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

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Message-ID: <20241009061102.GBZwYediMceBEfSEFo@fat_crate.local>
Date: Wed, 9 Oct 2024 08:11:02 +0200
From: Borislav Petkov <bp@...en8.de>
To: linux-kernel@...r.kernel.org
Cc: linux-tip-commits@...r.kernel.org, Robert Gill <rtgill82@...il.com>,
	Andrew Cooper <andrew.cooper3@...rix.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 Tue, Oct 08, 2024 at 10:45:36PM -0000, tip-bot2 for Pawan Gupta wrote:
>  .macro CLEAR_CPU_BUFFERS
> -	ALTERNATIVE "", __stringify(verw _ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF
> +#ifdef CONFIG_X86_64
> +	ALTERNATIVE "", "verw mds_verw_sel(%rip)", X86_FEATURE_CLEAR_CPU_BUF
> +#else
> +	/*
> +	 * In 32bit mode, the memory operand must be a %cs reference. The data
> +	 * segments may not be usable (vm86 mode), and the stack segment may not
> +	 * be flat (ESPFIX32).
> +	 */
> +	ALTERNATIVE "", "verw %cs:mds_verw_sel", X86_FEATURE_CLEAR_CPU_BUF
> +#endif

So why didn't we ifdef the "verw mds_verw_sel(%rip)" and "verw
%cs:mds_verw_sel" macro argument instead of adding more bigger ugly ifdeffery?

-- 
Regards/Gruss,
    Boris.

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