linux-kernel - Re: [PATCH v1 03/10] kfuzztest: implement core module and input processing

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Message-ID: <CAG_fn=U0dOBumngmQQ1cna=SZvbDXjJ8NrVUZyCHY5dzJV4rVg@mail.gmail.com>
Date: Tue, 16 Sep 2025 12:21:31 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Ethan Graham <ethan.w.s.graham@...il.com>
Cc: ethangraham@...gle.com, andreyknvl@...il.com, andy@...nel.org, 
	brauner@...nel.org, brendan.higgins@...ux.dev, davem@...emloft.net, 
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	elver@...gle.com, herbert@...dor.apana.org.au, ignat@...udflare.com, 
	jack@...e.cz, jannh@...gle.com, johannes@...solutions.net, 
	kasan-dev@...glegroups.com, kees@...nel.org, kunit-dev@...glegroups.com, 
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, lukas@...ner.de, rmoar@...gle.com, shuah@...nel.org, 
	tarasmadan@...gle.com
Subject: Re: [PATCH v1 03/10] kfuzztest: implement core module and input processing

On Tue, Sep 16, 2025 at 11:01 AM Ethan Graham
<ethan.w.s.graham@...il.com> wrote:
>
> From: Ethan Graham <ethangraham@...gle.com>
>
> Add the core runtime implementation for KFuzzTest. This includes the
> module initialization, and the logic for receiving and processing
> user-provided inputs through debugfs.
>
> On module load, the framework discovers all test targets by iterating
> over the .kfuzztest_target section, creating a corresponding debugfs
> directory with a write-only 'input' file for each of them.
>
> Writing to an 'input' file triggers the main fuzzing sequence:
> 1. The serialized input is copied from userspace into a kernel buffer.
> 2. The buffer is parsed to validate the region array and relocation
>    table.
> 3. Pointers are patched based on the relocation entries, and in KASAN
>    builds the inter-region padding is poisoned.
> 4. The resulting struct is passed to the user-defined test logic.
>
> Signed-off-by: Ethan Graham <ethangraham@...gle.com>
>
> ---
> v3:

Nit: these are RFC version numbers, and they will start clashing with
the non-RFC numbers next time you update this series.
I suggest changing them to "RFC v3" and "RFC v2" respectively.

> +
> +/**
> + * kfuzztest_init - initializes the debug filesystem for KFuzzTest
> + *
> + * Each registered target in the ".kfuzztest_targets" section gets its own
> + * subdirectory under "/sys/kernel/debug/kfuzztest/<test-name>" containing one
> + * write-only "input" file used for receiving inputs from userspace.
> + * Furthermore, a directory "/sys/kernel/debug/kfuzztest/_config" is created,
> + * containing two read-only files "minalign" and "num_targets", that return
> + * the minimum required region alignment and number of targets respectively.

This comment (and some below) is out of sync with the implementation.
As we've discussed offline, there's probably little value in having
"/sys/kernel/debug/kfuzztest/_config/num_targets", because that number
is equal to the number of files in "/sys/kernel/debug/kfuzztest/"
minus one.
It just came to my mind that "num_invocations" could be moved to some
"kfuzztest/_stat" directory, but it can also stay here as long as you
fix the doc comments.