Messages in this thread | | | Date | Wed, 09 Apr 2014 11:38:02 -0400 | From | Boris Ostrovsky <> | Subject | Re: [Xen-devel] [PATCH] x86/xen: Fix 32-bit PV guests's usage of kernel_stack |
| |
On 04/09/2014 11:01 AM, Jan Beulich wrote: >>>> On 09.04.14 at 16:41, <andrew.cooper3@citrix.com> wrote: >> The latter load however can easy fault; The arguments for %ds in >> XSA-42/ CVE-2013-0228 applies to %{e,f,g}s as well. > And it was only that latter operation that I pointed at.
We don't seem to reference %fs after the pop so doing the fixup (as David suggested) should be enough?
-boris
> >> Furthermore, I am a little concerned about the performance impact of >> this. I would have thought that in most cases, %fs will already be >> correct, at which point reloading it twice is a waste of time. > Why would you expect %fs on the IRET path to commonly point to the > kernel segment rather than whatever user mode wants/needs? Also, I'm > not sure adding conditionals here wouldn't harm performance about as > much as the save/load/restore. If anything I'd look into open coding > GET_THREAD_INFO() without using %fs for this single case. > > Jan > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel
| |