linux-kernel - Re: [PATCH v2 00/11] Fix up SRSO stuff

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Date:   Mon, 14 Aug 2023 21:57:33 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, gregkh@...uxfoundation.org,
        nik.borisov@...e.com
Subject: Re: [PATCH v2 00/11] Fix up SRSO stuff

On Mon, Aug 14, 2023 at 12:51:53PM -0700, Josh Poimboeuf wrote:
> >  * 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?

Well, I guess that comment is still not good enough. Not the RET must be
cacheline-aligned but the function return sequences must be.

IOW, we need this:

<--- cacheline begin
SYM_INNER_LABEL(retbleed_return_thunk, SYM_L_GLOBAL)
        ret
        int3


and

<--- cacheline begin
SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL)
        lea 8(%_ASM_SP), %_ASM_SP
        ret
        int3

I'll improve on it before I apply it.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette