scsi: ibmvfc: Store vhost pointer during subcrq allocation

Currently the back pointer from a queue to the vhost adapter isn't set
until after subcrq interrupt registration. The value is available when a
queue is first allocated and can/should be also set for primary and async
queues as well as subcrqs.

This fixes a crash observed during kexec/kdump on Power 9 with legacy XICS
interrupt controller where a pending subcrq interrupt from the previous
kernel can be replayed immediately upon IRQ registration resulting in
dereference of a garbage backpointer in ibmvfc_interrupt_scsi().

Kernel attempted to read user page (58) - exploit attempt? (uid: 0)
BUG: Kernel NULL pointer dereference on read at 0x00000058
Faulting instruction address: 0xc008000003216a08
Oops: Kernel access of bad area, sig: 11 [#1]
...
NIP [c008000003216a08] ibmvfc_interrupt_scsi+0x40/0xb0 [ibmvfc]
LR [c0000000082079e8] __handle_irq_event_percpu+0x98/0x270
Call Trace:
[c000000047fa3d80] [c0000000123e6180] 0xc0000000123e6180 (unreliable)
[c000000047fa3df0] [c0000000082079e8] __handle_irq_event_percpu+0x98/0x270
[c000000047fa3ea0] [c000000008207d18] handle_irq_event+0x98/0x188
[c000000047fa3ef0] [c00000000820f564] handle_fasteoi_irq+0xc4/0x310
[c000000047fa3f40] [c000000008205c60] generic_handle_irq+0x50/0x80
[c000000047fa3f60] [c000000008015c40] __do_irq+0x70/0x1a0
[c000000047fa3f90] [c000000008016d7c] __do_IRQ+0x9c/0x130
[c000000014622f60] [0000000020000000] 0x20000000
[c000000014622ff0] [c000000008016e50] do_IRQ+0x40/0xa0
[c000000014623020] [c000000008017044] replay_soft_interrupts+0x194/0x2f0
[c000000014623210] [c0000000080172a8] arch_local_irq_restore+0x108/0x170
[c000000014623240] [c000000008eb1008] _raw_spin_unlock_irqrestore+0x58/0xb0
[c000000014623270] [c00000000820b12c] __setup_irq+0x49c/0x9f0
[c000000014623310] [c00000000820b7c0] request_threaded_irq+0x140/0x230
[c000000014623380] [c008000003212a50] ibmvfc_register_scsi_channel+0x1e8/0x2f0 [ibmvfc]
[c000000014623450] [c008000003213d1c] ibmvfc_init_sub_crqs+0xc4/0x1f0 [ibmvfc]
[c0000000146234d0] [c0080000032145a8] ibmvfc_reset_crq+0x150/0x210 [ibmvfc]
[c000000014623550] [c0080000032147c8] ibmvfc_init_crq+0x160/0x280 [ibmvfc]
[c0000000146235f0] [c00800000321a9cc] ibmvfc_probe+0x2a4/0x530 [ibmvfc]

Link: https://lore.kernel.org/r/20220616191126.1281259-2-tyreld@linux.ibm.com
Fixes: 3034ebe ("scsi: ibmvfc: Add alloc/dealloc routines for SCSI Sub-CRQ Channels")
Cc: stable@vger.kernel.org
Reviewed-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ibmvscsi/ibmvfc.c

@@ -5682,6 +5682,8 @@ static int ibmvfc_alloc_queue(struct ibmvfc_host *vhost,
 	queue->cur = 0;
 	queue->fmt = fmt;
 	queue->size = PAGE_SIZE / fmt_size;
+
+	queue->vhost = vhost;
 	return 0;
 }
 
@@ -5787,7 +5789,6 @@ static int ibmvfc_register_scsi_channel(struct ibmvfc_host *vhost,
 	}
 
 	scrq->hwq_id = index;
-	scrq->vhost = vhost;
 
 	LEAVE;
 	return 0;

drivers/scsi/ibmvscsi/ibmvfc.h

@@ -789,6 +789,7 @@ struct ibmvfc_queue {
 	spinlock_t _lock;
 	spinlock_t *q_lock;
 
+	struct ibmvfc_host *vhost;
 	struct ibmvfc_event_pool evt_pool;
 	struct list_head sent;
 	struct list_head free;
@@ -797,7 +798,6 @@ struct ibmvfc_queue {
 	union ibmvfc_iu cancel_rsp;
 
 	/* Sub-CRQ fields */
-	struct ibmvfc_host *vhost;
 	unsigned long cookie;
 	unsigned long vios_cookie;
 	unsigned long hw_irq;