diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index ef14b00fa94b..135ae5222cf3 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -1331,8 +1331,8 @@ static int __init init_iommu_from_acpi(struct amd_iommu *iommu,
 		}
 		case IVHD_DEV_ACPI_HID: {
 			u16 devid;
-			u8 hid[ACPIHID_HID_LEN] = {0};
-			u8 uid[ACPIHID_UID_LEN] = {0};
+			u8 hid[ACPIHID_HID_LEN];
+			u8 uid[ACPIHID_UID_LEN];
 			int ret;
 
 			if (h->type != 0x40) {
@@ -1349,6 +1349,7 @@ static int __init init_iommu_from_acpi(struct amd_iommu *iommu,
 				break;
 			}
 
+			uid[0] = '\0';
 			switch (e->uidf) {
 			case UID_NOT_PRESENT:
 
@@ -1363,8 +1364,8 @@ static int __init init_iommu_from_acpi(struct amd_iommu *iommu,
 				break;
 			case UID_IS_CHARACTER:
 
-				memcpy(uid, (u8 *)(&e->uid), ACPIHID_UID_LEN - 1);
-				uid[ACPIHID_UID_LEN - 1] = '\0';
+				memcpy(uid, &e->uid, e->uidl);
+				uid[e->uidl] = '\0';
 
 				break;
 			default: