linux-hardening - Re: [bug report] clk: visconti: Add support common clock driver and reset driver

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Message-ID: <aTknCZRscyltxAri@stanley.mountain>
Date: Wed, 10 Dec 2025 10:53:45 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: linux-hardening@...r.kernel.org,
	Nobuhiro Iwamatsu <nobuhiro.iwamatsu.x90@...l.toshiba>,
	llvm@...ts.linux.dev
Subject: Re: [bug report] clk: visconti: Add support common clock driver and
 reset driver

On Wed, Dec 10, 2025 at 04:36:11PM +0900, Nathan Chancellor wrote:
> Hey Dan,
> 
> On Tue, Dec 09, 2025 at 04:05:58PM +0300, Dan Carpenter wrote:
> > Hello Kernel Hardenning developers,
> > 
> > Commit b4cbe606dc36 ("clk: visconti: Add support common clock driver
> > and reset driver") from Oct 25, 2021 (linux-next), leads to the
> > question:
> > 
> > drivers/clk/visconti/clkc.c
> >     187 struct visconti_clk_provider *visconti_init_clk(struct device *dev,
> >     188                                                 struct regmap *regmap,
> >     189                                                 unsigned long nr_clks)
> >     190 {
> >     191         struct visconti_clk_provider *ctx;
> >     192         int i;
> >     193 
> >     194         ctx = devm_kzalloc(dev, struct_size(ctx, clk_data.hws, nr_clks), GFP_KERNEL);
> >     195         if (!ctx)
> >     196                 return ERR_PTR(-ENOMEM);
> >     197 
> >     198         for (i = 0; i < nr_clks; ++i)
> > --> 199                 ctx->clk_data.hws[i] = ERR_PTR(-ENOENT);
> >     200         ctx->clk_data.num = nr_clks;
> > 
> > ctx->clk_data.hws[] is __counted_by() ctx->clk_data.num.  Don't we have to
> > set the .num before we fill initialize the array?  Or does the checker
> 
> Yes, it looks like line 200 needs to be moved above line 198.
> 
> > code allow us to access the array when the counted by variable is zero?
> 
> Nope, I just had to fix an instance where num is one and hws[0] is being
> accessed:
> 
>   https://lore.kernel.org/20251124-exynos-clkout-fix-ubsan-bounds-error-v1-1-224a5282514b@kernel.org/
> 
> I suspect there will eventually be a report on real hardware when
> CONFIG_UBSAN_BOUNDS is enabled and GCC 15 is used to build the running
> kernel, which is the first version that supports __counted_by(). How did
> you find this? A new smatch check?

Yeah, but it was a bug in my check.  I need to add __counted_by()
support to Sparse.  If I had that, it would easy enough to add a
warning for places which access the array before setting the counted
by variable.

regards,
carpenter