linux-kernel - Re: [PATCH 2/2] kasan: apply store-only mode in kasan kunit testcases

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Message-ID: <aJuxuKBm9qfpVkBC@e129823.arm.com>
Date: Tue, 12 Aug 2025 22:27:20 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: ryabinin.a.a@...il.com, glider@...gle.com, dvyukov@...gle.com,
	vincenzo.frascino@....com, corbet@....net, catalin.marinas@....com,
	will@...nel.org, akpm@...ux-foundation.org,
	scott@...amperecomputing.com, jhubbard@...dia.com,
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	maz@...nel.org, broonie@...nel.org, oliver.upton@...ux.dev,
	james.morse@....com, ardb@...nel.org,
	hardevsinh.palaniya@...iconsignals.io, david@...hat.com,
	yang@...amperecomputing.com, kasan-dev@...glegroups.com,
	workflows@...r.kernel.org, linux-doc@...r.kernel.org,
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	linux-mm@...ck.org
Subject: Re: [PATCH 2/2] kasan: apply store-only mode in kasan kunit testcases

Hi Andrey,
> >
> > > Right now, KASAN tests are crafted to avoid/self-contain harmful
> > > memory corruptions that they do (e.g. make sure that OOB write
> > > accesses land in in-object kmalloc training space, etc.). If you turn
> > > read accesses in tests into write accesses, memory corruptions caused
> > > by the earlier tests will crash the kernel or the latter tests.
> >
> > That's why I run the store-only test when this mode is "sync"
> > In case of "async/asymm" as you mention since it reports "after",
> > there will be memory corruption.
> >
> > But in case of sync, when the MTE fault happens, it doesn't
> > write to memory so, I think it's fine.
>
> Does it not? I thought MTE gets disabled and we return from the fault
> handler and let the write instruction execute. But my memory on this
> is foggy. And I don't have a setup right now to test.

Right. when fault is hit the MTE gets disabled.
But in kasan_test_c.c -- See the KUNIT_EXPECT_KASAN_FAIL,
It re-enables for next test by calling kasan_enable_hw_tags().

So, the store-only with sync mode seems fine unless we wouldn't care
about failure (no fault happen) which makes memory corruption.

However, I'm not sure writing the seperate testcases for store-only
is right or now since
same tests which only are different of return value check will be
duplicate and half of these always skipped (when duplicate for
store-only, former should be skip and vice versa).

Thanks.

--
Sincerely,
Yeoreum Yun