linux-kernel - Re: [PATCH v3] clk: mvebu: Prevent division by zero in clk_double_div_recalc

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Message-ID: <af7dc028ced22413210701a5e2e05990.sboyd@kernel.org>
Date: Thu, 19 Sep 2024 03:24:15 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: Alexandra Diupina <adiupina@...ralinux.ru>, Andrew Lunn <andrew@...n.ch>
Cc: Alexandra Diupina <adiupina@...ralinux.ru>, Gregory Clement <gregory.clement@...tlin.com>, Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>, Michael Turquette <mturquette@...libre.com>, linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v3] clk: mvebu: Prevent division by zero in clk_double_div_recalc_rate()

Quoting Alexandra Diupina (2024-09-17 06:22:01)
> get_div() may return zero, so it is necessary to check
> before calling DIV_ROUND_UP_ULL().
> 
> Return value of get_div() depends on reg1, reg2, shift1, shift2
> fields of clk_double_div structure which are filled using the
> PERIPH_DOUBLEDIV macro. This macro is called from the
> PERIPH_CLK_FULL_DD and PERIPH_CLK_MUX_DD macros (the last 4 arguments).
> 
> It is not known exactly what values can be contained in the registers
> at the addresses DIV_SEL0, DIV_SEL1, DIV_SEL2, so the final value of
> div can be zero. Print an error message and return 0 in this case.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 8ca4746a78ab ("clk: mvebu: Add the peripheral clock driver for Armada 3700")
> Signed-off-by: Alexandra Diupina <adiupina@...ralinux.ru>
> ---
> v3: fix indentation
> v2: added explanations to the commit message and printing 
> of an error message when div==0

Please stop sending as replies to previous patches.

>  drivers/clk/mvebu/armada-37xx-periph.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/mvebu/armada-37xx-periph.c b/drivers/clk/mvebu/armada-37xx-periph.c
> index 8701a58a5804..b32c6d4d7ee5 100644
> --- a/drivers/clk/mvebu/armada-37xx-periph.c
> +++ b/drivers/clk/mvebu/armada-37xx-periph.c
> @@ -343,7 +343,12 @@ static unsigned long clk_double_div_recalc_rate(struct clk_hw *hw,
>         div = get_div(double_div->reg1, double_div->shift1);
>         div *= get_div(double_div->reg2, double_div->shift2);
>  
> -       return DIV_ROUND_UP_ULL((u64)parent_rate, div);
> +       if (!div) {
> +               pr_err("Can't recalculate the rate of clock %s\n", hw->init->name);

hw->init is set to NULL after registration (see clk_register() code). If
div is 0 what does the hardware do?

> +               return 0;
> +       } else {
> +               return DIV_ROUND_UP_ULL((u64)parent_rate, div);
> +       }
>  }
>