Message-ID: <202310021107.9BB46FB8E@keescook>
Date:   Mon, 2 Oct 2023 11:08:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian König 
        <ckoenig.leichtzumerken@...il.com>
Cc:     Alex Deucher <alexdeucher@...il.com>,
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        John Harrison <john.c.harrison@...el.com>,
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        Alex Deucher <alexander.deucher@....com>,
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        Christian König <christian.koenig@....com>,
        Zack Rusin <zackr@...are.com>, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 0/9] drm: Annotate structs with __counted_by

On Mon, Oct 02, 2023 at 08:01:57PM +0200, Christian König wrote:
> Am 02.10.23 um 18:53 schrieb Kees Cook:
> > On Mon, Oct 02, 2023 at 11:06:19AM -0400, Alex Deucher wrote:
> > > On Mon, Oct 2, 2023 at 5:20 AM Christian König
> > > <ckoenig.leichtzumerken@...il.com> wrote:
> > > > Am 29.09.23 um 21:33 schrieb Kees Cook:
> > > > > On Fri, 22 Sep 2023 10:32:05 -0700, Kees Cook wrote:
> > > > > > This is a batch of patches touching drm for preparing for the coming
> > > > > > implementation by GCC and Clang of the __counted_by attribute. Flexible
> > > > > > array members annotated with __counted_by can have their accesses
> > > > > > bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS (for array
> > > > > > indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family functions).
> > > > > > 
> > > > > > As found with Coccinelle[1], add __counted_by to structs that would
> > > > > > benefit from the annotation.
> > > > > > 
> > > > > > [...]
> > > > > Since this got Acks, I figure I should carry it in my tree. Let me know
> > > > > if this should go via drm instead.
> > > > > 
> > > > > Applied to for-next/hardening, thanks!
> > > > > 
> > > > > [1/9] drm/amd/pm: Annotate struct smu10_voltage_dependency_table with __counted_by
> > > > >         https://git.kernel.org/kees/c/a6046ac659d6
> > > > STOP! In a follow up discussion Alex and I figured out that this won't work.
> > I'm so confused; from the discussion I saw that Alex said both instances
> > were false positives?
> > 
> > > > The value in the structure is byte swapped based on some firmware
> > > > endianness which not necessary matches the CPU endianness.
> > > SMU10 is APU only so the endianess of the SMU firmware and the CPU
> > > will always match.
> > Which I think is what is being said here?
> > 
> > > > Please revert that one from going upstream if it's already on it's way.
> > > > 
> > > > And because of those reasons I strongly think that patches like this
> > > > should go through the DRM tree :)
> > Sure, that's fine -- please let me know. It was others Acked/etc. Who
> > should carry these patches?
> 
> Probably best if the relevant maintainer pick them up individually.
> 
> Some of those structures are filled in by firmware/hardware and only the
> maintainers can judge if that value actually matches what the compiler
> needs.
> 
> We have cases where individual bits are used as flags or when the size is
> byte swapped etc...
> 
> Even Alex and I didn't immediately say how and where that field is actually
> used and had to dig that up. That's where the confusion came from.

Okay, I've dropped them all from my tree. Several had Acks/Reviews, so
hopefully those can get picked up for the DRM tree?

Thanks!

-Kees

-- 
Kees Cook

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