On 8/14/24 14:24, Dumitru Ceara wrote:
> Hi Ilya,
>
> On 8/14/24 14:09, Simon Horman wrote:
>> On Wed, Aug 14, 2024 at 12:35:28PM +0200, Ilya Maximets wrote:
>>> memcpy() is allowed to make alignment assumptions based on the argument
>>> type. We have to cast before using it to avoid misaligned reads:
>
> I guess that's fine. But I'm not sure I understand how memcpy() is
> allowed to make any assumption based on the argument type. Isn't
> memcpy() supposed to be a function call?
>
> At least the man page on my machine says:
>
> NAME
> memcpy - copy memory area
>
> LIBRARY
> Standard C library (libc, -lc)
>
> SYNOPSIS
> #include <string.h>
>
> void *memcpy(void dest[restrict .n], const void src[restrict .n],
> size_t n);
>
Forgot this part but I guess it was kind of obvious: :)
DESCRIPTION
The memcpy() function copies n bytes from memory area src to
memory area dest. The memory areas must not overlap. Use memmove(3) if
the memory areas do overlap.
> Is it actually the compiler doing some special magic behind the scenes?
>
>>>
>>> lib/netdev-linux.c:6738:41: runtime error: load of misaligned address
>>> 0x51b000008db4 for type 'const struct rpl_rtnl_link_stats64 *',
>>> which requires 8 byte alignment
>>> 0x51b000008db4: note: pointer points here
>>> cc 00 17 00 01 00 00 00 00 00 00 00 01 00 00 00
>>> ^
>>> 0 0xad2d8 in get_stats_via_netlink lib/netdev-linux.c:6738:17
>>> 1 0x9dcce in netdev_linux_get_stats lib/netdev-linux.c:2293:13
>>> 2 0xee5b8 in netdev_get_stats lib/netdev.c:1722:16
>>> 3 0xc07ad in iface_refresh_stats vswitchd/bridge.c:2795:5
>>> 4 0xbf4fc in iface_create vswitchd/bridge.c:2274:5
>>> 5 0xbf4fc in bridge_add_ports__ vswitchd/bridge.c:1225:21
>>> 6 0x989fc in bridge_add_ports vswitchd/bridge.c:1236:5
>>> 7 0x989fc in bridge_reconfigure vswitchd/bridge.c:952:9
>>> 8 0x9102a in bridge_run vswitchd/bridge.c:3439:9
>>> 9 0xc8976 in main vswitchd/ovs-vswitchd.c:137:9
>>> 10 0x2a1c9 in __libc_start_call_main
>>> 11 0x2a28a in __libc_start_main
>>> 12 0xb3ff4 in _start (vswitchd/ovs-vswitchd+0x734ff4)
>>>
>>> Reported by Clang 18 with UBsan on Ubuntu 24.04.
>>>
>>> Fixes: c8c49a9db9f2 ("netdev-linux: Properly access 32-bit aligned
>>> rtnl_link_stats64 structs.")
>>> Signed-off-by: Ilya Maximets <[email protected]>
>>
>> Reviewed-by: Simon Horman <[email protected]>
>>
>
> Regards,
> Dumitru
>
>
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