linux-kernel - Re: [PATCH] Fix out-by-one error in traps.c

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Message-Id: <1188929908.10802.113.camel@localhost.localdomain>
Date:	Wed, 05 Sep 2007 04:18:17 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, lguest <lguest@...abs.org>,
	Frederik Deweerdt <deweerdt@...e.fr>, Andi Kleen <ak@....de>
Subject: Re: [PATCH] Fix out-by-one error in traps.c

On Fri, 2007-08-31 at 11:24 -0700, Linus Torvalds wrote:
> 
> On Sat, 1 Sep 2007, Rusty Russell wrote:
> > 
> > This is only for the initial booting stack (init_thread_union); see
> > arch/i386/kernel/head.S:
> > 	/* Set up the stack pointer */
> > 	lss stack_start,%esp
> > 	...
> > 	pushl $0		# fake return address for unwinder
> 
> Ok, we should fix that. We should just make it look like all other stack 
> frames.
> 
> There is other code in the kernel that "knows" that all kernel stacks have 
> the fields for the user stack return on it, namely the ptrace code etc. 
> Now, the initial stack is hopefully never *accessed* by that kind of code, 
> but this kind of special-case code is just wrong.

Yes, but -ETIMEDOUT.  Maybe for 2.6.24...

> IOW, how 
> about this one, which just declares a structure that describes the stack 
> frame thing? That just makes everything clearer, since we can then use 
> "sizeof(that structure)" instead of using the magic "2*sizeof(unsigned 
> long)".

Much nicer, thanks.

Rusty.

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