lkml.org 
[lkml]   [2023]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 00/11] Fix up SRSO stuff
On Mon, Aug 14, 2023 at 12:51:55PM -0700, Josh Poimboeuf wrote:
> On Mon, Aug 14, 2023 at 06:44:47PM +0200, Borislav Petkov wrote:
> > On Mon, Aug 14, 2023 at 01:44:26PM +0200, Peter Zijlstra wrote:
> > > The one open techinical issue I have with the mitigation is the alignment of
> > > the RET inside srso_safe_ret(). The details given for retbleed stated that RET
> > > should be on a 64byte boundary, which is not the case here.
> >
> > I have written this in the hope to make this more clear:
> >
> > /*
> > * Some generic notes on the untraining sequences:
> > *
> > * They are interchangeable when it comes to flushing potentially wrong
> > * RET predictions from the BTB.
> > *
> > * The SRSO Zen1/2 (MOVABS) untraining sequence is longer than the
> > * Retbleed sequence because the return sequence done there
> > * (srso_safe_ret()) is longer and the return sequence must fully nest
> > * (end before) the untraining sequence. Therefore, the untraining
> > * sequence must overlap the return sequence.
> > *
> > * Regarding alignment - the instructions which need to be untrained,
> > * must all start at a cacheline boundary for Zen1/2 generations. That
> > * is, both the ret in zen_untrain_ret() and srso_safe_ret() in the
> > * srso_untrain_ret() must both be placed at the beginning of
> > * a cacheline.
> > */
>
> It's a good comment, but RET in srso_safe_ret() is still misaligned.
> Don't we need something like so?

Scratch that, I guess I misread the confusingly worded comment:

"both the ret in zen_untrain_ret() and srso_safe_ret()..."

to mean the RET in each function.

How about:

"both the RET in zen_untrain_ret() and the LEA in srso_untrain_ret()"

?

--
Josh

\
 
 \ /
  Last update: 2023-08-14 22:02    [W:0.147 / U:0.936 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site