scsi: mvumi: Replace 1-element arrays with flexible array members

One-element arrays (and multi-element arrays being treated as dynamically
sized) are deprecated[1] and are being replaced with flexible array members
in support of the ongoing efforts to tighten the FORTIFY_SOURCE routines on
memcpy(), correctly instrument array indexing with UBSAN_BOUNDS, and to
globally enable -fstrict-flex-arrays=3.

Replace one-element arrays with flexible-array member in struct
mvumi_msg_frame, struct mvumi_rsp_frame, and struct mvumi_hs_header,
adjusting the explicit sizing calculations at the same time.

This results in no functional differences in binary output. An explicit add
is now folded into the size calculation:

│       mov    0x1070(%r14),%eax
│ -     add    $0x4,%eax
│ -     movabs $0xfffffffdc,%rbx
│ +     movabs $0xfffffffe0,%rbx
│       add    %rax,%rbx

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays

Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230105011143.never.569-kees@kernel.orgSigned-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mvumi.c

@@ -1841,7 +1841,7 @@ static enum mvumi_qc_result mvumi_send_command(struct mvumi_hba *mhba,
 	cmd->frame->request_id = mhba->io_seq++;
 	cmd->request_id = cmd->frame->request_id;
 	mhba->tag_cmd[cmd->frame->tag] = cmd;
-	frame_len = sizeof(*ib_frame) - 4 +
+	frame_len = sizeof(*ib_frame) +
 				ib_frame->sg_counts * sizeof(struct mvumi_sgl);
 	if (mhba->hba_capability & HS_CAPABILITY_SUPPORT_DYN_SRC) {
 		struct mvumi_dyn_list_entry *dle;
@@ -2387,7 +2387,7 @@ static int mvumi_io_attach(struct mvumi_hba *mhba)
 	struct Scsi_Host *host = mhba->shost;
 	struct scsi_device *sdev = NULL;
 	int ret;
-	unsigned int max_sg = (mhba->ib_max_size + 4 -
+	unsigned int max_sg = (mhba->ib_max_size -
 		sizeof(struct mvumi_msg_frame)) / sizeof(struct mvumi_sgl);
 
 	host->irq = mhba->pdev->irq;

drivers/scsi/mvumi.h

@@ -279,7 +279,7 @@ struct mvumi_msg_frame {
 	u16 request_id;
 	u16 reserved1;
 	u8 cdb[MAX_COMMAND_SIZE];
-	u32 payload[1];
+	u32 payload[];
 };
 
 /*
@@ -294,7 +294,7 @@ struct mvumi_rsp_frame {
 	u8 req_status;
 	u8 rsp_flag;	/* Indicates the type of Data_Payload.*/
 	u16 request_id;
-	u32 payload[1];
+	u32 payload[];
 };
 
 struct mvumi_ob_data {
@@ -380,7 +380,7 @@ struct mvumi_hs_header {
 	u8	page_code;
 	u8	checksum;
 	u16	frame_length;
-	u32	frame_content[1];
+	u32	frame_content[];
 };
 
 /*