linux-kernel - Re: [RFC PATCH] x86: Make sure verify

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Message-ID: <20160302181556.GD8362@pd.tnic>
Date:	Wed, 2 Mar 2016 19:15:56 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Brian Gerst <brgerst@...il.com>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFC PATCH] x86: Make sure verify_cpu has a good stack

On Wed, Mar 02, 2016 at 09:53:28AM -0800, H. Peter Anvin wrote:
> Please explain why we can't use rip-relative addressing in some form...

We *can* do almost what Brian suggested:

        movq    stack_start(%rip), %rsp
        subq    $__START_KERNEL_map, %rsp

But we still have to subtract __START_KERNEL_map.

-- 
Regards/Gruss,
    Boris.

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