linux-kernel - Re: [PATCH] clk: spacemit: fix UBSAN warning during probe

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Message-ID: <d74628b6-9441-4853-9c47-6fffe8d654e6@riscstar.com>
Date: Mon, 17 Nov 2025 13:13:44 -0600
From: Alex Elder <elder@...cstar.com>
To: Charles Mirabile <cmirabil@...hat.com>, linux-kernel@...r.kernel.org
Cc: spacemit@...ts.linux.dev, linux-riscv@...ts.infradead.org,
 linux-clk@...r.kernel.org, mturquette@...libre.com, sboyd@...nel.org,
 dlan@...too.org, heylenay@....org, troy.mitchell@...ux.spacemit.com,
 inochiama@...look.com, Yanko Kaneti <yaneti@...lera.com>
Subject: Re: [PATCH] clk: spacemit: fix UBSAN warning during probe

On 11/17/25 1:03 PM, Charles Mirabile wrote:
> When booting with KASAN enabled the following splat is encountered during
> probe of the k1 clock driver:
> 
> UBSAN: array-index-out-of-bounds in drivers/clk/spacemit/ccu-k1.c:1044:16
> index 0 is out of range for type 'clk_hw *[*]'
> CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.18.0-rc5+ #1 PREEMPT(lazy)
> Hardware name: Unknown Unknown Product/Unknown Product, BIOS 2022.10spacemit 10/01/2022
> Call Trace:
> [<ffffffff8002b628>] dump_backtrace+0x28/0x38
> [<ffffffff800027d2>] show_stack+0x3a/0x50
> [<ffffffff800220c2>] dump_stack_lvl+0x5a/0x80
> [<ffffffff80022100>] dump_stack+0x18/0x20
> [<ffffffff800164b8>] ubsan_epilogue+0x10/0x48
> [<ffffffff8099034e>] __ubsan_handle_out_of_bounds+0xa6/0xa8
> [<ffffffff80acbfa6>] k1_ccu_probe+0x37e/0x420
> [<ffffffff80b79e6e>] platform_probe+0x56/0x98
> [<ffffffff80b76a7e>] really_probe+0x9e/0x350
> [<ffffffff80b76db0>] __driver_probe_device+0x80/0x138
> [<ffffffff80b76f52>] driver_probe_device+0x3a/0xd0
> [<ffffffff80b771c4>] __driver_attach+0xac/0x1b8
> [<ffffffff80b742fc>] bus_for_each_dev+0x6c/0xc8
> [<ffffffff80b76296>] driver_attach+0x26/0x38
> [<ffffffff80b759ae>] bus_add_driver+0x13e/0x268
> [<ffffffff80b7836a>] driver_register+0x52/0x100
> [<ffffffff80b79a78>] __platform_driver_register+0x28/0x38
> [<ffffffff814585da>] k1_ccu_driver_init+0x22/0x38
> [<ffffffff80023a8a>] do_one_initcall+0x62/0x2a0
> [<ffffffff81401c60>] do_initcalls+0x170/0x1a8
> [<ffffffff81401e7a>] kernel_init_freeable+0x16a/0x1e0
> [<ffffffff811f7534>] kernel_init+0x2c/0x180
> [<ffffffff80025f56>] ret_from_fork_kernel+0x16/0x1d8
> [<ffffffff81205336>] ret_from_fork_kernel_asm+0x16/0x18
> ---[ end trace ]---
> 
> This is bogus and is simply a result of KASAN consulting the `.num` member
> of the struct for bounds information (as it should due to `__counted_by`)
> and finding 0 set by kzalloc because it has not been initialized before
> the loop that fills in the array. The easy fix is to just move the line
> that sets `num` to before the loop that fills the array so that KASAN has
> the information it needs to accurately conclude that the access is valid.
> 
> 
> Fixes: 1b72c59db0add ("clk: spacemit: Add clock support for SpacemiT K1 SoC")
> Tested-by: Yanko Kaneti <yaneti@...lera.com>
> 
> Signed-off-by: Charles Mirabile <cmirabil@...hat.com>

Looks good to me.  I haven't used UBSAN but the report is clearly
complaining about exactly what you describe.  Your fix seems like
exactly the right thing to do.

Reviewed-by: Alex Elder <elder@...cstar.com>

> ---
>   drivers/clk/spacemit/ccu-k1.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/spacemit/ccu-k1.c b/drivers/clk/spacemit/ccu-k1.c
> index f5a9fe6ba1859..4761bc1e3b6e6 100644
> --- a/drivers/clk/spacemit/ccu-k1.c
> +++ b/drivers/clk/spacemit/ccu-k1.c
> @@ -1018,6 +1018,8 @@ static int spacemit_ccu_register(struct device *dev,
>   	if (!clk_data)
>   		return -ENOMEM;
>   
> +	clk_data->num = data->num;
> +
>   	for (i = 0; i < data->num; i++) {
>   		struct clk_hw *hw = data->hws[i];
>   		struct ccu_common *common;
> @@ -1044,8 +1046,6 @@ static int spacemit_ccu_register(struct device *dev,
>   		clk_data->hws[i] = hw;
>   	}
>   
> -	clk_data->num = data->num;
> -
>   	ret = devm_of_clk_add_hw_provider(dev, of_clk_hw_onecell_get, clk_data);
>   	if (ret)
>   		dev_err(dev, "failed to add clock hardware provider (%d)\n", ret);
> 
> base-commit: 6a23ae0a96a600d1d12557add110e0bb6e32730c