linux-kernel - Re: [x86] do_arch_prctl

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Message-ID: <49247FC6.8080201@goop.org>
Date:	Wed, 19 Nov 2008 13:06:14 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Eric Lacombe <goretux@...il.com>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [x86] do_arch_prctl - bug?

Eric Lacombe wrote:
> Ok, thanks, so I suppose now that only doing :
> asm volatile("movl %0,%%gs" :: "r" (0));
> could corrupt the address of the PDA that resides actually in the MSR_GS_BASE. 
> And that's why load_gs_index is used as it contains "swapgs" before and after 
> the "mov to gs".
>
> Is that correct?
>   

Yes, loading a selector into a segment register will load the lower 32 
bits of the base from the ldt/gdt into the msr and zero the rest.

    J
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