Patch "ARM: 8616/1: dt: Respect property size when parsing CPUs" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ARM: 8616/1: dt: Respect property size when parsing CPUs

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     arm-8616-1-dt-respect-property-size-when-parsing-cpus.patch

and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Robin Murphy <[email protected]>
Date: Mon, 26 Sep 2016 16:50:55 +0100
Subject: ARM: 8616/1: dt: Respect property size when parsing CPUs

From: Robin Murphy <[email protected]>

commit ba6dea4f7cedb4b1c17e36f4087675d817c2e24b upstream.

Whilst MPIDR values themselves are less than 32 bits, it is still perfectly valid for a DT to have #address-cells > 1 in the CPUs node, resulting in the "reg" property having leading zero cell(s). In that situation, the big-endian nature of the data conspires with the current behaviour of only reading the first cell to cause the kernel to think all CPUs have ID 0, and become resoundingly unhappy as a consequence.

Take the full property length into account when parsing CPUs so as to be correct under any circumstances.

---
 arch/arm/kernel/devtree.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

@@ -87,6 +87,8 @@ void __init arm_dt_init_cpu_maps(void)
 		return;
 
 	for_each_child_of_node(cpus, cpu) {
+		const __be32 *cell;
+		int prop_bytes;
 		u32 hwid;
 
 		if (of_node_cmp(cpu->type, "cpu"))

@@ -98,7 +100,8 @@ void __init arm_dt_init_cpu_maps(void)
 		 * properties is considered invalid to build the
 		 * cpu_logical_map.
 		 */
-		if (of_property_read_u32(cpu, "reg", &hwid)) {
+		cell = of_get_property(cpu, "reg", &prop_bytes);
+		if (!cell || prop_bytes < sizeof(*cell)) {
 			pr_debug(" * %s missing reg property\n",
 				     cpu->full_name);
 			of_node_put(cpu);

@@ -106,10 +109,15 @@ void __init arm_dt_init_cpu_maps(void)
 		}
 
 		/*
-		 * 8 MSBs must be set to 0 in the DT since the reg property
+		 * Bits n:24 must be set to 0 in the DT since the reg property
 		 * defines the MPIDR[23:0].
 		 */
-		if (hwid & ~MPIDR_HWID_BITMASK) {
+		do {
+			hwid = be32_to_cpu(*cell++);
+			prop_bytes -= sizeof(*cell);
+		} while (!hwid && prop_bytes > 0);
+
+		if (prop_bytes || (hwid & ~MPIDR_HWID_BITMASK)) {
 			of_node_put(cpu);
 			return;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/arm-8616-1-dt-respect-property-size-when-parsing-cpus.patch