linux-kernel - [PATCH 1/1] of: unittest: overlay: ensure proper alignment of copied FDT

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Message-Id: <20210407205110.2173976-1-frowand.list@gmail.com>
Date:   Wed,  7 Apr 2021 15:51:10 -0500
From:   frowand.list@...il.com
To:     Rob Herring <robh+dt@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        devicetree@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] of: unittest: overlay: ensure proper alignment of copied FDT

From: Frank Rowand <frank.rowand@...y.com>

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@...ck-us.net>
Signed-off-by: Frank Rowand <frank.rowand@...y.com>
---
 drivers/of/of_private.h | 2 ++
 drivers/of/overlay.c    | 8 ++++++--
 drivers/of/unittest.c   | 9 +++++++--
 3 files changed, 15 insertions(+), 4 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..8b40711ed202 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -1014,7 +1014,7 @@ 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;
 	int ret;
 	u32 size;
 	struct device_node *overlay_root;
@@ -1036,10 +1036,14 @@ 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);
+	size += FDT_ALIGN_SIZE;
+	new_fdt = kmalloc(size, GFP_KERNEL);
 	if (!new_fdt)
 		return -ENOMEM;
 
+	new_fdt = PTR_ALIGN(new_fdt, FDT_ALIGN_SIZE);
+	memcpy(new_fdt, overlay_fdt, size);
+
 	of_fdt_unflatten_tree(new_fdt, NULL, &overlay_root);
 	if (!overlay_root) {
 		pr_err("unable to unflatten overlay_fdt\n");
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index eb100627c186..edd6ce807691 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>
@@ -1415,7 +1416,7 @@ 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) {
@@ -1425,10 +1426,14 @@ 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;
 
+	unittest_data = PTR_ALIGN(unittest_data, FDT_ALIGN_SIZE);
+	memcpy(unittest_data, __dtb_testcases_begin, size);
+
 	of_fdt_unflatten_tree(unittest_data, NULL, &unittest_data_node);
 	if (!unittest_data_node) {
 		pr_warn("%s: No tree to attach; not running tests\n", __func__);
-- 
Frank Rowand <frank.rowand@...y.com>