lkml.org 
[lkml]   [2018]   [Jan]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB
From
Date
On Sun, 2018-01-21 at 20:54 +0100, Borislav Petkov wrote:
> On Sun, Jan 21, 2018 at 07:31:39PM +0000, David Woodhouse wrote:
> > >         if (boot_cpu_has(X86_FEATURE_IBPB))
> > >                 wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);
> > > 
> > > Problem solved.
> > 
> > Nope. Plenty of patch sets *did* have the bug above though, until it
> > was spotted.
>
> And that bug is...?

That bug is the *reason* we're arguing about static_cpu_has vs.
ALTERNATIVE. 

A conditional branch that the CPU sees can be speculated over...

Now, Andrew is right that in a number of cases there will be another
serialising instruction before we ever hit a problematic indirect
branch. But as I just said elsewhere, I'd really like the *primitives*
to support unconditional operation.[unhandled content-type:application/x-pkcs7-signature]
\
 
 \ /
  Last update: 2018-01-21 21:07    [W:0.049 / U:0.480 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site