[PATCH for-4.20 v2] xen/arm: bootfdt: Fix device tree memory node probing

[Michal Orzel <michal.orzel@xxxxxxx>]

Memory node probing is done as part of early_scan_node() that is called
for each node with depth >= 1 (root node is at depth 0). According to
Devicetree Specification v0.4, chapter 3.4, /memory node can only exists
as a top level node. However, Xen incorrectly considers all the nodes with
unit node name "memory" as RAM. This buggy behavior can result in a
failure if there are other nodes in the device tree (at depth >= 2) with
"memory" as unit node name. An example can be a "memory@xxx" node under
/reserved-memory. Fix it by introducing device_tree_is_memory_node() to
perform all the required checks to assess if a node is a proper /memory
node.

Fixes: 3e99c95ba1c8 ("arm, device tree: parse the DTB for RAM location and 
size")
Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
Tested-by: Luca Fancellu <luca.fancellu@xxxxxxx>
---
Changes in v2:
 - improve the length check
---
 xen/arch/arm/bootfdt.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/bootfdt.c b/xen/arch/arm/bootfdt.c
index 6e060111d95b..f2892fce0a9c 100644
--- a/xen/arch/arm/bootfdt.c
+++ b/xen/arch/arm/bootfdt.c
@@ -83,6 +83,32 @@ static bool __init device_tree_node_compatible(const void 
*fdt, int node,
     return false;
 }
 
+/*
+ * Check if a node is a proper /memory node according to Devicetree
+ * Specification v0.4, chapter 3.4.
+ */
+static bool __init device_tree_is_memory_node(const void *fdt, int node,
+                                              int depth)
+{
+    const char *type;
+    int len;
+
+    if ( depth != 1 )
+        return false;
+
+    if ( !device_tree_node_matches(fdt, node, "memory") )
+        return false;
+
+    type = fdt_getprop(fdt, node, "device_type", &len);
+    if ( !type )
+        return false;
+
+    if ( (len <= strlen("memory")) || strcmp(type, "memory") )
+        return false;
+
+    return true;
+}
+
 void __init device_tree_get_reg(const __be32 **cell, uint32_t address_cells,
                                 uint32_t size_cells, paddr_t *start,
                                 paddr_t *size)
@@ -448,7 +474,7 @@ static int __init early_scan_node(const void *fdt,
      * populated. So we should skip the parsing.
      */
     if ( !efi_enabled(EFI_BOOT) &&
-         device_tree_node_matches(fdt, node, "memory") )
+         device_tree_is_memory_node(fdt, node, depth) )
         rc = process_memory_node(fdt, node, name, depth,
                                  address_cells, size_cells, 
bootinfo_get_mem());
     else if ( depth == 1 && !dt_node_cmp(name, "reserved-memory") )
-- 
2.25.1