linux-kernel - Re: [PATCH 05/11] i2c: ismt: Fix undefined behavior due to shift overflowing the constant

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Date:   Tue, 05 Apr 2022 14:18:21 -0700
From:   Seth Heasley <seth.heasley@...el.com>
To:     Borislav Petkov <bp@...en8.de>, LKML <linux-kernel@...r.kernel.org>
Cc:     Neil Horman <nhorman@...driver.com>, Wolfram Sang <wsa@...nel.org>,
        linux-i2c@...r.kernel.org, seth.heasley@...el.com
Subject: Re: [PATCH 05/11] i2c: ismt: Fix undefined behavior due to shift
 overflowing the constant

On Tue, 2022-04-05 at 17:15 +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Fix:
> 
>   drivers/i2c/busses/i2c-ismt.c: In function ‘ismt_hw_init’:
>   drivers/i2c/busses/i2c-ismt.c:770:2: error: case label does not
> reduce to an integer constant
>     case ISMT_SPGT_SPD_400K:
>     ^~~~
>   drivers/i2c/busses/i2c-ismt.c:773:2: error: case label does not
> reduce to an integer constant
>     case ISMT_SPGT_SPD_1M:
>     ^~~~
> 
> See https://lore.kernel.org/r/YkwQ6%2BtIH8GQpuct@zn.tnic for the gory
> details as to why it triggers with older gccs only.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Seth Heasley <seth.heasley@...el.com>

> Cc: Seth Heasley <seth.heasley@...el.com>
> Cc: Neil Horman <nhorman@...driver.com>
> Cc: Wolfram Sang <wsa@...nel.org>
> Cc: linux-i2c@...r.kernel.org
> ---
>  drivers/i2c/busses/i2c-ismt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-ismt.c b/drivers/i2c/busses/i2c-
> ismt.c
> index f4820fd3dc13..c0364314877e 100644
> --- a/drivers/i2c/busses/i2c-ismt.c
> +++ b/drivers/i2c/busses/i2c-ismt.c
> @@ -145,8 +145,8 @@
>  #define ISMT_SPGT_SPD_MASK	0xc0000000	/* SMBus Speed mask
> */
>  #define ISMT_SPGT_SPD_80K	0x00		/* 80 kHz */
>  #define ISMT_SPGT_SPD_100K	(0x1 << 30)	/* 100 kHz */
> -#define ISMT_SPGT_SPD_400K	(0x2 << 30)	/* 400 kHz */
> -#define ISMT_SPGT_SPD_1M	(0x3 << 30)	/* 1 MHz */
> +#define ISMT_SPGT_SPD_400K	(0x2U << 30)	/* 400 kHz */
> +#define ISMT_SPGT_SPD_1M	(0x3U << 30)	/* 1 MHz */
>  
>  
>  /* MSI Control Register (MSICTL) bit definitions */