Re: [PATCH v2 1/1] scsi: qla2xxx: replace non-standard flexible array purex_item.iocb

["Gustavo A. R. Silva" <gustavo@embeddedor.com>]

On 28/07/25 12:57, Chris Leech wrote:
> purex_item.iocb is defined as a 64-element u8 array, but 64 is the
> minimum size and it can be allocated larger.
> This makes it a standard empty flex array.
> 
> This was motivated by field-spanning write warnings during FPIN testing.
> https://lore.kernel.org/linux-nvme/20250709211919.49100-1-bgurney@redhat.com/
> 
>    >  kernel: memcpy: detected field-spanning write (size 60) of single field
>    >  "((uint8_t *)fpin_pkt + buffer_copy_offset)"
>    >  at drivers/scsi/qla2xxx/qla_isr.c:1221 (size 44)
> 
> I removed the outer wrapper from the iocb flex array, so that it can be
> linked to purex_item.size with __counted_by.
> 
> The non-flex-array portion of purex_item is now defined within the
> struct_group_tagged macro to create a type definition for just the
> header. This was then used for the scsi_qla_host.default_item
> definition to deal with -Wflex-array-member-not-at-end warnings.
> 
> These changes remove the default minimum 64-byte allocation, requiring
> further changes.
> 
>    In struct scsi_qla_host the embedded default_item is now followed by
>    __default_item_iocb[QLA_DEFAULT_PAYLOAD_SIZE] to reserve space that
>    will be used as default_item.iocb
> 
>    qla24xx_alloc_purex_item is adjusted to no longer expect the default
>    minimum size to be part of sizeof(struct purex_item), the entire
>    flexible array size is added to the structure size for allocation.
> 
> This also slightly changes the layout of the purex_item struct, as
> 2-bytes of padding are added to purex_item_hdr and therefor between size
> and iocb. The resulting size is the same, but iocb is shifted 2-bytes
> (the old purex_item was padded at the end, after the 64-byte defined
> array size). I don't think this is a problem.
> 
> Tested-by: Bryan Gurney <bgurney@redhat.com>
> Signed-off-by: Chris Leech <cleech@redhat.com>
> ---
>   drivers/scsi/qla2xxx/qla_def.h  | 23 ++++++++++++-----------
>   drivers/scsi/qla2xxx/qla_isr.c  | 19 +++++++++----------
>   drivers/scsi/qla2xxx/qla_nvme.c |  2 +-
>   drivers/scsi/qla2xxx/qla_os.c   |  9 +++++----
>   4 files changed, 27 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
> index cb95b7b12051d..0e7d201b1feb0 100644
> --- a/drivers/scsi/qla2xxx/qla_def.h
> +++ b/drivers/scsi/qla2xxx/qla_def.h
> @@ -4883,16 +4883,16 @@ struct active_regions {
>    * is variable) starting at "iocb".
>    */
>   struct purex_item {
> -	void *purls_context;
> -	struct list_head list;
> -	struct scsi_qla_host *vha;
> -	void (*process_item)(struct scsi_qla_host *vha,
> -			     struct purex_item *pkt);
> -	atomic_t in_use;
> -	uint16_t size;
> -	struct {
> -		uint8_t iocb[64];
> -	} iocb;
> +	struct_group_tagged(purex_item_hdr, __hdr,
> +		void *purls_context;
> +		struct list_head list;
> +		struct scsi_qla_host *vha;
> +		void (*process_item)(struct scsi_qla_host *vha,
> +				     struct purex_item *pkt);
> +		atomic_t in_use;
> +		uint16_t size;
> +	);
> +	uint8_t iocb[] __counted_by(size);
>   };
>   
>   #include "qla_edif.h"
> @@ -5101,7 +5101,8 @@ typedef struct scsi_qla_host {
>   		struct list_head head;
>   		spinlock_t lock;
>   	} purex_list;
> -	struct purex_item default_item;
> +	struct purex_item_hdr default_item;
> +	uint8_t __default_item_iocb[QLA_DEFAULT_PAYLOAD_SIZE];
>   
>   	struct name_list_extended gnl;
>   	/* Count of active session/fcport */
> diff --git a/drivers/scsi/qla2xxx/qla_isr.c b/drivers/scsi/qla2xxx/qla_isr.c
> index fe98c76e9be32..a00c06a9898ec 100644
> --- a/drivers/scsi/qla2xxx/qla_isr.c
> +++ b/drivers/scsi/qla2xxx/qla_isr.c
> @@ -1077,17 +1077,17 @@ static struct purex_item *
>   qla24xx_alloc_purex_item(scsi_qla_host_t *vha, uint16_t size)
>   {
>   	struct purex_item *item = NULL;
> -	uint8_t item_hdr_size = sizeof(*item);
>   
>   	if (size > QLA_DEFAULT_PAYLOAD_SIZE) {
> -		item = kzalloc(item_hdr_size +
> -		    (size - QLA_DEFAULT_PAYLOAD_SIZE), GFP_ATOMIC);
> +		item = kzalloc(struct_size(item, iocb, size), GFP_ATOMIC);

