linux-kernel - Re: [PATCH v4] mm, kasan, kmsan: copy_from/to_kernel

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Message-ID: <CANpmjNO9js1Ncb9b=wQQCJi4K8XZEDf_Z9E29yw2LmXkOdH0Xw@mail.gmail.com>
Date: Tue, 8 Oct 2024 21:34:10 +0200
From: Marco Elver <elver@...gle.com>
To: Sabyrzhan Tasbolatov <snovitoll@...il.com>
Cc: akpm@...ux-foundation.org, andreyknvl@...il.com, bpf@...r.kernel.org, 
	dvyukov@...gle.com, glider@...gle.com, kasan-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, ryabinin.a.a@...il.com, 
	syzbot+61123a5daeb9f7454599@...kaller.appspotmail.com, 
	vincenzo.frascino@....com
Subject: Re: [PATCH v4] mm, kasan, kmsan: copy_from/to_kernel_nofault

On Tue, 8 Oct 2024 at 21:28, Sabyrzhan Tasbolatov <snovitoll@...il.com> wrote:
>
> Instrument copy_from_kernel_nofault() with KMSAN for uninitialized kernel
> memory check and copy_to_kernel_nofault() with KASAN, KCSAN to detect
> the memory corruption.
>
> syzbot reported that bpf_probe_read_kernel() kernel helper triggered
> KASAN report via kasan_check_range() which is not the expected behaviour
> as copy_from_kernel_nofault() is meant to be a non-faulting helper.
>
> Solution is, suggested by Marco Elver, to replace KASAN, KCSAN check in
> copy_from_kernel_nofault() with KMSAN detection of copying uninitilaized
> kernel memory. In copy_to_kernel_nofault() we can retain
> instrument_write() explicitly for the memory corruption instrumentation.
>
> copy_to_kernel_nofault() is tested on x86_64 and arm64 with
> CONFIG_KASAN_SW_TAGS. On arm64 with CONFIG_KASAN_HW_TAGS,
> kunit test currently fails. Need more clarification on it
> - currently, disabled in kunit test.
>
> Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@mail.gmail.com/
> Reviewed-by: Marco Elver <elver@...gle.com>
> Reported-by: syzbot+61123a5daeb9f7454599@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
> Reported-by: Andrey Konovalov <andreyknvl@...il.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@...il.com>
> ---
> v2:
> - squashed previous submitted in -mm tree 2 patches based on Linus tree
> v3:
> - moved checks to *_nofault_loop macros per Marco's comments
> - edited the commit message
> v4:
> - replaced Suggested-By with Reviewed-By: Marco Elver

For future reference: No need to send v+1 just for this tag. Usually
maintainers pick up tags from the last round without the original
author having to send out a v+1 with the tags. Of course, if you make
other corrections and need to send a v+1, then it is appropriate to
collect tags where those tags would remain valid (such as on unchanged
patches part of the series, or for simpler corrections).