KVM: arm64: vgic: Add more checks when restoring ITS tables

Try to improve the predictability of ITS save/restores (and debuggability
of failed ITS saves) by failing early on restore when trying to read
corrupted tables.

Restoring the ITS tables does some checks for corrupted tables, but not as
many as in a save: an overflowing device ID will be detected on save but
not on restore.  The consequence is that restoring a corrupted table won't
be detected until the next save; including the ITS not working as expected
after the restore.  As an example, if the guest sets tables overlapping
each other, which would most likely result in some corrupted table, this is
what we would see from the host point of view:

	guest sets base addresses that overlap each other
	save ioctl
	restore ioctl
	save ioctl (fails)

Ideally, we would like the first save to fail, but overlapping tables could
actually be intended by the guest. So, let's at least fail on the restore
with some checks: like checking that device and event IDs don't overflow
their tables.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220510001633.552496-3-ricarkol@google.com

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index 93a5178374c9..8a7db839e3bf 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -2198,6 +2198,9 @@ static int vgic_its_restore_ite(struct vgic_its *its, u32 event_id,
 	if (!collection)
 		return -EINVAL;
 
+	if (!vgic_its_check_event_id(its, dev, event_id))
+		return -EINVAL;
+
 	ite = vgic_its_alloc_ite(dev, collection, event_id);
 	if (IS_ERR(ite))
 		return PTR_ERR(ite);
@@ -2319,6 +2322,7 @@ static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
 				void *ptr, void *opaque)
 {
 	struct its_device *dev;
+	u64 baser = its->baser_device_table;
 	gpa_t itt_addr;
 	u8 num_eventid_bits;
 	u64 entry = *(u64 *)ptr;
@@ -2339,6 +2343,9 @@ static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
 	/* dte entry is valid */
 	offset = (entry & KVM_ITS_DTE_NEXT_MASK) >> KVM_ITS_DTE_NEXT_SHIFT;
 
+	if (!vgic_its_check_id(its, baser, id, NULL))
+		return -EINVAL;
+
 	dev = vgic_its_alloc_device(its, id, itt_addr, num_eventid_bits);
 	if (IS_ERR(dev))
 		return PTR_ERR(dev);