[PATCH v2 1/1] of: unittest: overlay: ensure proper alignment of copied FDT

[frowand . list]

From: Frank Rowand <frank.rowand@xxxxxxxx>

The Devicetree standard specifies an 8 byte alignment of the FDT.
Code in libfdt expects this alignment for an FDT image in memory.
kmemdup() returns 4 byte alignment on openrisc.  Replace kmemdup()
with kmalloc(), align pointer, memcpy() to get proper alignment.

The 4 byte alignment exposed a related bug which triggered a crash
on openrisc with:
commit 79edff12060f ("scripts/dtc: Update to upstream version v1.6.0-51-g183df9e9c2b9")
as reported in:
https://lore.kernel.org/lkml/20210327224116.69309-1-linux@xxxxxxxxxxxx/

Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxx>

---

Please review carefully, I am not yet fully awake...

changes since version 1:
  - use pointer from kmalloc() for kfree() instead of using pointer that
    has been modified for FDT alignment

 drivers/of/of_private.h |  2 ++
 drivers/of/overlay.c    | 28 +++++++++++++++++-----------
 drivers/of/unittest.c   | 12 +++++++++---
 3 files changed, 28 insertions(+), 14 deletions(-)

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index d9e6a324de0a..d717efbd637d 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -8,6 +8,8 @@
  * Copyright (C) 1996-2005 Paul Mackerras.
  */
 
+#define FDT_ALIGN_SIZE 8
+
 /**
  * struct alias_prop - Alias property in 'aliases' node
  * @link:	List node to link the structure in aliases_lookup list
diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 50bbe0edf538..e0397d70d531 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -57,7 +57,7 @@ struct fragment {
  * struct overlay_changeset
  * @id:			changeset identifier
  * @ovcs_list:		list on which we are located
- * @fdt:		FDT that was unflattened to create @overlay_tree
+ * @fdt:		base of memory allocated to hold aligned FDT that was unflattened to create @overlay_tree
  * @overlay_tree:	expanded device tree that contains the fragment nodes
  * @count:		count of fragment structures
  * @fragments:		fragment nodes in the overlay expanded device tree
@@ -719,8 +719,8 @@ static struct device_node *find_target(struct device_node *info_node)
 /**
  * init_overlay_changeset() - initialize overlay changeset from overlay tree
  * @ovcs:	Overlay changeset to build
- * @fdt:	the FDT that was unflattened to create @tree
- * @tree:	Contains all the overlay fragments and overlay fixup nodes
+ * @fdt:	base of memory allocated to hold aligned FDT that was unflattened to create @tree
+ * @tree:	Contains the overlay fragments and overlay fixup nodes
  *
  * Initialize @ovcs.  Populate @ovcs->fragments with node information from
  * the top level of @tree.  The relevant top level nodes are the fragment
@@ -873,7 +873,8 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
  * internal documentation
  *
  * of_overlay_apply() - Create and apply an overlay changeset
- * @fdt:	the FDT that was unflattened to create @tree
+ * @fdt_align:	the FDT that was unflattened to create @tree, aligned
+ * @fdt:	base of memory allocated to hold *@fdt_align
  * @tree:	Expanded overlay device tree
  * @ovcs_id:	Pointer to overlay changeset id
  *
@@ -912,8 +913,8 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
  * id is returned to *ovcs_id.
  */
 
