linux-kernel - Re: [PATCH 2/2] x86: ia32_signal: remove unnecessary padding

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Date:	Thu, 13 Nov 2008 09:45:12 +0100
From:	Mikael Pettersson <mikpe@...uu.se>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: ia32_signal: remove unnecessary padding

H. Peter Anvin writes:
 > Hiroshi Shimamoto wrote:
 > > H. Peter Anvin wrote:
 > >> Mikael Pettersson wrote:
 > >>> It does cause each signal delivery to leak 2 uninitialised
 > >>> kernel bytes to the end of retcode[], which seems unnecessary.
 > >> Not just unnecessary, it is a huge no-no for security.
 > > 
 > > Am I missing important thing?
 > > The frame->retcode is 8 bytes and packed structure with padding
 > > is 10 bytes each, and the code is copied to user stack 8 bytes only.
 > > 
 > > err |= __copy_to_user(frame->retcode, &code, 8);
 > > 
 > > I don't think the behavior is changed.
 > > 
 > 
 > Ah, nevermind, then.  Then it fine, obviously.

Agreed. I wonder how on earth those templates ended
up as 10 bytes large when retcode[] always has been
8 bytes.
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