diff --git a/pvmfw/src/virtio/hal.rs b/pvmfw/src/virtio/hal.rs
index c6c7a99..5f70b33 100644
--- a/pvmfw/src/virtio/hal.rs
+++ b/pvmfw/src/virtio/hal.rs
@@ -1,5 +1,9 @@
+use super::pci::PCI_INFO;
 use crate::memory::{alloc_shared, dealloc_shared, phys_to_virt, virt_to_phys};
-use core::ptr::{copy_nonoverlapping, NonNull};
+use core::{
+    ops::Range,
+    ptr::{copy_nonoverlapping, NonNull},
+};
 use log::debug;
 use virtio_drivers::{BufferDirection, Hal, PhysAddr, PAGE_SIZE};
 
@@ -26,7 +30,21 @@
         0
     }
 
-    fn mmio_phys_to_virt(paddr: PhysAddr, _size: usize) -> NonNull<u8> {
+    fn mmio_phys_to_virt(paddr: PhysAddr, size: usize) -> NonNull<u8> {
+        let pci_info = PCI_INFO.get().expect("VirtIO HAL used before PCI_INFO was initialised");
+        // Check that the region is within the PCI MMIO range that we read from the device tree. If
+        // not, the host is probably trying to do something malicious.
+        if !contains_range(
+            &pci_info.bar_range,
+            &(paddr.try_into().expect("PCI MMIO region start was outside of 32-bit address space")
+                ..paddr
+                    .checked_add(size)
+                    .expect("PCI MMIO region end overflowed")
+                    .try_into()
+                    .expect("PCI MMIO region end was outside of 32-bit address space")),
+        ) {
+            panic!("PCI MMIO region was outside of expected BAR range.");
+        }
         phys_to_virt(paddr)
     }
 
@@ -68,3 +86,8 @@
         }
     }
 }
+
+/// Returns true if `inner` is entirely contained within `outer`.
+fn contains_range(outer: &Range<u32>, inner: &Range<u32>) -> bool {
+    inner.start >= outer.start && inner.end <= outer.end
+}
diff --git a/pvmfw/src/virtio/pci.rs b/pvmfw/src/virtio/pci.rs
index f9d36c6..d3b3124 100644
--- a/pvmfw/src/virtio/pci.rs
+++ b/pvmfw/src/virtio/pci.rs
@@ -16,8 +16,10 @@
 
 use super::hal::HalImpl;
 use crate::{entry::RebootReason, memory::MemoryTracker};
+use alloc::boxed::Box;
 use fdtpci::{PciError, PciInfo};
 use log::{debug, error, info};
+use once_cell::race::OnceBox;
 use virtio_drivers::{
     device::blk::VirtIOBlk,
     transport::{
@@ -26,8 +28,29 @@
     },
 };
 
+pub(super) static PCI_INFO: OnceBox<PciInfo> = OnceBox::new();
+
+/// Prepares to use VirtIO PCI devices.
+///
+/// In particular:
+///
+/// 1. Maps the PCI CAM and BAR range in the page table and MMIO guard.
+/// 2. Stores the `PciInfo` for the VirtIO HAL to use later.
+/// 3. Creates and returns a `PciRoot`.
+///
+/// This must only be called once; it will panic if it is called a second time.
+pub fn initialise(pci_info: PciInfo, memory: &mut MemoryTracker) -> Result<PciRoot, RebootReason> {
+    map_mmio(&pci_info, memory)?;
+
+    PCI_INFO.set(Box::new(pci_info.clone())).expect("Tried to set PCI_INFO a second time");
+
+    // Safety: This is the only place where we call make_pci_root, and `PCI_INFO.set` above will
+    // panic if it is called a second time.
+    Ok(unsafe { pci_info.make_pci_root() })
+}
+
 /// Maps the CAM and BAR range in the page table and MMIO guard.
-pub fn map_mmio(pci_info: &PciInfo, memory: &mut MemoryTracker) -> Result<(), RebootReason> {
+fn map_mmio(pci_info: &PciInfo, memory: &mut MemoryTracker) -> Result<(), RebootReason> {
     memory.map_mmio_range(pci_info.cam_range.clone()).map_err(|e| {
         error!("Failed to map PCI CAM: {}", e);
         RebootReason::InternalError