Update for FreeBSD Security Advisory FreeBSD-SA-12:04.sysret for 8.1

[John Baldwin]

On Tuesday, June 19, 2012 2:15:54 pm Steven Chamberlain wrote:
> Hi,
> 
> Thanks a lot of looking into this!
> 
> On 18/06/12 22:37, Simon L. B. Nielsen wrote:
> > Note that this is ONLY for FreeBSD 8.1. Other branches are OK.
> 
> Having seen the correct fix now, I'm starting to wonder if the commit to
> RELENG_7_4 was really okay too?
> 
> 
http://svnweb.freebsd.org/base/releng/7.4/sys/amd64/amd64/trap.c?annotate=236953#l975
> 
> The inserted code does not appear at the end of the function, like it
> does now in all other versions including 8.1 which is the most similar.
> 
> I expect this would at least trap if the exploit was attempted, but then
> it would omit the rest of the function, including userret();  would that
> have consequences?

It would perhaps be best to occur at the end of the function to be consistent.  
However, the fix is functionally correct in this case.

-- 
John Baldwin