hv: fix possible null pointer dereference

This patch fix potential null pointer dereference

1, will access null pointer if 'context' is null.
2, if entry already been added to the VM when add
   intx entry for this vm, but parameter virt_pin
   is not equal to entry->virt_sid.intx_id.pin. So
   will saves this entry address to
   vpin_to_pt_entry[entry->virt_sid.intx_id.pin] and
   vpin_to_pt_entry[virt_pin]. In this case, this entry
   will be freed twice.

Tracked-On: #3217
Signed-off-by: Tianhua Sun <tianhuax.s.sun@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/arch/x86/guest/assign.c

@@ -358,6 +358,7 @@ static struct ptirq_remapping_info *add_intx_remapping(struct acrn_vm *vm, uint3
 		uint32_t phys_pin, bool pic_pin)
 {
 	struct ptirq_remapping_info *entry = NULL;
+	bool entry_is_updated = true;
 	uint32_t vpin_src = pic_pin ? PTDEV_VPIN_PIC : PTDEV_VPIN_IOAPIC;
 	DEFINE_IOAPIC_SID(phys_sid, phys_pin, 0U);
 	DEFINE_IOAPIC_SID(virt_sid, virt_pin, vpin_src);
@@ -398,9 +399,10 @@ static struct ptirq_remapping_info *add_intx_remapping(struct acrn_vm *vm, uint3
 		} else {
 			/* The mapping has already been added to the VM. No action
 			 * required. */
+			entry_is_updated = false;
 		}
 
-		if (entry != NULL) {
+		if (entry != NULL && entry_is_updated) {
 			if (pic_pin) {
 				vm->arch_vm.vpic.vpin_to_pt_entry[virt_pin] = entry;
 			} else {

hypervisor/arch/x86/vtd.c

@@ -1182,7 +1182,7 @@ static int32_t remove_iommu_device(const struct iommu_domain *domain, uint16_t s
 
 			context_entry = context + devfun;
 
-			if (context_entry == NULL) {
+			if (context == NULL || context_entry == NULL) {
 				pr_err("dmar context entry is invalid");
 				ret = -EINVAL;
 			} else if ((uint16_t)dmar_get_bitslice(context_entry->hi_64, CTX_ENTRY_UPPER_DID_MASK, CTX_ENTRY_UPPER_DID_POS) != vmid_to_domainid(domain->vm_id)) {