -stable is unable to accept 
the upstream fix. VMware would view mitigation as a "low" severity issue 
which would go out in a "next available" release (commensurate with a 
Linux "next -stable release" cycle). The issue is only believed to 
impact Linux running on a VMware hypervisor.

Versions:
    Here I am not sure, based on unfamiliarity with Linux kernel 
stability lifecycles. I defer to stable maintainer's judgement based on 
the security implication. Possible candidates:
linux-4.1.y
linux-3.18.y
linux-3.16.y
linux-3.14.y
linux-3.12.y
linux-3.10.y
The 1st commit should apply cleanly to those kernel versions; if it does 
not, I am available to create a backport. The 2nd commit will not apply 
cleanly due to file movement on mainline 
(arch/x86/kernel/cpu/perf_event_intel.c to 
arch/x86/events/intel/core.c); however, it is trivial (<const>UL -> 
<const>ULL).

Background:
(external disclosure): https://cyseclabs.com/blog/vmware-linux-poc
(LKML discussion of upstream change in 2015):
     http://comments.gmane.org/gmane.linux.kernel/1968211

The reporter suggested there could be a higher-severity privilege 
escalation on the path as well; our analysis found the evidence of 
privilege escalation to be an artifact of pvops patching interacting 
poorly with debug symbols and thus be a non-issue.

As this is my first report to stable@vger.kernel.org, do please let me 
know if I am missing any information. I look forward to your ACK/NAK or 
any other feedback.

-Kevin Christopher (kevinc@vmware.com)