linux-kernel - Re: [PATCH 4/5] x86/alternatives: Add an auxilary section

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Date:	Thu, 21 Jan 2016 11:00:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] x86/alternatives: Add an auxilary section

On 01/21/16 10:34, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Add .altinstr_aux for additional instructions which will be used before
> and/or during patching. All stuff which needs more sophisticated
> patching should go there. See next patch.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/kernel/vmlinux.lds.S | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 74e4bf11f562..1335ff4854ae 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -244,6 +244,15 @@ SECTIONS
>  	 */
>  	.altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) {
>  		*(.altinstr_replacement)
> +		/*
> +		 * Section for code used exclusively before alternatives are
> +		 * run. All references to such code must be patched out by
> +		 * alternatives, normally by using a patch with
> +		 * X86_FEATURE_ALWAYS.
> +		 *
> +		 * See static_cpu_has() for an example.
> +		 */
> +		*(.altinstr_aux)
>  	}

NAK on this being part of .altinstr_replacement (if anything it ought to
simply be part of .text.init).  Otherwise fine.

	-hpa