linux-kernel - Re: [PATCH v4 07/10] x86/ibt: Add paranoid FineIBT mode

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Message-ID: <202502241100.2F2F320F07@keescook>
Date: Mon, 24 Feb 2025 11:00:32 -0800
From: Kees Cook <kees@...nel.org>
To: Peter Zijlstra <peterz@...radead.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 07/10] x86/ibt: Add paranoid FineIBT mode

On Mon, Feb 24, 2025 at 01:37:10PM +0100, Peter Zijlstra wrote:
> Due to concerns about circumvention attacks against FineIBT on 'naked'
> ENDBR, add an additional caller side hash check to FineIBT. This
> should make it impossible to pivot over such a 'naked' ENDBR
> instruction at the cost of an additional load.
> 
> The specific pivot reported was against the SYSCALL entry site and
> FRED will have all those holes fixed up.
> 
>   https://lore.kernel.org/linux-hardening/Z60NwR4w%2F28Z7XUa@ubun/
> 
> This specific fineibt_paranoid_start[] sequence was concocted by
> Scott.
> 
> Reported-by: Jennifer Miller <jmill@....edu>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Great! I'm happy to see the pre-call checking. :)

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook