linux-kernel - Re: [PATCH] clk: samsung: exynos-clkout: Assign .num before accessing .hws

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Message-ID: <CAPLW+4k=My6np3uKoRmODDVbUekTs+yDdBbwoH_Ba743sRQTRg@mail.gmail.com>
Date: Mon, 24 Nov 2025 14:51:42 -0600
From: Sam Protsenko <semen.protsenko@...aro.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Sylwester Nawrocki <s.nawrocki@...sung.com>, 
	Chanwoo Choi <cw00.choi@...sung.com>, Alim Akhtar <alim.akhtar@...sung.com>, 
	Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Salvatore Bonaccorso <carnil@...ian.org>, 
	linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, stable@...r.kernel.org, 
	Jochen Sprickerhof <jochen@...ickerhof.de>
Subject: Re: [PATCH] clk: samsung: exynos-clkout: Assign .num before accessing .hws

On Mon, Nov 24, 2025 at 1:11 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with
> __counted_by") annotated the hws member of 'struct clk_hw_onecell_data'
> with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS)
> about the number of elements in .hws[], so that it can warn when .hws[]
> is accessed out of bounds. As noted in that change, the __counted_by
> member must be initialized with the number of elements before the first
> array access happens, otherwise there will be a warning from each access
> prior to the initialization because the number of elements is zero. This
> occurs in exynos_clkout_probe() due to .num being assigned after .hws[]
> has been accessed:
>
>   UBSAN: array-index-out-of-bounds in drivers/clk/samsung/clk-exynos-clkout.c:178:18
>   index 0 is out of range for type 'clk_hw *[*]'
>
> Move the .num initialization to before the first access of .hws[],
> clearing up the warning.
>
> Cc: stable@...r.kernel.org
> Fixes: f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
> Reported-by: Jochen Sprickerhof <jochen@...ickerhof.de>
> Closes: https://lore.kernel.org/aSIYDN5eyKFKoXKL@eldamar.lan/
> Tested-by: Jochen Sprickerhof <jochen@...ickerhof.de>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---

Reviewed-by: Sam Protsenko <semen.protsenko@...aro.org>

>  drivers/clk/samsung/clk-exynos-clkout.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/clk/samsung/clk-exynos-clkout.c b/drivers/clk/samsung/clk-exynos-clkout.c
> index 5f1a4f5e2e59..5b21025338bd 100644
> --- a/drivers/clk/samsung/clk-exynos-clkout.c
> +++ b/drivers/clk/samsung/clk-exynos-clkout.c
> @@ -175,6 +175,7 @@ static int exynos_clkout_probe(struct platform_device *pdev)
>         clkout->mux.shift = EXYNOS_CLKOUT_MUX_SHIFT;
>         clkout->mux.lock = &clkout->slock;
>
> +       clkout->data.num = EXYNOS_CLKOUT_NR_CLKS;
>         clkout->data.hws[0] = clk_hw_register_composite(NULL, "clkout",
>                                 parent_names, parent_count, &clkout->mux.hw,
>                                 &clk_mux_ops, NULL, NULL, &clkout->gate.hw,
> @@ -185,7 +186,6 @@ static int exynos_clkout_probe(struct platform_device *pdev)
>                 goto err_unmap;
>         }
>
> -       clkout->data.num = EXYNOS_CLKOUT_NR_CLKS;
>         ret = of_clk_add_hw_provider(clkout->np, of_clk_hw_onecell_get, &clkout->data);
>         if (ret)
>                 goto err_clk_unreg;
>
> ---
> base-commit: b6430552c8cd95e90bb842ce2f421e7a5381859f
> change-id: 20251124-exynos-clkout-fix-ubsan-bounds-error-93071375ec78
>
> Best regards,
> --
> Nathan Chancellor <nathan@...nel.org>
>
>