linux-kernel - Re: [PATCH 1/3] signal(i386): alternative signal stack wraparound occurs

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Message-Id: <20071003232509.929160f1.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 3 Oct 2007 23:25:09 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	linux-kernel@...r.kernel.org, mikpe@...uu.se, shiwh@...fujitsu.com
Subject: Re: [PATCH 1/3] signal(i386): alternative signal stack wraparound
 occurs

On Wed, 3 Oct 2007 15:46:32 +0200 (MEST)
Mikael Pettersson <mikpe@...uu.se> wrote:
> The proposed kernel signal delivery patch only handles the case
> where the /sigframe/ ends up overlapping the end of the altstack.
> If the sigframe remains within the altstack boundaries but the
> user-space signal handler adds an /ordinary stack frame/ that
> moves SP beyond the altstack limit, then the kernel patch solves
> nothing and recursive signals will cause altstack wraparound.
> 
> On the other hand, the user-space technique of making the lowest
> page(s) in the altstack inaccessible handles both cases of overflow.
> 
Hmm, okay. Then, this fix is not enough. I see.
I'll consider how to eduacate users.

Thanks,
-Kame
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