linux-kernel - Re: [PATCH v2 RFC 1/7] mm/kasan: implement kasan_poison

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Message-ID: <CANgxf6wziVLi5F5ZoF2nwGhoCyLhk5YJ_MBtHaCaGtuzFky_Vw@mail.gmail.com>
Date: Fri, 5 Sep 2025 10:46:11 +0200
From: Ethan Graham <ethan.w.s.graham@...il.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: ethangraham@...gle.com, andreyknvl@...il.com, brendan.higgins@...ux.dev, 
	davidgow@...gle.com, dvyukov@...gle.com, jannh@...gle.com, elver@...gle.com, 
	rmoar@...gle.com, shuah@...nel.org, tarasmadan@...gle.com, 
	kasan-dev@...glegroups.com, kunit-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, dhowells@...hat.com, 
	lukas@...ner.de, ignat@...udflare.com, herbert@...dor.apana.org.au, 
	davem@...emloft.net, linux-crypto@...r.kernel.org
Subject: Re: [PATCH v2 RFC 1/7] mm/kasan: implement kasan_poison_range

On Fri, Sep 5, 2025 at 10:33 AM Alexander Potapenko <glider@...gle.com> wrote:
> > + * - The poisoning of the range only extends up to the last full granule before
> > + *     the end of the range. Any remaining bytes in a final partial granule are
> > + *     ignored.
>
> Maybe we should require that the end of the range is aligned, as we do
> for e.g. kasan_unpoison()?
> Are there cases in which we want to call it for non-aligned addresses?

It's possible in the current KFuzzTest input format. For example you have
an 8 byte struct with a pointer to a 35-byte string. This results in a payload:
struct [0: 8), padding [8: 16), string: [16: 51), padding: [51: 59). The
framework will poison the unaligned region [51, 59).

We could enforce that the size of the payload (including all padding) is
a multiple of KASAN_GRANULE_SIZE, thus resulting in padding [51, 64)
at the end of the payload. It makes encoding a bit more complex, but it
may be a good idea to push that complexity up to the user space encoder.

What do you think?