linux-hardening - Re: [RFC PATCH 4/7] x86: Add x86_64 Kernel Control Flow Integrity implementation

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Message-ID: <202508220135.A0ABFC1@keescook>
Date: Fri, 22 Aug 2025 01:36:43 -0700
From: Kees Cook <kees@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Qing Zhao <qing.zhao@...cle.com>, gcc-patches@....gnu.org,
	Joseph Myers <josmyers@...hat.com>,
	Richard Biener <rguenther@...e.de>, Jan Hubicka <hubicka@....cz>,
	Richard Earnshaw <richard.earnshaw@....com>,
	Richard Sandiford <richard.sandiford@....com>,
	Marcus Shawcroft <marcus.shawcroft@....com>,
	Kyrylo Tkachov <kyrylo.tkachov@....com>,
	Kito Cheng <kito.cheng@...il.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Andrew Waterman <andrew@...ive.com>,
	Jim Wilson <jim.wilson.gcc@...il.com>,
	Dan Li <ashimida.1990@...il.com>, linux-hardening@...r.kernel.org
Subject: Re: [RFC PATCH 4/7] x86: Add x86_64 Kernel Control Flow Integrity
 implementation

On Fri, Aug 22, 2025 at 10:19:15AM +0200, Peter Zijlstra wrote:
> Anyway, I might be able to deal with the indirect call not being r11,
> but it'll take a bit of prodding. Also it will shatter my plans to move
> the hash to eax to save a few bytes in instruction encoding. Let me go
> poke around with that UDB patch see what's possible.

I think I have it mostly working to force r11 when doing kcfi and
retpoline now, though I'm seeing a few glitches still. I'll keep working
on it.

-- 
Kees Cook