powerpc/pseries/energy: Use OF accessor functions to read ibm,drc-indexes

In cpu_to_drc_index() in the case when FW_FEATURE_DRC_INFO is absent,
we currently use of_read_property() to obtain the pointer to the array
corresponding to the property "ibm,drc-indexes". The elements of this
array are of type __be32, but are accessed without any conversion to
the OS-endianness, which is buggy on a Little Endian OS.

Fix this by using of_property_read_u32_index() accessor function to
safely read the elements of the array.

Fixes: e83636ac3334 ("pseries/drc-info: Search DRC properties for CPU indexes")
Cc: stable@vger.kernel.org # v4.16+
Reported-by: Pavithra R. Prakash <pavrampu@in.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
[mpe: Make the WARN_ON a WARN_ON_ONCE so it's not retriggerable]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 18 insertions, 9 deletions

diff --git a/arch/powerpc/platforms/pseries/pseries_energy.c b/arch/powerpc/platforms/pseries/pseries_energy.c
index 6ed22127391b..921f12182f3e 100644
--- a/arch/powerpc/platforms/pseries/pseries_energy.c
+++ b/arch/powerpc/platforms/pseries/pseries_energy.c
@@ -77,18 +77,27 @@ static u32 cpu_to_drc_index(int cpu)
 
                 ret = drc.drc_index_start + (thread_index * drc.sequential_inc);
         } else {
-                const __be32 *indexes;
-
-                indexes = of_get_property(dn, "ibm,drc-indexes", NULL);
-                if (indexes == NULL)
-                        goto err_of_node_put;
+                u32 nr_drc_indexes, thread_drc_index;
 
                 /*
-                 * The first element indexes[0] is the number of drc_indexes
-                 * returned in the list.  Hence thread_index+1 will get the
-                 * drc_index corresponding to core number thread_index.
+                 * The first element of ibm,drc-indexes array is the
+                 * number of drc_indexes returned in the list.  Hence
+                 * thread_index+1 will get the drc_index corresponding
+                 * to core number thread_index.
                  */
-                ret = indexes[thread_index + 1];
+                rc = of_property_read_u32_index(dn, "ibm,drc-indexes",
+                                                0, &nr_drc_indexes);
+                if (rc)
+                        goto err_of_node_put;
+
+                WARN_ON_ONCE(thread_index > nr_drc_indexes);
+                rc = of_property_read_u32_index(dn, "ibm,drc-indexes",
+                                                thread_index + 1,
+                                                &thread_drc_index);
+                if (rc)
+                        goto err_of_node_put;
+
+                ret = thread_drc_index;
         }
 
         rc = 0;