[PATCH v2 2/3] KVM: arm64: disown unused reserved-memory regions

[Peter Collingbourne]

The meaning of no-map on a reserved-memory node is as follows:

      Indicates the operating system must not create a virtual mapping
      of the region as part of its standard mapping of system memory,
      nor permit speculative access to it under any circumstances other
      than under the control of the device driver using the region.

If there is no compatible property, there is no device driver, so the
host kernel has no business accessing the reserved-memory region. Since
these regions may represent a route through which the host kernel
can gain additional privileges, disown any such memory regions before
deprivileging ourselves.

Signed-off-by: Peter Collingbourne <pcc at google.com>
---
 arch/arm64/kvm/arm.c | 46 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index c1fc4ef82f93..91ca128e7daa 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -4,6 +4,7 @@
  * Author: Christoffer Dall <c.dall at virtualopensystems.com>
  */
 
+#include <linux/acpi.h>
 #include <linux/bug.h>
 #include <linux/cpu_pm.h>
 #include <linux/entry-kvm.h>
@@ -12,6 +13,7 @@
 #include <linux/kvm_host.h>
 #include <linux/list.h>
 #include <linux/module.h>
+#include <linux/of.h>
 #include <linux/vmalloc.h>
 #include <linux/fs.h>
 #include <linux/mman.h>
@@ -1913,6 +1915,48 @@ static bool init_psci_relay(void)
 	return true;
 }
 
+static void disown_reserved_memory(struct device_node *node)
+{
+	int addr_cells = of_n_addr_cells(node);
+	int size_cells = of_n_size_cells(node);
+	const __be32 *reg, *end;
+	int len;
+
+	reg = of_get_property(node, "reg", &len);
+	if (len % (4 * (addr_cells + size_cells)))
+		return;
+
+	end = reg + (len / 4);
+	while (reg != end) {
+		u64 addr, size;
+
+		addr = of_read_number(reg, addr_cells);
+		reg += addr_cells;
+		size = of_read_number(reg, size_cells);
+		reg += size_cells;
+
+		kvm_call_hyp_nvhe(__pkvm_disown_pages, addr, size);
+	}
+}
+
+static void kvm_reserved_memory_init(void)
+{
+	struct device_node *parent, *node;
+
+	if (!acpi_disabled || !is_protected_kvm_enabled())
+		return;
+
+	parent = of_find_node_by_path("/reserved-memory");
+	if (!parent)
+		return;
+
+	for_each_child_of_node(parent, node) {
+		if (!of_get_property(node, "compatible", NULL) &&
+		    of_get_property(node, "no-map", NULL))
+			disown_reserved_memory(node);
+	}
+}
+
 static int init_subsystems(void)
 {
 	int err = 0;
@@ -1953,6 +1997,8 @@ static int init_subsystems(void)
 
 	kvm_register_perf_callbacks(NULL);
 
+	kvm_reserved_memory_init();
+
 out:
 	if (err || !is_protected_kvm_enabled())
 		on_each_cpu(_kvm_arch_hardware_disable, NULL, 1);
-- 
2.37.0.144.g8ac04bfd2-goog