linux-hardening - Re: [PATCH v4 0/5] Next revision of the L1D flush patches

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Date:   Thu, 13 May 2021 11:06:14 +1000
From:   Balbir Singh <bsingharora@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kees Cook <keescook@...omium.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 0/5] Next revision of the L1D flush patches

On Tue, Apr 27, 2021 at 12:24:16AM +0200, Thomas Gleixner wrote:
> On Mon, Apr 26 2021 at 10:31, Thomas Gleixner wrote:
> > On Thu, Apr 08 2021 at 13:23, Kees Cook wrote:
> >>
> >> I'd still really like to see this -- it's a big hammer, but that's the
> >> point for cases where some new flaw appears and we can point to the
> >> toolbox and say "you can mitigate it with this while you wait for new
> >> kernel/CPU."
> >>
> >> Any further thoughts from x86 maintainers? This seems like it addressed
> >> all of tglx's review comments.
> >
> > Sorry for dropping the ball on this. It's in my list of things to deal
> > with. Starting to look at it now.
> 
> So I went through the pile and for remorse I sat down and made the
> tweaks I think are necessary myself.
> 
> I've pushed out the result to
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git x86/l1dflush
>

Thank you I'll take a look and test it.
 
> The only thing I did not address yet is that the documentation lacks any
> mentioning of the SIGBUS mechanism which is invoked when a task which
> asked for L1D flush protection ends up on a SMT sibling for whatever
> reason. That's essential to have because it's part of the contract of
> that prctl.

IIRC I documented it, I'll double check.

> 
> Balbir, can you please double check the result and prepare an updated
> version from there?
> 
> If you don't have cycles, please let me know.
>

I might have some cycles for testing and re-review. Thanks for all the
hard work on this

Balbir Singh.