[PATCH v2] lib/mpi: Fix kernel unaligned access in mpi_write_to_sgl

[Sowmini Varadhan <sowmini.varadhan@oracle.com>]

Commit 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers") added
mpi_write_to_sgl() which generates traps due to unaligned
access on some platforms like sparc. Fix this by using
the get_unaligned* and put_unaligned* functions.

Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
v2: tadeusz.struk comments: Predicate on BYTES_PER_MPI_LIMB.

 lib/mpi/mpicoder.c |   21 +++++++++++++++++----
 1 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index eb15e7d..b61eb6b 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -21,6 +21,7 @@
 #include <linux/bitops.h>
 #include <linux/count_zeros.h>
 #include "mpi-internal.h"
+#include <asm/unaligned.h>
 
 #define MAX_EXTERN_MPI_BITS 16384
 
@@ -405,10 +406,22 @@ int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 				p -= sizeof(alimb);
 				continue;
 			} else {
-				mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
-				mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
-							+ lzeros;
-				*limb1 = *limb2;
+				mpi_limb_t tmp;
+#if BYTES_PER_MPI_LIMB == 4
+				tmp = get_unaligned_be32((void *)p -
+							 sizeof(alimb) +
+							 lzeros);
+				put_unaligned_be32(tmp, (void *)p -
+						   sizeof(alimb));
+#elif BYTES_PER_MPI_LIMB == 8
+				tmp = get_unaligned_be64((void *)p -
+							 sizeof(alimb) +
+							 lzeros);
+				put_unaligned_be64(tmp, (void *)p -
+						   sizeof(alimb));
+#else
+#error please implement for this limb size.
+#endif
 				p -= lzeros;
 				y = lzeros;
 			}
-- 
1.7.1