From: Stephen Boyd <swboyd@chromium.org>
To: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, Petr Mladek <pmladek@suse.com>,
Joe Perches <joe@perches.com>
Subject: Re: [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug is enabled
Date: Mon, 20 Sep 2021 11:23:01 -0700 [thread overview]
Message-ID: <CAE-0n50v6Wm2OBsy5-Q3B9VrNhH+_uyDDa8Ps3MeXsCLZczW3w@mail.gmail.com> (raw)
In-Reply-To: <202109200726.2EFEDC5@keescook>
Quoting Kees Cook (2021-09-20 07:29:54)
> On Tue, Jun 01, 2021 at 11:22:02AM -0700, Stephen Boyd wrote:
> > Obscuring the pointers that slub shows when debugging makes for some
> > confusing slub debug messages:
> >
> > Padding overwritten. 0x0000000079f0674a-0x000000000d4dce17
> >
> > Those addresses are hashed for kernel security reasons. If we're trying
> > to be secure with slub_debug on the commandline we have some big
> > problems given that we dump whole chunks of kernel memory to the kernel
> > logs. Let's force on the no_hash_pointers commandline flag when
> > slub_debug is on the commandline. This makes slub debug messages more
> > meaningful and if by chance a kernel address is in some slub debug
> > object dump we will have a better chance of figuring out what went
> > wrong.
> >
> > Note that we don't use %px in the slub code because we want to reduce
> > the number of places that %px is used in the kernel. This also nicely
> > prints a big fat warning at kernel boot if slub_debug is on the
> > commandline so that we know that this kernel shouldn't be used on
> > production systems.
>
> Eeeek. I missed this patch. NAK NAK. People use slub_debug for
> production systems to gain redzoning, etc, as a layer of defense, and
> they absolutely do not want %p-hashing disabled. %p hashing is
> controlled by the no_hash_pointers boot param (since v5.12), and needs to stay
> separate from slub_debug.
>
> Can we please revert this in Linus's tree and in v5.14?
>
This is fine with me as long as debugging with slub_debug on the
commandline is possible. Would you prefer v1 of this patch series[1]
that uses the printk format to print unhashed pointers in slub debugging
messages?
[1] https://lore.kernel.org/r/20210520013539.3733631-1-swboyd@chromium.org
next prev parent reply other threads:[~2021-09-20 18:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-01 18:21 [PATCH v3 0/4] slub: Print non-hashed pointers in slub debugging Stephen Boyd
2021-06-01 18:21 ` [PATCH v3 1/4] slub: Restore slub_debug=- behavior Stephen Boyd
2021-06-01 18:22 ` [PATCH v3 2/4] slub: Actually use 'message' in restore_bytes() Stephen Boyd
2021-06-01 18:22 ` [PATCH v3 3/4] slub: Indicate slab_fix() uses printf formats Stephen Boyd
2021-06-06 0:06 ` David Rientjes
2021-06-01 18:22 ` [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug is enabled Stephen Boyd
2021-06-01 22:45 ` kernel test robot
2021-06-02 0:26 ` Andrew Morton
2021-06-02 1:03 ` Stephen Boyd
2021-06-02 10:48 ` Vlastimil Babka
2021-06-02 10:50 ` Vlastimil Babka
2021-06-03 13:15 ` Petr Mladek
2021-09-20 14:29 ` Kees Cook
2021-09-20 18:23 ` Stephen Boyd [this message]
2021-09-20 18:28 ` Kees Cook
2021-09-20 18:44 ` Stephen Boyd
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