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

[Seth Heasley]

On Tue, 2022-04-05 at 17:15 +0200, Borislav Petkov wrote:
> From: Borislav Petkov <bp@xxxxxxx>
> 
> 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@xxxxxxx for the gory
> details as to why it triggers with older gccs only.
> 
> Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Seth Heasley <seth.heasley@xxxxxxxxx>

> Cc: Seth Heasley <seth.heasley@xxxxxxxxx>
> Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
> Cc: Wolfram Sang <wsa@xxxxxxxxxx>
> Cc: linux-i2c@xxxxxxxxxxxxxxx
> ---
>  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 */