1 files changed, 39 insertions, 15 deletions

diff --git a/kernel/resource.c b/kernel/resource.c
index ca9f5198a01f..5ad3eba619ba 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -73,6 +73,18 @@ static struct resource *next_resource(struct resource *p)
 	return p->sibling;
 }
 
+static struct resource *next_resource_skip_children(struct resource *p)
+{
+	while (!p->sibling && p->parent)
+		p = p->parent;
+	return p->sibling;
+}
+
+#define for_each_resource(_root, _p, _skip_children) \
+	for ((_p) = (_root)->child; (_p); \
+	     (_p) = (_skip_children) ? next_resource_skip_children(_p) : \
+				       next_resource(_p))
+
 static void *r_next(struct seq_file *m, void *v, loff_t *pos)
 {
 	struct resource *p = v;
@@ -1707,37 +1719,49 @@ static int strict_iomem_checks;
 #endif
 
 /*
- * check if an address is reserved in the iomem resource tree
- * returns true if reserved, false if not reserved.
+ * Check if an address is exclusive to the kernel and must not be mapped to
+ * user space, for example, via /dev/mem.
+ *
+ * Returns true if exclusive to the kernel, otherwise returns false.
  */
 bool iomem_is_exclusive(u64 addr)
 {
-	struct resource *p = &iomem_resource;
-	bool err = false;
-	loff_t l;
+	const unsigned int exclusive_system_ram = IORESOURCE_SYSTEM_RAM |
+						  IORESOURCE_EXCLUSIVE;
+	bool skip_children = false, err = false;
 	int size = PAGE_SIZE;
-
-	if (!strict_iomem_checks)
-		return false;
+	struct resource *p;
 
 	addr = addr & PAGE_MASK;
 
 	read_lock(&resource_lock);
-	for (p = p->child; p ; p = r_next(NULL, p, &l)) {
-		/*
-		 * We can probably skip the resources without
-		 * IORESOURCE_IO attribute?
-		 */
+	for_each_resource(&iomem_resource, p, skip_children) {
 		if (p->start >= addr + size)
 			break;
-		if (p->end < addr)
+		if (p->end < addr) {
+			skip_children = true;
 			continue;
+		}
+		skip_children = false;
+
+		/*
+		 * IORESOURCE_SYSTEM_RAM resources are exclusive if
+		 * IORESOURCE_EXCLUSIVE is set, even if they
+		 * are not busy and even if "iomem=relaxed" is set. The
+		 * responsible driver dynamically adds/removes system RAM within
+		 * such an area and uncontrolled access is dangerous.
+		 */
+		if ((p->flags & exclusive_system_ram) == exclusive_system_ram) {
+			err = true;
+			break;
+		}
+
 		/*
 		 * A resource is exclusive if IORESOURCE_EXCLUSIVE is set
 		 * or CONFIG_IO_STRICT_DEVMEM is enabled and the
 		 * resource is busy.
 		 */
-		if ((p->flags & IORESOURCE_BUSY) == 0)
+		if (!strict_iomem_checks || !(p->flags & IORESOURCE_BUSY))
 			continue;
 		if (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM)
 				|| p->flags & IORESOURCE_EXCLUSIVE) {