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

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Message-Id: <20091019180810.3CB751E@magilla.sf.frob.com>
Date:	Mon, 19 Oct 2009 11:08:10 -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

AFAICT all you want is the following, and I'm not sure it requires all that
much explanation.  I've probably missed some subtlety.


Thanks,
Roland

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2090,7 +2090,13 @@ static inline int is_si_special(const struct siginfo *info)
 
 static inline int on_sig_stack(unsigned long sp)
 {
-	return (sp - current->sas_ss_sp < current->sas_ss_size);
+#ifdef CONFIG_STACK_GROWSUP
+	return sp >= current->sas_ss_sp &&
+		sp - current->sas_ss_sp < current->sas_ss_size;
+#else
+	return sp > current->sas_ss_sp &&
+		sp - current->sas_ss_sp <= current->sas_ss_size;
+#endif
 }
 
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