linux-kernel - [PATCH V2 XRT Alveo Infrastructure 3/9] of: handle fdt buffer alignment inside unflatten function

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Date:   Fri, 19 Nov 2021 14:24:06 -0800
From:   Lizhi Hou <lizhi.hou@...inx.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Lizhi Hou <lizhi.hou@...inx.com>, <linux-fpga@...r.kernel.org>,
        <maxz@...inx.com>, <sonal.santan@...inx.com>, <yliu@...inx.com>,
        <michal.simek@...inx.com>, <stefanos@...inx.com>,
        <devicetree@...r.kernel.org>, <trix@...hat.com>, <mdf@...nel.org>,
        <robh@...nel.org>, <dwmw2@...radead.org>,
        Max Zhen <max.zhen@...inx.com>
Subject: [PATCH V2 XRT Alveo Infrastructure 3/9] of: handle fdt buffer alignment inside unflatten function

Add alignment check to of_fdt_unflatten_tree(). If it is not aligned,
allocate a aligned buffer and copy the fdt blob. So the caller does not
have to deal with the buffer alignment before calling this function.
XRT uses this function to unflatten fdt which is from Alveo firmware.

Signed-off-by: Sonal Santan <sonal.santan@...inx.com>
Signed-off-by: Max Zhen <max.zhen@...inx.com>
Signed-off-by: Lizhi Hou <lizhi.hou@...inx.com>
---
 drivers/of/fdt.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 4546572af24b..d64445e43ceb 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -455,13 +455,28 @@ void *of_fdt_unflatten_tree(const unsigned long *blob,
 			    struct device_node *dad,
 			    struct device_node **mynodes)
 {
+	void *new_fdt = NULL, *fdt_align;
 	void *mem;
 
+	if (fdt_check_header(blob)) {
+		pr_err("Invalid fdt blob\n");
+		return NULL;
+	}
+	fdt_align = (void *)PTR_ALIGN(blob, FDT_ALIGN_SIZE);
+	if (fdt_align != blob) {
+		new_fdt = kmalloc(fdt_totalsize(blob) + FDT_ALIGN_SIZE, GFP_KERNEL);
+		if (!new_fdt)
+			return NULL;
+		fdt_align = PTR_ALIGN(new_fdt, FDT_ALIGN_SIZE);
+	}
+
 	mutex_lock(&of_fdt_unflatten_mutex);
-	mem = __unflatten_device_tree(blob, dad, mynodes, &kernel_tree_alloc,
+	mem = __unflatten_device_tree(fdt_align, dad, mynodes, &kernel_tree_alloc,
 				      true);
 	mutex_unlock(&of_fdt_unflatten_mutex);
 
+	kfree(new_fdt);
+
 	return mem;
 }
 EXPORT_SYMBOL_GPL(of_fdt_unflatten_tree);
-- 
2.27.0