lib/mpi: Endianness fix

The limbs are integers in the host endianness, so we can't simply
iterate over the individual bytes. The current code happens to work on
little-endian, because the order of the limbs in the MPI array is the
same as the order of the bytes in each limb, but it breaks on
big-endian.

Fixes: 0f74fbf77d45 ("MPI: Fix mpi_read_buffer")
Signed-off-by: Michal Marek <mmarek@suse.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 21 insertions, 18 deletions

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index ec533a6c77b5..eb15e7dc7b65 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -128,6 +128,23 @@ leave:
 }
 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 
+static int count_lzeros(MPI a)
+{
+        mpi_limb_t alimb;
+        int i, lzeros = 0;
+
+        for (i = a->nlimbs - 1; i >= 0; i--) {
+                alimb = a->d[i];
+                if (alimb == 0) {
+                        lzeros += sizeof(mpi_limb_t);
+                } else {
+                        lzeros += count_leading_zeros(alimb) / 8;
+                        break;
+                }
+        }
+        return lzeros;
+}
+
 /**
  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
  *
@@ -148,7 +165,7 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
         uint8_t *p;
         mpi_limb_t alimb;
         unsigned int n = mpi_get_size(a);
-        int i, lzeros = 0;
+        int i, lzeros;
 
         if (!buf || !nbytes)
                 return -EINVAL;
@@ -156,14 +173,7 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
         if (sign)
                 *sign = a->sign;
 
-        p = (void *)&a->d[a->nlimbs] - 1;
-
-        for (i = a->nlimbs * sizeof(alimb) - 1; i >= 0; i--, p--) {
-                if (!*p)
-                        lzeros++;
-                else
-                        break;
-        }
+        lzeros = count_lzeros(a);
 
         if (buf_len < n - lzeros) {
                 *nbytes = n - lzeros;
@@ -351,7 +361,7 @@ int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
         u8 *p, *p2;
         mpi_limb_t alimb, alimb2;
         unsigned int n = mpi_get_size(a);
-        int i, x, y = 0, lzeros = 0, buf_len;
+        int i, x, y = 0, lzeros, buf_len;
 
         if (!nbytes)
                 return -EINVAL;
@@ -359,14 +369,7 @@ int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
         if (sign)
                 *sign = a->sign;
 
-        p = (void *)&a->d[a->nlimbs] - 1;
-
-        for (i = a->nlimbs * sizeof(alimb) - 1; i >= 0; i--, p--) {
-                if (!*p)
-                        lzeros++;
-                else
-                        break;
-        }
+        lzeros = count_lzeros(a);
 
         if (*nbytes < n - lzeros) {
                 *nbytes = n - lzeros;