scsi: lpfc: Use struct_group to isolate cast to larger object

When building under -Warray-bounds, a warning is generated when casting a
u32 into MAILBOX_t (which is larger). This warning is conservative, but
it's not an unreasonable change to make to improve future robustness. Use a
tagged struct_group that can refer to either the specific fields or the
first u32 separately, silencing this warning:

drivers/scsi/lpfc/lpfc_sli.c: In function 'lpfc_reset_barrier':
drivers/scsi/lpfc/lpfc_sli.c:4787:29: error: array subscript 'MAILBOX_t[0]' is partly outside array bounds of 'volatile uint32_t[1]' {aka 'volatile unsigned int[1]'} [-Werror=array-bounds]
 4787 |         ((MAILBOX_t *)&mbox)->mbxCommand = MBX_KILL_BOARD;
      |                             ^~
drivers/scsi/lpfc/lpfc_sli.c:4752:27: note: while referencing 'mbox'
 4752 |         volatile uint32_t mbox;
      |                           ^~~~

There is no change to the resulting executable instruction code.

Link: https://lore.kernel.org/r/20211203223351.107323-1-keescook@chromium.org
Reviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 17 insertions, 10 deletions

diff --git a/drivers/scsi/lpfc/lpfc_hw.h b/drivers/scsi/lpfc/lpfc_hw.h
index 61c9db31d9da..4461c3d6fc4f 100644
--- a/drivers/scsi/lpfc/lpfc_hw.h
+++ b/drivers/scsi/lpfc/lpfc_hw.h
@@ -3675,19 +3675,26 @@ union sli_var {
 };
 
 typedef struct {
+	struct_group_tagged(MAILBOX_word0, bits,
+		union {
+			struct {
 #ifdef __BIG_ENDIAN_BITFIELD
-	uint16_t mbxStatus;
-	uint8_t mbxCommand;
-	uint8_t mbxReserved:6;
-	uint8_t mbxHc:1;
-	uint8_t mbxOwner:1;	/* Low order bit first word */
+				uint16_t mbxStatus;
+				uint8_t mbxCommand;
+				uint8_t mbxReserved:6;
+				uint8_t mbxHc:1;
+				uint8_t mbxOwner:1;	/* Low order bit first word */
 #else	/*  __LITTLE_ENDIAN_BITFIELD */
-	uint8_t mbxOwner:1;	/* Low order bit first word */
-	uint8_t mbxHc:1;
-	uint8_t mbxReserved:6;
-	uint8_t mbxCommand;
-	uint16_t mbxStatus;
+				uint8_t mbxOwner:1;	/* Low order bit first word */
+				uint8_t mbxHc:1;
+				uint8_t mbxReserved:6;
+				uint8_t mbxCommand;
+				uint16_t mbxStatus;
 #endif
+			};
+			u32 word0;
+		};
+	);
 
 	MAILVARIANTS un;
 	union sli_var us;