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

Dan Carpenter
2025-12-10T07:53:52Z

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