From: Steffen Klassert <steffen.klassert@secunet.com>
Date: Wed, 21 Oct 2015 08:57:04 +0200

On Mon, Oct 19, 2015 at 05:23:29PM -0400, Sowmini Varadhan wrote:

quoted

On sparc, deleting established SAs (e.g., by restarting ipsec
at the peer) results in unaligned access messages via
xfrm_del_sa -> km_state_notify -> xfrm_send_state_notify().
Use an aligned pointer to xfrm_usersa_info for this case.

Signed-off-by: Sowmini Varadhan <redacted>
---
 net/xfrm/xfrm_user.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index a8de9e3..158ef4a 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c

@@ -2659,7 +2659,7 @@ static int xfrm_notify_sa(struct xfrm_state *x, const struct km_event *c)
 		if (attr == NULL)
 			goto out_free_skb;
 
-		p = nla_data(attr);
+		p = PTR_ALIGN(nla_data(attr), __alignof__(*p));

Hm, this breaks userspace notifications on 64-bit systems.
Userspace expects this to be aligned to 4, with your patch
it is aligned to 8 on 64-bit.

That's correct, netlink attributes are fundamentally only 4 byte
aligned and this cannot be changed.  nla_data() is exactly
where the attribute must be placed, aligned or not.

The only workaround is, when designing netlink attributes.  Various
netlink libraries have workarounds for accessing, for example, 64-bit
stats which are going to be unaligned in netlink messages.