of: unittest: overlay: ensure proper alignment of copied FDT

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@roeck-us.net/

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Link: https://lore.kernel.org/r/20210408204508.2276230-1-frowand.list@gmail.com
Signed-off-by: Rob Herring <robh@kernel.org>

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index d9e6a32..d717efb 100644 (file)
--- 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 e12c643..23effe5 100644 (file)
--- 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 +873,7 @@ 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:       base of memory allocated to hold the aligned FDT
  * @tree:      Expanded overlay device tree
  * @ovcs_id:   Pointer to overlay changeset id
  *
@@ -953,7 +953,9 @@ 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.  The aligned fdt
+        * is contained within the memory at ovcs->fdt, possibly at an offset
+        * from ovcs->fdt.
         */
        ret = overlay_notify(ovcs, OF_OVERLAY_PRE_APPLY);
        if (ret) {
@@ -1014,7 +1016,8 @@ out:
 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 = NULL;
@@ -1036,11 +1039,14 @@ 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);
+       new_fdt = kmalloc(size + FDT_ALIGN_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;

diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index f9b5b69..819a20a 100644 (file)
--- 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 = NULL, *np;
        /*
         * __dtb_testcases_begin[] and __dtb_testcases_end[] are magically
@@ -1425,11 +1427,14 @@ static int __init unittest_data_add(void)
        }
 
        /* creating copy */
-       unittest_data = kmemdup(__dtb_testcases_begin, size, GFP_KERNEL);
+       unittest_data = kmalloc(size + FDT_ALIGN_SIZE, GFP_KERNEL);
        if (!unittest_data)
                return -ENOMEM;
 
-       ret = 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);
+
+       ret = of_fdt_unflatten_tree(unittest_data_align, NULL, &unittest_data_node);
        if (!ret) {
                pr_warn("%s: unflatten testcases tree failed\n", __func__);
                kfree(unittest_data);