This is a note to let you know that I've just added the patch titled
can: uapi: can.h: mark union inside struct can_frame packed
to the 5.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
can-uapi-can.h-mark-union-inside-struct-can_frame-pa.patch
and it can be found in the queue-5.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 0084115277906a63aa1a04266be996b4fcd78c91
Author: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Date: Mon Mar 22 10:44:54 2021 +0100
can: uapi: can.h: mark union inside struct can_frame packed
[ Upstream commit f5076c6ba02e8e24c61c40bbf48078929bc0fc79 ]
In commit ea7800565a12 ("can: add optional DLC element to Classical
CAN frame structure") the struct can_frame::can_dlc was put into an
anonymous union with another u8 variable.
For various reasons some members in struct can_frame and canfd_frame
including the first 8 byes of data are expected to have the same
memory layout. This is enforced by a BUILD_BUG_ON check in af_can.c.
Since the above mentioned commit this check fails on ARM kernels
compiled with the ARM OABI (which means CONFIG_AEABI not set). In this
case -mabi=apcs-gnu is passed to the compiler, which leads to a
structure size boundary of 32, instead of 8 compared to CONFIG_AEABI
enabled. This means the the union in struct can_frame takes 4 bytes
instead of the expected 1.
Rong Chen illustrates the problem with pahole in the ARM OABI case:
| struct can_frame {
| canid_t can_id; /* 0 4 */
| union {
| __u8 len; /* 4 1 */
| __u8 can_dlc; /* 4 1 */
| }; /* 4 4 */
| __u8 __pad; /* 8 1 */
| __u8 __res0; /* 9 1 */
| __u8 len8_dlc; /* 10 1 */
|
| /* XXX 5 bytes hole, try to pack */
|
| __u8 data[8]
| __attribute__((__aligned__(8))); /* 16 8 */
|
| /* size: 24, cachelines: 1, members: 6 */
| /* sum members: 19, holes: 1, sum holes: 5 */
| /* forced alignments: 1, forced holes: 1, sum forced holes: 5 */
| /* last cacheline: 24 bytes */
| } __attribute__((__aligned__(8)));
Marking the anonymous union as __attribute__((packed)) fixes the
BUILD_BUG_ON problem on these compilers.
Fixes: ea7800565a12 ("can: add optional DLC element to Classical CAN frame structure")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Suggested-by: Rong Chen <rong.a.chen@xxxxxxxxx>
Link: https://lore.kernel.org/linux-can/2c82ec23-3551-61b5-1bd8-178c3407ee83@xxxxxxxxxxxx/
Link: https://lore.kernel.org/r/20210325125850.1620-3-socketcan@xxxxxxxxxxxx
Signed-off-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/uapi/linux/can.h b/include/uapi/linux/can.h
index f75238ac6dce..c7535352fef6 100644
--- a/include/uapi/linux/can.h
+++ b/include/uapi/linux/can.h
@@ -113,7 +113,7 @@ struct can_frame {
*/
__u8 len;
__u8 can_dlc; /* deprecated */
- };
+ } __attribute__((packed)); /* disable padding added in some ABIs */
__u8 __pad; /* padding */
__u8 __res0; /* reserved / padding */
__u8 len8_dlc; /* optional DLC for 8 byte payload length (9 .. 15) */
