lib/mpi: Fix kernel unaligned access in mpi_write_to_sgl

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.

---
v2: tadeusz.struk comments: Predicate on BYTES_PER_MPI_LIMB.

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

index eb15e7d..b61eb6b 100644
@@ -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

Please cc linux-crypto.

Thanks,

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Just bounced the message to linux-crypto as well. I think get_maintainers.pl might also need to be updated to generate this automatically.

Thanks,
--Sowmini

Sorry, but your patch doesn't apply against the current tree at all. Please rebase it if it is still needed.

Thanks,

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Hello,

I had based my patch off of net-next, which is where I do my work.

I'd be happy to rebase it on the "current tree",
but given that mpicoder.c does not have an entry in MAINTAINERS, please clarify what you mean by "current tree" in this case.

do you mean

git://git.kernel.org/pub/scm/linux/kernel/git/herbert/cryptodev-2.6.git
or
git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6.git
or
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

(which are the three possible candidates I can see in MAINTAINERS).

It would be nice to get this bug fixed, since the fix is fairly obvious, and the nuisance factor from the generated "unaligned access" messages on the impacted non-intel platforms is quite high,

thanks,
--Sowmini

Please base it on cryptodev.

Thanks,

Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Looks like this got fixed in cryptodev by commit cece762f6f3c ("lib/mpi: mpi_write_sgl(): fix out-of-bounds stack access")

Thanks,
--Sowmini