With the inclusion of `counted_by`, I think `item->size` should be updated
here:
		item->size = size;

>   	} else {
>   		if (atomic_inc_return(&vha->default_item.in_use) == 1) {
> -			item = &vha->default_item;
> +			item = (struct purex_item *)&vha->default_item;
>   			goto initialize_purex_header;
>   		} else {
> -			item = kzalloc(item_hdr_size, GFP_ATOMIC);
> +			item = kzalloc(
> +				struct_size(item, iocb, QLA_DEFAULT_PAYLOAD_SIZE),
> +				GFP_ATOMIC);

...and here:
			item->size = QLA_DEFAULT_PAYLOAD_SIZE;

Then remove `item->size = size;` just before `return item;`

Thanks
-Gustavo

>   		}
>   	}
>   	if (!item) {
> @@ -1127,17 +1127,16 @@ qla24xx_queue_purex_item(scsi_qla_host_t *vha, struct purex_item *pkt,
>    * @vha: SCSI driver HA context
>    * @pkt: ELS packet
>    */
> -static struct purex_item
> -*qla24xx_copy_std_pkt(struct scsi_qla_host *vha, void *pkt)
> +static struct purex_item *
> +qla24xx_copy_std_pkt(struct scsi_qla_host *vha, void *pkt)
>   {
>   	struct purex_item *item;
>   
> -	item = qla24xx_alloc_purex_item(vha,
> -					QLA_DEFAULT_PAYLOAD_SIZE);
> +	item = qla24xx_alloc_purex_item(vha, QLA_DEFAULT_PAYLOAD_SIZE);
>   	if (!item)
>   		return item;
>   
> -	memcpy(&item->iocb, pkt, sizeof(item->iocb));
> +	memcpy(&item->iocb, pkt, QLA_DEFAULT_PAYLOAD_SIZE);
>   	return item;
>   }
>   
> diff --git a/drivers/scsi/qla2xxx/qla_nvme.c b/drivers/scsi/qla2xxx/qla_nvme.c
> index 8ee2e337c9e1b..92488890bc04e 100644
> --- a/drivers/scsi/qla2xxx/qla_nvme.c
> +++ b/drivers/scsi/qla2xxx/qla_nvme.c
> @@ -1308,7 +1308,7 @@ void qla2xxx_process_purls_iocb(void **pkt, struct rsp_que **rsp)
>   
>   	ql_dbg(ql_dbg_unsol, vha, 0x2121,
>   	       "PURLS OP[%01x] size %d xchg addr 0x%x portid %06x\n",
> -	       item->iocb.iocb[3], item->size, uctx->exchange_address,
> +	       item->iocb[3], item->size, uctx->exchange_address,
>   	       fcport->d_id.b24);
>   	/* +48    0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F
>   	 * ----- -----------------------------------------------
> diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
> index d4b484c0fd9d7..ef8a4fce0e03c 100644
> --- a/drivers/scsi/qla2xxx/qla_os.c
> +++ b/drivers/scsi/qla2xxx/qla_os.c
> @@ -3971,7 +3971,7 @@ qla2x00_remove_one(struct pci_dev *pdev)
>   static inline void
>   qla24xx_free_purex_list(struct purex_list *list)
>   {
> -	struct purex_item *item, *next;
> +	struct purex_item_hdr *item, *next;
>   	ulong flags;
>   
>   	spin_lock_irqsave(&list->lock, flags);
> @@ -6459,9 +6459,10 @@ void qla24xx_process_purex_rdp(struct scsi_qla_host *vha,
>   void
>   qla24xx_free_purex_item(struct purex_item *item)
>   {
> -	if (item == &item->vha->default_item)
> -		memset(&item->vha->default_item, 0, sizeof(struct purex_item));
> -	else
> +	if (item == (struct purex_item *)&item->vha->default_item) {
> +		memset(&item->vha->default_item, 0, sizeof(struct purex_item_hdr));
> +		memset(&item->vha->__default_item_iocb, 0, QLA_DEFAULT_PAYLOAD_SIZE);
> +	} else
>   		kfree(item);
>   }
>