linux-kernel - Re: [tip: x86/urgent] x86/bugs: Use code segment selector for VERW operand

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Message-ID: <20241009134205.GJZwaILf_bDcWuht-k@fat_crate.local>
Date: Wed, 9 Oct 2024 15:42:05 +0200
From: Borislav Petkov <bp@...en8.de>
To: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
	linux-tip-commits@...r.kernel.org, Robert Gill <rtgill82@...il.com>,
	stable@...r.kernel.org, #@...-bot2.tec.linutronix.de,
	5.10+@...-bot2.tec.linutronix.de,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Brian Gerst <brgerst@...il.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, x86@...nel.org
Subject: Re: [tip: x86/urgent] x86/bugs: Use code segment selector for VERW
 operand

On Wed, Oct 09, 2024 at 11:24:19AM +0100, Andrew Cooper wrote:
> I'll bite.  Why do you think this form is is better?

Smaller, shorter ifdeffery block. An example speaks more than 1000 words:

arch/x86/include/asm/asm.h

> You've now got VERW_ARG leaking across the whole kernel, and a layer of
> obfuscatio^W indirection in CLEAR_CPU_BUFFERS.

We have that all around the kernel anyway.

> Admittedly, when I wrote this fragment as a suggestion[1], the 32bit
> comment was in the main comment because there really is no need for it
> to be separate.
> 
> But abstracting away VERW_ARG like this hampers legibility/clarity,
> rather than improving it IMO.

I guess we see it differently.

I don't care all that much to continue this - I'll just say that having the
CLEAR_CPU_BUFFERS macro text simpler and putting the argument complexity
abstracted away in macros reads better to me.

Oh well.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette