scsi: isci: initialize shost fully before calling scsi_add_host()

scsi_mq_setup_tags(), which is called by scsi_add_host(), calculates the
command size to allocate based on the prot_capabilities. In the isci
driver, scsi_host_set_prot() is called after scsi_add_host() so the command
size gets calculated to be smaller than it needs to be. Eventually,
scsi_mq_init_request() locates the 'prot_sdb' after the command assuming it
was sized correctly and a buffer overrun may occur.

However, seeing blk_mq_alloc_rqs() rounds up to the nearest cache line
size, the mistake can go unnoticed.

The bug was noticed after the struct request size was reduced by commit
9d037ad707ed ("block: remove req->timeout_list")

Which likely reduced the allocated space for the request by an entire cache
line, enough that the overflow could be hit and it caused a panic, on boot,
at:

RIP: 0010:t10_pi_complete+0x77/0x1c0
Call Trace:
<IRQ>
sd_done+0xf5/0x340
scsi_finish_command+0xc3/0x120
blk_done_softirq+0x83/0xb0
__do_softirq+0xa1/0x2e6
irq_exit+0xbc/0xd0
call_function_single_interrupt+0xf/0x20
</IRQ>

sd_done() would call scsi_prot_sg_count() which reads the number of
entities in 'prot_sdb', but seeing 'prot_sdb' is located after the end of
the allocated space it reads a garbage number and erroneously calls
t10_pi_complete().

To prevent this, the calls to scsi_host_set_prot() are moved into
isci_host_alloc() before the call to scsi_add_host(). Out of caution, also
move the similar call to scsi_host_set_guard().

Fixes: 3d2d75254915 ("[SCSI] isci: T10 DIF support")
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Logan Gunthorpe <[e-mail]>
Cc: Intel SCU Linux support <[e-mail]>
Cc: Artur Paszkiewicz <[e-mail]>
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: "Martin K. Petersen" <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Jeff Moyer <[e-mail]>
Reviewed-by: Jeff Moyer <[e-mail]>
Reviewed-by: Jens Axboe <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/isci/init.c

···
 	shost->max_lun = ~0;
 	shost->max_cmd_len = MAX_COMMAND_SIZE;
 
+	/* turn on DIF support */
+	scsi_host_set_prot(shost,
+			   SHOST_DIF_TYPE1_PROTECTION |
+			   SHOST_DIF_TYPE2_PROTECTION |
+			   SHOST_DIF_TYPE3_PROTECTION);
+	scsi_host_set_guard(shost, SHOST_DIX_GUARD_CRC);
+
 	err = scsi_add_host(shost, &pdev->dev);
 	if (err)
 		goto err_shost;
···
 			goto err_host_alloc;
 		}
 		pci_info->hosts[i] = h;
-
-		/* turn on DIF support */
-		scsi_host_set_prot(to_shost(h),
-				   SHOST_DIF_TYPE1_PROTECTION |
-				   SHOST_DIF_TYPE2_PROTECTION |
-				   SHOST_DIF_TYPE3_PROTECTION);
-		scsi_host_set_guard(to_shost(h), SHOST_DIX_GUARD_CRC);
 	}
 
 	err = isci_setup_interrupts(pdev);