linux-hardening - Re: [PATCH] bus: mhi: core: Use correctly sized arguments for bit field

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Date:   Thu, 16 Dec 2021 10:55:45 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Hemant Kumar <hemantk@...eaurora.org>,
        Bhaumik Bhatt <quic_bbhatt@...cinc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Loic Poulain <loic.poulain@...aro.org>,
        Yury Norov <yury.norov@...il.com>,
        Carl Huang <cjhuang@...eaurora.org>,
        Carl Yin <carl.yin@...ctel.com>, linux-kernel@...r.kernel.org,
        mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] bus: mhi: core: Use correctly sized arguments for bit
 field

On Wed, Dec 15, 2021 at 03:24:46PM -0800, Kees Cook wrote:
> The find.h APIs are designed to be used only on unsigned long arguments.
> This can technically result in a over-read, but it is harmless in this
> case. Regardless, fix it to avoid the warning seen under -Warray-bounds,
> which we'd like to enable globally:
> 
> In file included from ./include/linux/bitmap.h:9,
>                  from ./include/linux/cpumask.h:12,
>                  from ./arch/x86/include/asm/cpumask.h:5,
>                  from ./arch/x86/include/asm/msr.h:11,
>                  from ./arch/x86/include/asm/processor.h:22,
>                  from ./arch/x86/include/asm/cpufeature.h:5,
>                  from ./arch/x86/include/asm/thread_info.h:53,
>                  from ./include/linux/thread_info.h:60,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/spinlock.h:55,
>                  from ./include/linux/wait.h:9,
>                  from ./include/linux/wait_bit.h:8,
>                  from ./include/linux/fs.h:6,
>                  from ./include/linux/debugfs.h:15,
>                  from drivers/bus/mhi/core/init.c:7:
> drivers/bus/mhi/core/init.c: In function 'to_mhi_pm_state_str':
> ./include/linux/find.h:187:37: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'enum mhi_pm_state[1]' [-Warray-bounds]
>   187 |                 unsigned long val = *addr & GENMASK(size - 1, 0);
>       |                                     ^~~~~
> drivers/bus/mhi/core/init.c:80:51: note: while referencing 'state'
>    80 | const char *to_mhi_pm_state_str(enum mhi_pm_state state)
>       |                                 ~~~~~~~~~~~~~~~~~~^~~~~
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Manivannan Sadhasivam <mani@...nel.org>

A small nit pick below but I'll fix it up while applying.

Thanks,
Mani

> ---
>  drivers/bus/mhi/core/init.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
> index f1ec34417592..b91f75fff962 100644
> --- a/drivers/bus/mhi/core/init.c
> +++ b/drivers/bus/mhi/core/init.c
> @@ -79,7 +79,8 @@ static const char * const mhi_pm_state_str[] = {
>  
>  const char *to_mhi_pm_state_str(enum mhi_pm_state state)
>  {
> -	int index = find_last_bit((unsigned long *)&state, 32);
> +	unsigned long bits = state;

Variable "bits" could be changed to "pm_state".

> +	int index = find_last_bit(&bits, 32);
>  
>  	if (index >= ARRAY_SIZE(mhi_pm_state_str))
>  		return "Invalid State";
> -- 
> 2.30.2
>