linux-kernel - Re: [PATCH 3/5] signal(x86_ia32): add a signal stack overflow check

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Message-ID: <47BA3D96.8070208@cn.fujitsu.com>
Date:	Tue, 19 Feb 2008 10:23:18 +0800
From:	Shi Weihua <shiwh@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 3/5] signal(x86_ia32): add a signal stack overflow check

The similar check has been added to x86_32(i386) in commit
id 83bd01024b1fdfc41d9b758e5669e80fca72df66.
So we add this check to x86_ia32 and improve it a liitle bit in that
we need to check for stack overflow only when the signal is on stack.

Signed-off-by: Shi Weihua <shiwh@...fujitsu.com> 

---

The previous patch has a comment mistake. Now I correct it.

---
--- linux-2.6.25-rc2.orig/arch/x86/ia32/ia32_signal.c	2008-02-16 04:57:20.000000000 +0800
+++ linux-2.6.25-rc2/arch/x86/ia32/ia32_signal.c	2008-02-19 09:56:43.000000000 +0800
@@ -406,8 +406,19 @@ static void __user *get_sigframe(struct 
 
 	/* This is the X/Open sanctioned signal stack switching.  */
 	if (ka->sa.sa_flags & SA_ONSTACK) {
-		if (sas_ss_flags(sp) == 0)
+		int onstack = sas_ss_flags(sp);
+
+		if (onstack == 0)
 			sp = current->sas_ss_sp + current->sas_ss_size;
+		else if (onstack == SS_ONSTACK) {
+			/*
+			 * If we are on the alternate signal stack and would
+			 * overflow it, don't. Return an always-bogus address
+			 * instead so we will die with SIGSEGV.
+			 */
+			 if (!likely(on_sig_stack(sp - frame_size)))
+				return (void __user *) -1L;
+		}
 	}
 
 	/* This is the legacy signal stack switching. */


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