[PATCH] ipv6: Ensure natural alignment of const ipv6 loopback and router addresses

[PATCH] ipv6: Ensure natural alignment of const ipv6 loopback and router addresses

[Helge Deller]

On a parisc64 kernel I notice sometimes this kernel warning:
Kernel unaligned access to 0x40ff8814 at ndisc_send_skb+0xc0/0x4d8

The address 0x40ff8814 points to the in6addr_linklocal_allrouters
variable and the warning simply means that some ipv6 function tries to
read a 64-bit word directly from the not-64-bit aligned
in6addr_linklocal_allrouters variable.

The patch below ensures that those ipv6 loopback and router addresses
always will be naturally aligned and as such prevents unaligned accesses
for all architectures.

Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/net/ipv6/addrconf_core.c b/net/ipv6/addrconf_core.c
index 507a8353a6bd..813e009b4d0e 100644
--- a/net/ipv6/addrconf_core.c
+++ b/net/ipv6/addrconf_core.c
@@ -220,19 +220,26 @@ const struct ipv6_stub *ipv6_stub __read_mostly = &(struct ipv6_stub) {
 EXPORT_SYMBOL_GPL(ipv6_stub);
 
 /* IPv6 Wildcard Address and Loopback Address defined by RFC2553 */
-const struct in6_addr in6addr_loopback = IN6ADDR_LOOPBACK_INIT;
+const struct in6_addr in6addr_loopback __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_LOOPBACK_INIT;
 EXPORT_SYMBOL(in6addr_loopback);
-const struct in6_addr in6addr_any = IN6ADDR_ANY_INIT;
+const struct in6_addr in6addr_any __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_ANY_INIT;
 EXPORT_SYMBOL(in6addr_any);
-const struct in6_addr in6addr_linklocal_allnodes = IN6ADDR_LINKLOCAL_ALLNODES_INIT;
+const struct in6_addr in6addr_linklocal_allnodes __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_LINKLOCAL_ALLNODES_INIT;
 EXPORT_SYMBOL(in6addr_linklocal_allnodes);
-const struct in6_addr in6addr_linklocal_allrouters = IN6ADDR_LINKLOCAL_ALLROUTERS_INIT;
+const struct in6_addr in6addr_linklocal_allrouters __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_LINKLOCAL_ALLROUTERS_INIT;
 EXPORT_SYMBOL(in6addr_linklocal_allrouters);
-const struct in6_addr in6addr_interfacelocal_allnodes = IN6ADDR_INTERFACELOCAL_ALLNODES_INIT;
+const struct in6_addr in6addr_interfacelocal_allnodes __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_INTERFACELOCAL_ALLNODES_INIT;
 EXPORT_SYMBOL(in6addr_interfacelocal_allnodes);
-const struct in6_addr in6addr_interfacelocal_allrouters = IN6ADDR_INTERFACELOCAL_ALLROUTERS_INIT;
+const struct in6_addr in6addr_interfacelocal_allrouters __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_INTERFACELOCAL_ALLROUTERS_INIT;
 EXPORT_SYMBOL(in6addr_interfacelocal_allrouters);
-const struct in6_addr in6addr_sitelocal_allrouters = IN6ADDR_SITELOCAL_ALLROUTERS_INIT;
+const struct in6_addr in6addr_sitelocal_allrouters __aligned(BITS_PER_LONG/8)
+	= IN6ADDR_SITELOCAL_ALLROUTERS_INIT;
 EXPORT_SYMBOL(in6addr_sitelocal_allrouters);
 
 static void snmp6_free_dev(struct inet6_dev *idev)

Re: [PATCH] ipv6: Ensure natural alignment of const ipv6 loopback and router addresses

[Paolo Abeni]

On Mon, 2024-01-22 at 22:27 +0100, Helge Deller wrote:
> On a parisc64 kernel I notice sometimes this kernel warning:
> Kernel unaligned access to 0x40ff8814 at ndisc_send_skb+0xc0/0x4d8
> 
> The address 0x40ff8814 points to the in6addr_linklocal_allrouters
> variable and the warning simply means that some ipv6 function tries to
> read a 64-bit word directly from the not-64-bit aligned
> in6addr_linklocal_allrouters variable.
> 
> The patch below ensures that those ipv6 loopback and router addresses
> always will be naturally aligned and as such prevents unaligned accesses
> for all architectures.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>

The patch LGTM, but the above looks like material for the 'net' tree,
would you mind sending a v2 including a relevant fixes tag, the target
tree in the subject prefix and possibly the stacktrace you observe?

Feel free to include my acked-by tag in v2.

Thanks,

Paolo