Message-ID: <202310050915.ABB0419C@keescook>
Date:   Thu, 5 Oct 2023 09:16:21 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian König 
        <ckoenig.leichtzumerken@...il.com>
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        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 0/9] drm: Annotate structs with __counted_by

On Thu, Oct 05, 2023 at 11:42:38AM +0200, Christian König wrote:
> Am 02.10.23 um 20:22 schrieb Kees Cook:
> > On Mon, Oct 02, 2023 at 08:11:41PM +0200, Christian König wrote:
> > > Am 02.10.23 um 20:08 schrieb Kees Cook:
> > > > 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?
> > > I will pick those up to go through drm-misc-next.
> > > 
> > > Going to ping maintainers once more when I'm not sure if stuff is correct or
> > > not.
> > Sounds great; thanks!
> 
> I wasn't 100% sure for the VC4 patch, but pushed the whole set to
> drm-misc-next anyway.
> 
> This also means that the patches are now auto merged into the drm-tip
> integration branch and should any build or unit test go boom we should
> notice immediately and can revert it pretty easily.

Thanks very much; I'll keep an eye out for any reports.

-- 
Kees Cook

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