linux-kernel - Re: [PATCH v3 1/2] kasan: catch invalid free before SLUB reinitializes the object

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Message-ID: <CA+fCnZckG1Ww9wNcXRuCwdovK5oW3dq98Uq4up-WYOmddA9icA@mail.gmail.com>
Date: Sat, 27 Jul 2024 02:47:07 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Jann Horn <jannh@...gle.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, 
	Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, 
	Joonsoo Kim <iamjoonsoo.kim@....com>, Vlastimil Babka <vbabka@...e.cz>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>, 
	Marco Elver <elver@...gle.com>, kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v3 1/2] kasan: catch invalid free before SLUB
 reinitializes the object

On Fri, Jul 26, 2024 at 3:52 PM Jann Horn <jannh@...gle.com> wrote:
>
> > Do we still need this patch?
>
> I just tried removing this patch from the series; without it, the
> kmem_cache_invalid_free kunit test fails because the kmem_cache_free()
> no longer synchronously notices that the pointer is misaligned. I
> guess I could change the testcase like this to make the tests pass
> without this patch, but I'd like to hear from you or another KASAN
> person whether you think that's a reasonable change:

Ah, I see. I think detecting a bug earlier if we can is better. So I
don't mind keeping this patch, was just confused by the commit
message.

Adding on top of my comments from before: I think if you move
check_slab_free() out of poison_slab_object() (but add to
__kasan_mempool_poison_object()), and move is_kfence_address() and
kasan_arch_is_ready() to poison_slab_object()'s callers, you won't
even need the free_validation_result enum, so the patch should become
simpler.

You can also rename check_slab_free() to check_slab_allocation() to
make it be named similarly to the already existing
check_page_allocation(). (I think we should also later move
kasan_arch_is_ready() out of check_page_allocation() into the
high-level hooks for consistency; it also seems cleaner to have all of
these ignore checks in the high-level functions instead of lower-level
inlined ones.)

Thanks!