linux-kernel - Re: [RFC][PATCH 04/17] objtool/x86: Fix SRSO mess

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Message-ID: <20230810152239.GC212435@hirez.programming.kicks-ass.net>
Date:   Thu, 10 Aug 2023 17:22:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, jpoimboe@...nel.org,
        gregkh@...uxfoundation.org
Subject: Re: [RFC][PATCH 04/17] objtool/x86: Fix SRSO mess

On Thu, Aug 10, 2023 at 05:02:01PM +0200, Borislav Petkov wrote:
> On Thu, Aug 10, 2023 at 02:50:05PM +0200, Peter Zijlstra wrote:
> > Notably 'call RET' is not what this is about. I hope the below
> > clarifies.
> 
> Yah, it does, now that you've taken the time to explain it. Looking at
> the commit which added it:
> 
>   15e67227c49a ("x86: Undo return-thunk damage")
> 
> it doesn't even begin to explain it. Can you please put the gist of what
> you've explained here in a comment over patch_return() as it is not
> really obvious - at least to me it isn't - what the rules for the thunks
> are.
> 
> I mean, they're clear now but I think we should hold them down
> explicitly. Especially with all the crazy patching we're doing now.

Will update.