linux-kernel - Re: [PATCH v2] use %pK for /proc/kallsyms and /proc/modules

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Date:	Fri, 4 Feb 2011 14:03:51 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-kernel@...r.kernel.org, Joe Perches <joe@...ches.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tejun Heo <tj@...nel.org>, Marcus Meissner <meissner@...e.de>,
	Jason Wessel <jason.wessel@...driver.com>,
	Eugene Teo <eugeneteo@...nel.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Len Brown <len.brown@...el.com>,
	Changli Gao <xiaosuo@...il.com>,
	Dan Rosenberg <drosenberg@...curity.com>
Subject: Re: [PATCH v2] use %pK for /proc/kallsyms and /proc/modules

On Wed, 26 Jan 2011 16:41:29 -0800
Kees Cook <kees.cook@...onical.com> wrote:

> In an effort to reduce kernel address leaks that might be used to
> help target kernel privilege escalation exploits, this patch uses
> %pK when displaying addresses in /proc/kallsyms, /proc/modules, and
> /sys/module/*/sections/*.
> 
> Note that this changes %x to %p, so some legitimately 0 values in
> /proc/kallsyms would have changed from 00000000 to "(null)". To avoid
> this, "(null)" is not used when using the "K" format. Anything that was
> already successfully parsing "(null)" in addition to full hex digits
> should have no problem with this change. (Thanks to Joe Perches for
> the suggestion.)
> 
> ...
>
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -477,12 +477,10 @@ static int s_show(struct seq_file *m, void *p)
>  		 */
>  		type = iter->exported ? toupper(iter->type) :
>  					tolower(iter->type);
> -		seq_printf(m, "%0*lx %c %s\t[%s]\n",
> -			   (int)(2 * sizeof(void *)),
> +		seq_printf(m, "%pK %c %s\t[%s]\n",
>  			   iter->value, type, iter->name, iter->module_name);
>  	} else
> -		seq_printf(m, "%0*lx %c %s\n",
> -			   (int)(2 * sizeof(void *)),
> +		seq_printf(m, "%pK %c %s\n",
>  			   iter->value, iter->type, iter->name);
>  	return 0;
>  }

kernel/kallsyms.c: In function 's_show':
kernel/kallsyms.c:481: warning: format '%p' expects type 'void *', but argument 3 has type 'long unsigned int'
kernel/kallsyms.c:484: warning: format '%p' expects type 'void *', but argument 3 has type 'long unsigned int'
kernel/module.c: In function 'module_sect_show':
kernel/module.c:1171: warning: format '%p' expects type 'void *', but argument 3 has type 'long unsigned int'
kernel/module.c:1171: warning: format '%p' expects type 'void *', but argument 3 has type 'long unsigned int'

I'm struggling to see how this could have been compile-time or runtime
tested?

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