Messages in this thread |  | | | Date | Fri, 1 Jul 2011 15:36:23 -0700 | | From | Kees Cook <> | | Subject | Re: [PATCH] x86: add missing verify_cpu to 32bit wakeup |
| |
Hi,
On Fri, Jul 01, 2011 at 02:26:27PM -0700, H. Peter Anvin wrote: > On 07/01/2011 02:19 PM, Kees Cook wrote: > > Some BIOSes will reset the Intel XD_DISABLE MSR bit when resuming from S3, > > which can interact poorly with ebba638ae723d8a8fc2f7abce5ec18b688b791d7. > > In 32bit PAE mode, this can lead to a fault when EFER is restored by > > the kernel wakeup routines, due to it setting the NX bit for a CPU > > that (thanks to the BIOS reset) now incorrectly thinks it lacks the NX > > feature. 64bit wakeup already handled this through its common call path > > that would hit verify_cpu(). 32bit has a separate path for restoring > > CPU state on S3 wakeup, and needed to call verify_cpu() to handle this > > situation. > > For S3, we should save/restore MISC_ENABLE instead... in fact, we > already save it, we just restore it too late.
Given that MISC_ENABLE may not be available for a given CPU, it seems that it's basically the same detection code as in verify_cpu() already. Since this bit is the only part that is needed that early, I think the patch is good the way it is (especially since it balances the 64bit path which already calls this logic). I don't think doing the full early MISC_ENABLE save/restore this early is worth it. Thoughts?
-Kees
-- Kees Cook Ubuntu Security Team
|  |