linux-kernel - Re: [PATCH] consider stack access while checking for alternate signal stack

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Message-Id: <20091020211116.2B76F81A3@magilla.sf.frob.com>
Date:	Tue, 20 Oct 2009 14:11:16 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Haavard Skinnemoen <hskinnemoen@...el.com>
Subject: Re: [PATCH] consider stack access while checking for alternate
 signal stack

> >+#ifdef CONFIG_STACK_GROWSUP
> >+	return sp >= current->sas_ss_sp &&
> >+		sp - current->sas_ss_sp < current->sas_ss_size;
> 
> CONFIG_STACK_GROWSUP is wrong: If your stack grows up and sp ==
> sas_ss_sp + size than you are using the last entry in your sig stack
> which will be not recognized correctly. 

+		sp - current->sas_ss_sp <= current->sas_ss_size;

then?

> The case where sp == sas_ss_sp
> is also not detected correctly but this should not happen in real life.

So you say that sp==sas_ss_sp should not be considered "on the sig stack"?

> That is the PRE case which is the only relevant since we don't have any
> POST architectures. The check here produces the same results as my
> variant so it is okay :)
> So you prefer the smaller patch with comments around it?

Yes, I think it is far clearer and easier to read than what you posted.


Thanks,
Roland
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