ath10k: prevent using invalid ringbuffer indexes

If the device is removed and hotplug fails
ioread32() will return 0xFFFFFFFF. In that case
reading ringbuffer during device bringup led to
out-of-bounds addressing of a ringbuffer array
that in turn led to a paging failure.

This could be reproduced by the following:
 * boot without acpi/prevent hotplug from working
 * insert and manually detect (pci rescan) the device
 * remove the device physically
 * load ath10k driver
 * kernel crashed

Ringbuffer index reading is now protected by using
an appropriate mask to prevent addressing an
invalid array index.
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/ce.c

@@ -637,6 +637,7 @@ static int ath10k_ce_completed_send_next_nolock(struct ce_state *ce_state,
 		ath10k_pci_wake(ar);
 		src_ring->hw_index =
 			ath10k_ce_src_ring_read_index_get(ar, ctrl_addr);
+		src_ring->hw_index &= nentries_mask;
 		ath10k_pci_sleep(ar);
 	}
 	read_index = src_ring->hw_index;
@@ -950,10 +951,12 @@ static int ath10k_ce_init_src_ring(struct ath10k *ar,
 
 	ath10k_pci_wake(ar);
 	src_ring->sw_index = ath10k_ce_src_ring_read_index_get(ar, ctrl_addr);
+	src_ring->sw_index &= src_ring->nentries_mask;
 	src_ring->hw_index = src_ring->sw_index;
 
 	src_ring->write_index =
 		ath10k_ce_src_ring_write_index_get(ar, ctrl_addr);
+	src_ring->write_index &= src_ring->nentries_mask;
 	ath10k_pci_sleep(ar);
 
 	src_ring->per_transfer_context = (void **)ptr;
@@ -1035,8 +1038,10 @@ static int ath10k_ce_init_dest_ring(struct ath10k *ar,
 
 	ath10k_pci_wake(ar);
 	dest_ring->sw_index = ath10k_ce_dest_ring_read_index_get(ar, ctrl_addr);
+	dest_ring->sw_index &= dest_ring->nentries_mask;
 	dest_ring->write_index =
 		ath10k_ce_dest_ring_write_index_get(ar, ctrl_addr);
+	dest_ring->write_index &= dest_ring->nentries_mask;
 	ath10k_pci_sleep(ar);
 
 	dest_ring->per_transfer_context = (void **)ptr;