linux-kernel - Re: [PATCH v2 05/11] x86/cpu: Clean up SRSO return thunk mess

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Date:   Mon, 14 Aug 2023 19:48:10 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, jpoimboe@...nel.org,
        gregkh@...uxfoundation.org, nik.borisov@...e.com
Subject: Re: [PATCH v2 05/11] x86/cpu: Clean up SRSO return thunk mess

On Mon, Aug 14, 2023 at 01:44:31PM +0200, Peter Zijlstra wrote:
> Where Zen1/2 flush the BTB entry using the instruction decoder trick
> (test,movabs) Zen3/4 use instruction aliasing. SRSO adds RSB (RAP in

I'll change that "instruction aliasing" to "BTB aliasing".

> AMD speak) stuffing to force speculation into a trap an cause a
> mis-predict.

I'll change that to the much more precise:

"SRSO adds a return sequence (srso_safe_ret()) which forces the function
return instruction to speculate into a trap (UD2).  This RET will then
mispredict and execution will continue at the return site read from the
top of the stack."

-- 
Regards/Gruss,
    Boris.

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