linux-hardening - Re: [PATCH] thermal: core: Move initial num

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Message-ID: <202402280944.CE26D81@keescook>
Date: Wed, 28 Feb 2024 09:48:26 -0800
From: Kees Cook <keescook@...omium.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Lukasz Luba <lukasz.luba@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>, rui.zhang@...el.com,
	gustavoars@...nel.org, morbo@...gle.com, justinstitt@...gle.com,
	stanislaw.gruszka@...ux.intel.com, linux-pm@...r.kernel.org,
	linux-hardening@...r.kernel.org, llvm@...ts.linux.dev,
	patches@...ts.linux.dev, Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH] thermal: core: Move initial num_trips assignment before
 memcpy()

On Wed, Feb 28, 2024 at 09:56:51AM -0700, Nathan Chancellor wrote:
> On Wed, Feb 28, 2024 at 08:41:07AM +0000, Lukasz Luba wrote:
> > Hi Nathan and Kees,
> > 
> > On 2/27/24 17:00, Kees Cook wrote:
> > > On Tue, Feb 27, 2024 at 05:47:44PM +0100, Daniel Lezcano wrote:
> > > > Ok my misunderstanding was I thought sizeof() was calling _bdos under the
> > > > hood, so when calling sizeof(flex_array), it was returning the computed size
> > > > inferring from the __counted_by field.
> > > 
> > > Yeah, sizeof() has a very limited scope. __builtin_object_size() has
> > > more flexibility (via the 2nd argument, "type"), but it was still
> > > compile-time only. __builtin_dynamic_object_size() was added to bring
> > > runtime evaluations into the mix (initially to support the alloc_size
> > > attribute, and now includes the counted_by attribute too).
> > > 
> > 
> > Thanks for your earlier emails explaining these stuff.
> > Do you have maybe some presentation about those features
> > for the kernel (ideally w/ a video from some conference)?
> 
> I think Kees's 2022 and 2023 talks at LPC are a good place to start:
> 
> https://youtu.be/tQwv79i02ks?si=Nj9hpvmQwPB4K3Y4&t=452
> https://youtu.be/OEFFqhP5sts?si=u6RnOP641S8FkouD&t=614
> 
> https://outflux.net/slides/2022/lpc/features.pdf
> https://outflux.net/slides/2023/lpc/features.pdf

I've also got a write-up on the entire topic of array bounds, which ends
with some discussion of "the future" (which is now) involving the use of
the "counted_by" attribute:
https://people.kernel.org/kees/bounded-flexible-arrays-in-c#coming-soon-annotate-bounds-of-flexible-arrays

-- 
Kees Cook