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

Nathan Chancellor
2025-12-10T07:36:15Z

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? It would be nice if the compilers
could flag this but I guess it is probably harder to do this in a
generic way.

Cheers,
Nathan