From: Matthew Wilcox <willy@infradead.org>
To: miles.chen@mediatek.com
Cc: Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
"Tobin C . Harding" <me@tobin.cc>,
Kees Cook <keescook@chromium.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@mediatek.com>
On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@mediatek.com 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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190809024644.GL5482@bombadil.infradead.org \
--to=willy@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=cl@linux.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mediatek@lists.infradead.org \
--cc=linux-mm@kvack.org \
--cc=me@tobin.cc \
--cc=miles.chen@mediatek.com \
--cc=penberg@kernel.org \
--cc=rientjes@google.com \
--cc=wsd_upstream@mediatek.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).