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From:   Kalle Valo <kvalo@kernel.org>
To:     Ping-Ke Shih <pkshih@realtek.com>
Cc:     <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH] wifi: rtw89: use FIELD_PREP to fill MAC quota value
References: <20221103072420.15161-1-pkshih@realtek.com>
Date:   Mon, 07 Nov 2022 14:28:47 +0200
In-Reply-To: <20221103072420.15161-1-pkshih@realtek.com> (Ping-Ke Shih's
        message of "Thu, 3 Nov 2022 15:24:20 +0800")
Message-ID: <87zgd3t0cg.fsf@kernel.org>
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Ping-Ke Shih <pkshih@realtek.com> writes:

> Coverity reported shift 16 bits could cause sign extension and might get
> an unexpected value. Since the input values are predefined and no this
> kind of case, original code is safe so far. But, still changing them to
> use FIELD_PREP() will be more clear and prevent mistakes in the future.
>
> The original message of Coverity is:
>   Suspicious implicit sign extension: "max_cfg->cma0_dma" with type "u16"
>   (16 bits, unsigned) is promoted in "max_cfg->cma0_dma << 16" to type
>   "int" (32 bits, signed), then sign-extended to type "unsigned long"
>   (64 bits, unsigned).  If "max_cfg->cma0_dma << 16" is greater than
>   0x7FFFFFFF, the upper bits of the result will all be 1."
>
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1527095 ("Integer handling issues")
> Fixes: e3ec7017f6a2 ("rtw89: add Realtek 802.11ax driver")
> Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
> ---
>  drivers/net/wireless/realtek/rtw89/mac.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/wireless/realtek/rtw89/mac.c b/drivers/net/wireless/realtek/rtw89/mac.c
> index bb49033b587d2..11081dfdfb172 100644
> --- a/drivers/net/wireless/realtek/rtw89/mac.c
> +++ b/drivers/net/wireless/realtek/rtw89/mac.c
> @@ -1487,10 +1487,8 @@ static int dle_mix_cfg(struct rtw89_dev *rtwdev, const struct rtw89_dle_mem *cfg
>  #define INVALID_QT_WCPU U16_MAX
>  #define SET_QUOTA_VAL(_min_x, _max_x, _module, _idx)			\
>  	do {								\
> -		val = ((_min_x) &					\
> -		       B_AX_ ## _module ## _MIN_SIZE_MASK) |		\
> -		      (((_max_x) << 16) &				\
> -		       B_AX_ ## _module ## _MAX_SIZE_MASK);		\
> +		val = FIELD_PREP(B_AX_ ## _module ## _MIN_SIZE_MASK, _min_x) | \
> +		      FIELD_PREP(B_AX_ ## _module ## _MAX_SIZE_MASK, _max_x);  \

BTW in wireless nowadays the preference is to use u32_encode_bits() & co
instead of FIELD_PREP(). Not an issue for this patch, just wanted to
mention anyway.

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