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

[PATCH] 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@huawei.com>
---
 lib/ubsan.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/ubsan.c b/lib/ubsan.c
index fb0409d..278b4c3 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -321,7 +321,8 @@ 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))
+	else if (data->alignment && !IS_ALIGNED(ptr, data->alignment) &&
+		 !IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
 		handle_missaligned_access(data, ptr);
 	else
 		handle_object_size_mismatch(data, ptr);
-- 
1.8.3.1

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

[David Laight]

From: Ding Tianhong
> Sent: 01 December 2017 11:32
> To: akpm@linux-foundation.org; aryabinin@virtuozzo.co; linux-kernel@vger.kernel.org; LinuxArm
> Subject: [PATCH] ubsan: don't handle misaligned address when support unaligned access
> 
> 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@huawei.com>
> ---
>  lib/ubsan.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/ubsan.c b/lib/ubsan.c
> index fb0409d..278b4c3 100644
> --- a/lib/ubsan.c
> +++ b/lib/ubsan.c
> @@ -321,7 +321,8 @@ 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))
> +	else if (data->alignment && !IS_ALIGNED(ptr, data->alignment) &&
> +		 !IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
>  		handle_missaligned_access(data, ptr);
>  	else
>  		handle_object_size_mismatch(data, ptr);

Won't that report an object size error instead of actually
doing the required access?

Surely it shouldn't get into this function at all?

I guess 'alignment' is set to 4 or 8.
If it were set to 3 or 7 (or 0) then the tests on the pointer
would be much simpler - maybe at a slight extra cost in setup.

	David

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

[Ding Tianhong]

On 2017/12/1 19:47, David Laight wrote:
>> 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@huawei.com>
>> ---
>>  lib/ubsan.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/ubsan.c b/lib/ubsan.c
>> index fb0409d..278b4c3 100644
>> --- a/lib/ubsan.c
>> +++ b/lib/ubsan.c
>> @@ -321,7 +321,8 @@ 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))
>> +	else if (data->alignment && !IS_ALIGNED(ptr, data->alignment) &&
>> +		 !IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
>>  		handle_missaligned_access(data, ptr);
>>  	else
>>  		handle_object_size_mismatch(data, ptr);
> 
> Won't that report an object size error instead of actually
> doing the required access?
>

Yes，I miss it.


> Surely it shouldn't get into this function at all?
> 
> I guess 'alignment' is set to 4 or 8.
> If it were set to 3 or 7 (or 0) then the tests on the pointer
> would be much simpler - maybe at a slight extra cost in setup.
> 

Looks like we need to fix it in the handle_missaligned_access:

diff --git a/lib/ubsan.c b/lib/ubsan.c
index 278b4c3..040f8b2 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -289,6 +289,9 @@ static void handle_missaligned_access(struct type_mismatch_data *data,
        if (suppress_report(&data->location))
                return;

+       if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
+               return;
+
        ubsan_prologue(&data->location, &flags);

        pr_err("%s misaligned address %p for type %s\n",


Thanks
Ding


> 	David
>