linux-kernel - Re: [PATCH] use canary at end of stack to indicate overruns at oops time

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Date:	Tue, 22 Apr 2008 11:44:12 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Eric Sandeen <sandeen@...hat.com>,
	linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] use canary at end of stack to indicate overruns at	oops
 time

Ingo Molnar wrote:
> * Eric Sandeen <sandeen@...hat.com> wrote:

>> With the code in place, an intentionally-bloated stack oops does:
>>
>> BUG: unable to handle kernel paging request at ffff8103f84cc680
>> IP: [<ffffffff810253df>] update_curr+0x9a/0xa8
>> PGD 8063 PUD 0 
>> Thread overran stack or stack corrupted
>> Oops: 0000 [1] SMP 
>> CPU 0 
>> ...
> 
> excellent. I've queued this up, it's definitely an improvement in 
> debuggability.

Crud, just realized this probably doesn't play well with
CONFIG_DEBUG_STACK_USAGE.  I think it will need something like:

Index: linux-2.6.25-rc7/kernel/exit.c
===================================================================
--- linux-2.6.25-rc7.orig/kernel/exit.c	2008-04-20 22:34:16.000000000 -0500
+++ linux-2.6.25-rc7/kernel/exit.c	2008-04-22 11:38:05.769412824 -0500
@@ -826,6 +826,8 @@ static void check_stack_usage(void)
 	unsigned long *n = end_of_stack(current);
 	unsigned long free;

+	n++;	/* skip over canary at end */
+
 	while (*n == 0)
 		n++;
 	free = (unsigned long)n - (unsigned long)end_of_stack(current);


Testing now... want me to resend the whole patch, Ingo, or you want to
just fix it up?  (I'll follow up with the testing results)

Thanks,
-Eric
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