From: Vlastimil Babka <vbabka@suse.cz>
To: Christopher Lameter <cl@linux.com>, Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Waiman Long <longman@redhat.com>, Marco Elver <elver@google.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Roman Gushchin <guro@fb.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH v3 0/3] Actually fix freelist pointer vs redzoning
Date: Thu, 15 Oct 2020 11:44:15 +0200 [thread overview]
Message-ID: <1e43fd23-e9f1-9c5d-3ee2-17171642877f@suse.cz> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2010150822260.184556@www.lameter.com>
On 10/15/20 10:23 AM, Christopher Lameter wrote:
> On Wed, 14 Oct 2020, Kees Cook wrote:
>
>> Note on patch 2: Christopher NAKed it, but I actually think this is a
>> reasonable thing to add -- the "too small" check is only made when built
>> with CONFIG_DEBUG_VM, so it *is* actually possible for someone to trip
>> over this directly, even if it would never make it into a released
>> kernel. I see no reason to just leave this foot-gun in place, though, so
>> we might as well just fix it too. (Which seems to be what Longman was
>> similarly supporting, IIUC.)
>
> Well then remove the duplication of checks. The NAK was there because it
> seems that you were not aware of the existing checks.
>
>> Anyway, if patch 2 stays NAKed, that's fine. It's entirely separable,
>> and the other 2 can land. :)
>
> Just deal with the old checks too and it will be fine.
Yeah, the existing check is under CONFIG_DEBUG_VM, which means it's not active
on some configurations. Creating a cache is not exactly fast path operation, so
I would remove this guard.
As for the minimum size check, I would probably remove it (but watch out if
SLAB/SLOB can handle it). It's not effective to use slab cache for 4-byte
objects, but why make it an error.
next prev parent reply other threads:[~2020-10-15 9:44 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-15 3:37 Kees Cook
2020-10-15 3:37 ` [PATCH v3 1/3] mm/slub: Clarify verification reporting Kees Cook
2020-10-15 3:37 ` [PATCH v3 2/3] mm/slub: Fix redzoning for small allocations Kees Cook
2020-10-15 3:37 ` [PATCH v3 3/3] mm/slub: Actually fix freelist pointer vs redzoning Kees Cook
2020-10-15 8:23 ` [PATCH v3 0/3] " Christopher Lameter
2020-10-15 9:44 ` Vlastimil Babka [this message]
2020-10-15 22:03 ` Kees Cook
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