powerpc/book3s: Fix mc_recoverable_range buffer overrun issue.

Currently we wrongly allocate mc_recoverable_range buffer (to hold
recoverable ranges) based on size of the property "mcheck-recoverable-ranges".
This results in allocating less memory to hold available recoverable range
entries from /proc/device-tree/ibm,opal/mcheck-recoverable-ranges.

This patch fixes this issue by allocating mc_recoverable_range buffer based
on number of entries of recoverable ranges instead of device property size.
Without this change we end up allocating less memory and run into memory
corruption issue.
Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/powernv/opal.c

@@ -102,19 +102,36 @@ int __init early_init_dt_scan_opal(unsigned long node,
 int __init early_init_dt_scan_recoverable_ranges(unsigned long node,
 				   const char *uname, int depth, void *data)
 {
-	unsigned long i, size;
+	unsigned long i, psize, size;
 	const __be32 *prop;
 
 	if (depth != 1 || strcmp(uname, "ibm,opal") != 0)
 		return 0;
 
-	prop = of_get_flat_dt_prop(node, "mcheck-recoverable-ranges", &size);
+	prop = of_get_flat_dt_prop(node, "mcheck-recoverable-ranges", &psize);
 
 	if (!prop)
 		return 1;
 
 	pr_debug("Found machine check recoverable ranges.\n");
 
+	/*
+	 * Calculate number of available entries.
+	 *
+	 * Each recoverable address range entry is (start address, len,
+	 * recovery address), 2 cells each for start and recovery address,
+	 * 1 cell for len, totalling 5 cells per entry.
+	 */
+	mc_recoverable_range_len = psize / (sizeof(*prop) * 5);
+
+	/* Sanity check */
+	if (!mc_recoverable_range_len)
+		return 1;
+
+	/* Size required to hold all the entries. */
+	size = mc_recoverable_range_len *
+			sizeof(struct mcheck_recoverable_range);
+
 	/*
 	 * Allocate a buffer to hold the MC recoverable ranges. We would be
 	 * accessing them in real mode, hence it needs to be within
@@ -124,11 +141,7 @@ int __init early_init_dt_scan_recoverable_ranges(unsigned long node,
 							ppc64_rma_size));
 	memset(mc_recoverable_range, 0, size);
 
-	/*
-	 * Each recoverable address entry is an (start address,len,
-	 * recover address) pair, * 2 cells each, totalling 4 cells per entry.
-	 */
-	for (i = 0; i < size / (sizeof(*prop) * 5); i++) {
+	for (i = 0; i < mc_recoverable_range_len; i++) {
 		mc_recoverable_range[i].start_addr =
 					of_read_number(prop + (i * 5) + 0, 2);
 		mc_recoverable_range[i].end_addr =
@@ -142,7 +155,6 @@ int __init early_init_dt_scan_recoverable_ranges(unsigned long node,
 				mc_recoverable_range[i].end_addr,
 				mc_recoverable_range[i].recover_addr);
 	}
-	mc_recoverable_range_len = i;
 	return 1;
 }