linux-kernel - Re: [PATCH v4 08/10] x86: BHI stubs

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Message-ID: <20250225085212.GG11590@noisy.programming.kicks-ass.net>
Date: Tue, 25 Feb 2025 09:52:12 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kees Cook <kees@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, alyssa.milburn@...el.com,
	scott.d.constable@...el.com, joao@...rdrivepizza.com,
	andrew.cooper3@...rix.com, jpoimboe@...nel.org,
	jose.marchesi@...cle.com, hjl.tools@...il.com,
	ndesaulniers@...gle.com, samitolvanen@...gle.com, nathan@...nel.org,
	ojeda@...nel.org, alexei.starovoitov@...il.com, mhiramat@...nel.org,
	jmill@....edu
Subject: Re: [PATCH v4 08/10] x86: BHI stubs

On Mon, Feb 24, 2025 at 11:01:02AM -0800, Kees Cook wrote:

> On Mon, Feb 24, 2025 at 01:37:11PM +0100, Peter Zijlstra wrote:
> > 
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> 
> Did this commit log go missing?

Nah, it never had one.

How does this sound?

---

Add an array of code thunks, to be called from the FineIBT preamble,
clobbering the first 'n' argument registers for speculative execution.

Notably the 0th entry will clobber no argument registers and will never
be used, it exists so the array can be naturally indexed, while the 7th
entry will clobber all the 6 argument registers and also RSP in order to
mess up stack based arguments.