From: Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: miles.chen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org
Cc: Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
wsd_upstream-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org,
Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Pekka Enberg <penberg-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
Christoph Lameter <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>,
Joonsoo Kim <iamjoonsoo.kim-Hm3cg6mZ9cc@public.gmane.org>,
"Tobin C . Harding" <me-xzjC0nNlxno@public.gmane.org>
Subject: Re: [RFC PATCH v2] mm: slub: print kernel addresses in slub debug messages
Date: Thu, 8 Aug 2019 19:46:44 -0700 [thread overview]
Message-ID: <20190809024644.GL5482@bombadil.infradead.org> (raw)
In-Reply-To: <20190809010837.24166-1-miles.chen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org wrote:
> Possible approaches are:
> 1. stop printing kernel addresses
> 2. print with %pK,
> 3. print with %px.
No. The point of obscuring kernel addresses is that if the attacker manages to find a way to get the kernel to spit out some debug messages that we shouldn't
leak all this extra information.
> 4. do nothing
5. Find something more useful to print.
> INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____)
... you don't have any randomness on your platform?
> INFO: Object 0x(____ptrval____) @offset=1408 fp=0x(____ptrval____)
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5
> Redzone (____ptrval____): bb bb bb bb bb bb bb bb
> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> ...
> FIX kmalloc-128: Object at 0x(____ptrval____) not freed
But if you have randomness, at least some of these "pointers" are valuable
because you can compare them against "pointers" printed by other parts
of the kernel.
> After this patch:
>
> INFO: Slab 0xffffffbf00f57000 objects=25 used=23 fp=0xffffffc03d5c3500
> INFO: Object 0xffffffc03d5c3500 @offset=13568 fp=0xffffffc03d5c0800
> Redzone 00000000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000020: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000030: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000040: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000050: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000060: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Redzone 00000070: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb
> Object 00000000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000020: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000030: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000040: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000050: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000060: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Object 00000070: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5
> Redzone 00000000: bb bb bb bb bb bb bb bb
> Padding 00000000: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> Padding 00000010: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> Padding 00000020: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> Padding 00000030: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a
> ...
> FIX kmalloc-128: Object at 0xffffffc03d5c3500 not freed
It looks prettier, but I'm not convinced it's more useful. Unless your
platform lacks randomness ...
next prev parent reply other threads:[~2019-08-09 2:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 1:08 [RFC PATCH v2] mm: slub: print kernel addresses in slub debug messages miles.chen
[not found] ` <20190809010837.24166-1-miles.chen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
2019-08-09 2:46 ` Matthew Wilcox [this message]
2019-08-09 14:11 ` Miles Chen
2019-08-09 14:26 ` Matthew Wilcox
2019-08-12 8:24 ` Miles Chen
2019-08-12 13:32 ` Vlastimil Babka
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