ipv6: Ensure natural alignment of const ipv6 loopback and router addresses

stable inclusion
from stable-v4.19.307
commit e6b0f4f7e3b2429d78a54ad5ec705b4119010c32
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I970CO


CVE: NA

--------------------------------

[ Upstream commit 60365049ccbacd101654a66ddcb299abfabd4fc5 ]

On a parisc64 kernel I sometimes notice 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.

Unaligned accesses are non-critical as the architecture or exception
handlers usually will fix it up at runtime. Nevertheless it may trigger
a performance penality for some architectures. For details read the
"unaligned-memory-access" kernel documentation.

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

Signed-off-by: Helge Deller <deller@gmx.de>
Fixes: 034dfc5d ("ipv6: export in6addr_loopback to modules")
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://lore.kernel.org/r/ZbNuFM1bFqoH-UoY@p100


Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>