RE: [PATCH] stm class: Fix out of bound access from bitmap allocation

[David Laight <David.Laight@ACULAB.COM>]

From: Sai Prakash Ranjan
> Sent: 05 April 2019 13:23
> 
> From: Mulu He <muluhe@codeaurora.org>
> 
> Bitmap allocation works on array of unsigned longs and
> for stm master allocation when the number of software
> channels is 32, 4 bytes are allocated and there is a out of
> bound access at the first 8 bytes access of bitmap region.
> 
> Fixes: 7bd1d4093c2f ("stm class: Introduce an abstraction for System Trace Module devices")
> Signed-off-by: Mulu He <muluhe@codeaurora.org>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> Cc: stable@vger.kernel.org
> ---
>  drivers/hwtracing/stm/core.c | 2 +-
>  drivers/hwtracing/stm/stm.h  | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> index 93ce3aa740a9..21a5838f6e67 100644
> --- a/drivers/hwtracing/stm/core.c
> +++ b/drivers/hwtracing/stm/core.c
> @@ -168,7 +168,7 @@ static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
>  	struct stp_master *master;
>  	size_t size;
> 
> -	size = ALIGN(stm->data->sw_nchannels, 8) / 8;
> +	size = ALIGN(stm->data->sw_nchannels, STM_MASTER_SZ) / STM_MASTER_SZ;

I'm not sure that using STP_MASTER_SZ improves readability at all.

Is there something that gives the size of a bitmap for 'n' items?

	David

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