linux-kernel - Re: [PATCH][next] nvmem: core: Fix unintentional sign extension issue

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Message-ID: <e0c2b730-7ec2-590d-975c-f515c5b48e2e@linaro.org>
Date:   Thu, 11 Mar 2021 17:50:35 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Colin King <colin.king@...onical.com>,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org
Subject: Re: [PATCH][next] nvmem: core: Fix unintentional sign extension issue



On 11/03/2021 09:53, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The shifting of the u8 integer buf[3] by 24 bits to the left will
> be promoted to a 32 bit signed int and then sign-extended to a
> u64. In the event that the top bit of buf[3] is set then all
> then all the upper 32 bits of the u64 end up as also being set
> because of the sign-extension. Fix this by casting buf[i] to
> a u64 before the shift.
> 
> Addresses-Coverity: ("Unintended sign extension")
> Fixes: 097eb1136ebb ("nvmem: core: Add functions to make number reading easy")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---

Applied thanks,

--srini

>   drivers/nvmem/core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 635e3131eb5f..bca671ff4e54 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -1693,7 +1693,7 @@ int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id,
>   	/* Copy w/ implicit endian conversion */
>   	*val = 0;
>   	for (i = 0; i < len; i++)
> -		*val |= buf[i] << (8 * i);
> +		*val |= (uint64_t)buf[i] << (8 * i);
>   
>   	kfree(buf);
>   
>