linux-kernel - Re: [PATCH v3 16/16] objtool: Validate kCFI calls

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Message-ID: <llyr3xzwbywv45ckdpzdco6g5ek3yu2lqqkxupgxaflrhsm42w@7of74nnyjhqt>
Date: Wed, 16 Jul 2025 14:03:58 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, kys@...rosoft.com, haiyangz@...rosoft.com, 
	wei.liu@...nel.org, decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, seanjc@...gle.com, 
	pbonzini@...hat.com, ardb@...nel.org, kees@...nel.org, Arnd Bergmann <arnd@...db.de>, 
	gregkh@...uxfoundation.org, linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kvm@...r.kernel.org, linux-efi@...r.kernel.org, samitolvanen@...gle.com, 
	ojeda@...nel.org
Subject: Re: [PATCH v3 16/16] objtool: Validate kCFI calls

On Mon, Jul 14, 2025 at 12:20:27PM +0200, Peter Zijlstra wrote:
> Validate that all indirect calls adhere to kCFI rules. Notably doing
> nocfi indirect call to a cfi function is broken.
> 
> Apparently some Rust 'core' code violates this and explodes when ran
> with FineIBT.
> 
> All the ANNOTATE_NOCFI_SYM sites are prime targets for attackers.
> 
>  - runtime EFI is especially henous because it also needs to disable
>    IBT. Basically calling unknown code without CFI protection at
>    runtime is a massice security issue.
> 
>  - Kexec image handover; if you can exploit this, you get to keep it :-)
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>

-- 
Josh