Re: [PATCH] sata_fsl: Use struct_group() for memcpy() region

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 2021/11/19 3:38, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally writing across neighboring fields.
> 
> Use struct_group() in struct command_desc around members acmd and fill,
> so they can be referenced together. This will allow memset(), memcpy(),
> and sizeof() to more easily reason about sizes, improve readability,
> and avoid future warnings about writing beyond the end of acmd:
> 
> In function 'fortify_memset_chk',
>     inlined from 'sata_fsl_qc_prep' at drivers/ata/sata_fsl.c:534:3:
> ./include/linux/fortify-string.h:199:4: warning: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
>   199 |    __write_overflow_field();
>       |    ^~~~~~~~~~~~~~~~~~~~~~~~
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

This lacks some context with regard to FORTIFY_SOURCE and struct_group(). Is
that already in 5.16 ? It sounds like it is not. Do you want a ack ? Or do you
want me to queue this up for 5.17 ?

Cheers.

> ---
>  drivers/ata/sata_fsl.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/ata/sata_fsl.c b/drivers/ata/sata_fsl.c
> index e5838b23c9e0..fec3c9032606 100644
> --- a/drivers/ata/sata_fsl.c
> +++ b/drivers/ata/sata_fsl.c
> @@ -246,8 +246,10 @@ enum {
>  struct command_desc {
>  	u8 cfis[8 * 4];
>  	u8 sfis[8 * 4];
> -	u8 acmd[4 * 4];
> -	u8 fill[4 * 4];
> +	struct_group(cdb,
> +		u8 acmd[4 * 4];
> +		u8 fill[4 * 4];
> +	);
>  	u32 prdt[SATA_FSL_MAX_PRD_DIRECT * 4];
>  	u32 prdt_indirect[(SATA_FSL_MAX_PRD - SATA_FSL_MAX_PRD_DIRECT) * 4];
>  };
> @@ -531,8 +533,8 @@ static enum ata_completion_errors sata_fsl_qc_prep(struct ata_queued_cmd *qc)
>  	/* setup "ACMD - atapi command" in cmd. desc. if this is ATAPI cmd */
>  	if (ata_is_atapi(qc->tf.protocol)) {
>  		desc_info |= ATAPI_CMD;
> -		memset((void *)&cd->acmd, 0, 32);
> -		memcpy((void *)&cd->acmd, qc->cdb, qc->dev->cdb_len);
> +		memset(&cd->cdb, 0, sizeof(cd->cdb));
> +		memcpy(&cd->cdb, qc->cdb, qc->dev->cdb_len);
>  	}
>  
>  	if (qc->flags & ATA_QCFLAG_DMAMAP)
> 


-- 
Damien Le Moal
Western Digital Research