KVM: s390: pci: fix GAIT table indexing due to double-scaling pointer arithmetic

commit 16d990a upstream.

kvm_s390_pci_aif_enable(), kvm_s390_pci_aif_disable(), and
aen_host_forward() index the GAIT by manually multiplying the index
with sizeof(struct zpci_gaite).

Since aift->gait is already a struct zpci_gaite pointer, this
double-scales the offset, accessing element aisb*16 instead of aisb.

This causes out-of-bounds accesses when aisb >= 32 (with
ZPCI_NR_DEVICES=512)

Fix by removing the erroneous sizeof multiplication.

Fixes: 3c5a1b6 ("KVM: s390: pci: provide routines for enabling/disabling interrupt forwarding")
Fixes: 73f91b0 ("KVM: s390: pci: enable host forwarding of Adapter Event Notifications")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: avasummer

arch/s390/kvm/interrupt.c

@@ -3329,8 +3329,7 @@ static void aen_host_forward(unsigned long si)
 	struct zpci_gaite *gaite;
 	struct kvm *kvm;
 
-	gaite = (struct zpci_gaite *)aift->gait +
-		(si * sizeof(struct zpci_gaite));
+	gaite = aift->gait + si;
 	if (gaite->count == 0)
 		return;
 	if (gaite->aisb != 0)

arch/s390/kvm/pci.c

@@ -292,8 +292,7 @@ static int kvm_s390_pci_aif_enable(struct zpci_dev *zdev, struct zpci_fib *fib,
 				    phys_to_virt(fib->fmt0.aibv));
 
 	spin_lock_irq(&aift->gait_lock);
-	gaite = (struct zpci_gaite *)aift->gait + (zdev->aisb *
-						   sizeof(struct zpci_gaite));
+	gaite = aift->gait + zdev->aisb;
 
 	/* If assist not requested, host will get all alerts */
 	if (assist)
@@ -359,8 +358,7 @@ static int kvm_s390_pci_aif_disable(struct zpci_dev *zdev, bool force)
 	if (zdev->kzdev->fib.fmt0.aibv == 0)
 		goto out;
 	spin_lock_irq(&aift->gait_lock);
-	gaite = (struct zpci_gaite *)aift->gait + (zdev->aisb *
-						   sizeof(struct zpci_gaite));
+	gaite = aift->gait + zdev->aisb;
 	isc = gaite->gisc;
 	gaite->count--;
 	if (gaite->count == 0) {