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

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Message-ID: <086BE61B-DCCC-4105-90A2-295A487C7F6F@zytor.com>
Date:	Wed, 02 Mar 2016 09:53:28 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>
CC:	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 March 2, 2016 8:25:30 AM PST, Borislav Petkov <bp@...en8.de> wrote:
>On Wed, Mar 02, 2016 at 11:22:30AM -0500, Brian Gerst wrote:
>> This should be: movq stack_start(%rip), %rsp
>
>No it wouldn't. That doesn't work.
>
>> > +       subq    $__START_KERNEL_map, %rsp
>> 
>> It would be better to add the offset to the initializer for
>> stack_start instead of adjusting it at runtime.  That would require
>> moving the existing load of stack_start from the common path to the
>> secondary startup,
>
>This is the BSP we're talking about - no secondary startup. We want to
>run
>verify_cpu as early as possible.

Please explain why we can't use rip-relative addressing in some form...
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