Re: [PATCH] rtc: ac100: Assign .num before accessing .hws

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 9/6/26 03:38, Aamir Ahmed 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 ac100_rtc_register_clks() due to .num being assigned only
> after every clkout clock has been stored in .hws[]. With
> CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC
> 15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report
> during probe, and with CONFIG_UBSAN_TRAP the first store traps.
> 
> Initialize .num with AC100_CLKOUT_NUM, the number of elements .hws[] was
> allocated with, right after the allocation. That is the value the loop
> counter ends up at on the success path anyway, so the provider's
> behaviour is unchanged.
> 
> Cc: stable@vger.kernel.org
> Fixes: f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by")
> Assisted-by: LLM
> Signed-off-by: Aamir Ahmed <elb12345@hotmail.co.uk>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks
-Gustavo

> ---
> Found while auditing the remaining clk_hw_onecell_data users that assign
> .num only after touching .hws[], following the fixes already merged for
> clk-s2mps11 (3e14c7207a97), exynos-clkout (cf33f0b7df13) and
> clk-raspberrypi (6dc445c19050). The audit, the fix and this changelog
> were drafted with an LLM assistant and reviewed by hand.
> 
> Compile-tested only (W=1, no warnings) on x86_64 with GCC 13.3, with
> CONFIG_RTC_DRV_AC100=m forced on the make command line because the
> driver has no COMPILE_TEST option. GCC 13.3 does not implement
> __counted_by (CC_HAS_COUNTED_BY needs GCC 15.1+ or Clang 20.1+), so the
> build only confirms that the change compiles; the sanitizer path was not
> exercised. I do not have the hardware, so this is not runtime-tested and
> no UBSAN report was captured.
> 
> Based on v7.3-rc1.
> 
>   drivers/rtc/rtc-ac100.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/rtc/rtc-ac100.c b/drivers/rtc/rtc-ac100.c
> index bba7115ff3a..a2f465438fd 100644
> --- a/drivers/rtc/rtc-ac100.c
> +++ b/drivers/rtc/rtc-ac100.c
> @@ -317,6 +317,8 @@ static int ac100_rtc_register_clks(struct ac100_rtc_dev *chip)
>   	if (!chip->clk_data)
>   		return -ENOMEM;
>   
> +	chip->clk_data->num = AC100_CLKOUT_NUM;
> +
>   	chip->rtc_32k_clk = clk_hw_register_fixed_rate(chip->dev,
>   						       AC100_RTC_32K_NAME,
>   						       NULL, 0,
> @@ -360,7 +362,6 @@ static int ac100_rtc_register_clks(struct ac100_rtc_dev *chip)
>   		chip->clk_data->hws[i] = &clk->hw;
>   	}
>   
> -	chip->clk_data->num = i;
>   	ret = of_clk_add_hw_provider(np, of_clk_hw_onecell_get, chip->clk_data);
>   	if (ret)
>   		goto err_unregister_rtc_32k;
> 
> base-commit: 654ae5d73c05bd2943d65636ce6cd0aa46e62f18