-static int of_overlay_apply(const void *fdt, struct device_node *tree,
-		int *ovcs_id)
+static int of_overlay_apply(const void *fdt_align, const void *fdt,
+		struct device_node *tree, int *ovcs_id)
 {
 	struct overlay_changeset *ovcs;
 	int ret = 0, ret_revert, ret_tmp;
@@ -953,7 +954,7 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
 	/*
 	 * after overlay_notify(), ovcs->overlay_tree related pointers may have
 	 * leaked to drivers, so can not kfree() tree, aka ovcs->overlay_tree;
-	 * and can not free fdt, aka ovcs->fdt
+	 * and can not free memory containing aligned fdt, aka ovcs->fdt
 	 */
 	ret = overlay_notify(ovcs, OF_OVERLAY_PRE_APPLY);
 	if (ret) {
@@ -1014,7 +1015,8 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree,
 int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 			 int *ovcs_id)
 {
-	const void *new_fdt;
+	void *new_fdt;
+	void *new_fdt_align;
 	int ret;
 	u32 size;
 	struct device_node *overlay_root;
@@ -1036,18 +1038,22 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 	 * Must create permanent copy of FDT because of_fdt_unflatten_tree()
 	 * will create pointers to the passed in FDT in the unflattened tree.
 	 */
-	new_fdt = kmemdup(overlay_fdt, size, GFP_KERNEL);
+	size += FDT_ALIGN_SIZE;
+	new_fdt = kmalloc(size, GFP_KERNEL);
 	if (!new_fdt)
 		return -ENOMEM;
 
-	of_fdt_unflatten_tree(new_fdt, NULL, &overlay_root);
+	new_fdt_align = PTR_ALIGN(new_fdt, FDT_ALIGN_SIZE);
+	memcpy(new_fdt_align, overlay_fdt, size);
+
+	of_fdt_unflatten_tree(new_fdt_align, NULL, &overlay_root);
 	if (!overlay_root) {
 		pr_err("unable to unflatten overlay_fdt\n");
 		ret = -EINVAL;
 		goto out_free_new_fdt;
 	}
 
-	ret = of_overlay_apply(new_fdt, overlay_root, ovcs_id);
+	ret = of_overlay_apply(new_fdt_align, new_fdt, overlay_root, ovcs_id);
 	if (ret < 0) {
 		/*
 		 * new_fdt and overlay_root now belong to the overlay
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index eb100627c186..29081a8b32e6 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -22,6 +22,7 @@
 #include <linux/slab.h>
 #include <linux/device.h>
 #include <linux/platform_device.h>
+#include <linux/kernel.h>
 
 #include <linux/i2c.h>
 #include <linux/i2c-mux.h>
@@ -1408,6 +1409,7 @@ static void attach_node_and_children(struct device_node *np)
 static int __init unittest_data_add(void)
 {
 	void *unittest_data;
+	void *unittest_data_align;
 	struct device_node *unittest_data_node, *np;
 	/*
 	 * __dtb_testcases_begin[] and __dtb_testcases_end[] are magically
@@ -1415,7 +1417,7 @@ static int __init unittest_data_add(void)
 	 */
 	extern uint8_t __dtb_testcases_begin[];
 	extern uint8_t __dtb_testcases_end[];
-	const int size = __dtb_testcases_end - __dtb_testcases_begin;
+	u32 size = __dtb_testcases_end - __dtb_testcases_begin;
 	int rc;
 
 	if (!size) {
@@ -1425,11 +1427,15 @@ static int __init unittest_data_add(void)
 	}
 
 	/* creating copy */
-	unittest_data = kmemdup(__dtb_testcases_begin, size, GFP_KERNEL);
+	size += FDT_ALIGN_SIZE;
+	unittest_data = kmalloc(size, GFP_KERNEL);
 	if (!unittest_data)
 		return -ENOMEM;
 
-	of_fdt_unflatten_tree(unittest_data, NULL, &unittest_data_node);
+	unittest_data_align = PTR_ALIGN(unittest_data, FDT_ALIGN_SIZE);
+	memcpy(unittest_data_align, __dtb_testcases_begin, size);
+
+	of_fdt_unflatten_tree(unittest_data_align, NULL, &unittest_data_node);
 	if (!unittest_data_node) {
 		pr_warn("%s: No tree to attach; not running tests\n", __func__);
 		kfree(unittest_data);
-- 
Frank Rowand <frank.rowand@xxxxxxxx>