[PATCH v3] ubsan: don't handle misaligned address when support unaligned access

[Ding Tianhong]

The ubsan always report Warning just like:

UBSAN: Undefined behaviour in ../include/linux/etherdevice.h:386:9
load of misaligned address ffffffc069ba0482 for type 'long unsigned int'
which requires 8 byte alignment
CPU: 0 PID: 901 Comm: sshd Not tainted 4.xx+ #1
Hardware name: linux,dummy-virt (DT)
Call trace:
[<ffffffc000093600>] dump_backtrace+0x0/0x348
[<ffffffc000093968>] show_stack+0x20/0x30
[<ffffffc001651664>] dump_stack+0x144/0x1b4
[<ffffffc0016519b0>] ubsan_epilogue+0x18/0x74
[<ffffffc001651bac>] __ubsan_handle_type_mismatch+0x1a0/0x25c
[<ffffffc00125d8a0>] dev_gro_receive+0x17d8/0x1830
[<ffffffc00125d928>] napi_gro_receive+0x30/0x158
[<ffffffc000f4f93c>] virtnet_receive+0xad4/0x1fa8

The reason is that when enable the CONFIG_UBSAN_ALIGNMENT, the ubsan
will report the unaligned access even if the system support it
(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y), it will produce a lot
of noise in the log and cause confusion.

This patch will close the detection of unaligned access when
the system support unaligned access.

Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx>
---
 lib/ubsan.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/ubsan.c b/lib/ubsan.c
index fb0409d..0799678 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -321,9 +321,10 @@ void __ubsan_handle_type_mismatch(struct type_mismatch_data *data,

 	if (!ptr)
 		handle_null_ptr_deref(data);
-	else if (data->alignment && !IS_ALIGNED(ptr, data->alignment))
-		handle_missaligned_access(data, ptr);
-	else
+	else if (data->alignment && !IS_ALIGNED(ptr, data->alignment)) {
+		if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
+			handle_missaligned_access(data, ptr);
+	} else
 		handle_object_size_mismatch(data, ptr);
 }
 EXPORT_SYMBOL(__ubsan_handle_type_mismatch);
-- 
1.8.3.1