linux-kernel - Re: [PATCH] x86-64: don't leak kernel register values to 32-bit processes

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Message-ID: <20091007094248.GA1425@ucw.cz>
Date:	Wed, 7 Oct 2009 11:44:19 +0200
From:	Pavel Machek <pavel@....cz>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86-64: don't leak kernel register values to 32-bit
	processes

Hi!

> While 32-bit processes can't directly access R8...R15, they can gain
> access to these registers by temporarily switching themselves into
> 64-bit mode. Therefore, registers not preserved anyway by called C
> functions (i.e. R8...R11) must be cleared prior to returning to user
> mode.

How can userspace "temporarily switch itself" to 64bit mode?

Such ability would lead to very interesting behaviour on 32-bit
kernel, I'd say...

-- 
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