crypto: Work around deallocated stack frame reference gcc bug on sparc.

On sparc, if we have an alloca() like situation, as is the case with
SHASH_DESC_ON_STACK(), we can end up referencing deallocated stack
memory.  The result can be that the value is clobbered if a trap
or interrupt arrives at just the right instruction.

It only occurs if the function ends returning a value from that
alloca() area and that value can be placed into the return value
register using a single instruction.

For example, in lib/libcrc32c.c:crc32c() we end up with a return
sequence like:

        return  %i7+8
         lduw   [%o5+16], %o0   ! MEM[(u32 *)__shash_desc.1_10 + 16B],

%o5 holds the base of the on-stack area allocated for the shash
descriptor.  But the return released the stack frame and the
register window.

So if an intererupt arrives between 'return' and 'lduw', then
the value read at %o5+16 can be corrupted.

Add a data compiler barrier to work around this problem.  This is
exactly what the gcc fix will end up doing as well, and it absolutely
should not change the code generated for other cpus (unless gcc
on them has the same bug :-)

With crucial insight from Eric Sandeen.

Cc: <stable@vger.kernel.org>
Reported-by: Anatoly Pugachev <matorola@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/infiniband/sw/rxe/rxe.h b/drivers/infiniband/sw/rxe/rxe.h
index ecdba2fce083..1ac5b8551a4d 100644
--- a/drivers/infiniband/sw/rxe/rxe.h
+++ b/drivers/infiniband/sw/rxe/rxe.h
@@ -68,6 +68,7 @@
 static inline u32 rxe_crc32(struct rxe_dev *rxe,
 			    u32 crc, void *next, size_t len)
 {
+	u32 retval;
 	int err;
 
 	SHASH_DESC_ON_STACK(shash, rxe->tfm);
@@ -81,7 +82,9 @@ static inline u32 rxe_crc32(struct rxe_dev *rxe,
 		return crc32_le(crc, next, len);
 	}
 
-	return *(u32 *)shash_desc_ctx(shash);
+	retval = *(u32 *)shash_desc_ctx(shash);
+	barrier_data(shash_desc_ctx(shash));
+	return retval;
 }
 
 int rxe_set_mtu(struct rxe_dev *rxe, unsigned int dev_mtu);