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Subject: Re: [PATCH v2] ubsan: don't handle misaligned address when support
 unaligned access
To: Andrew Morton <akpm@linux-foundation.org>
References: <5b905d56-609e-3822-096a-3b93b3eb7675@huawei.com>
 <20171206164916.687d5006b7a49ef1149e7154@linux-foundation.org>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        LinuxArm <linuxarm@huawei.com>, David Laight <David.Laight@ACULAB.COM>,
        "Andrey Ryabinin" <aryabinin@virtuozzo.com>
From: Ding Tianhong <dingtianhong@huawei.com>
Message-ID: <b471cb7b-85b0-f02d-1009-df9063b50747@huawei.com>
Date: Thu, 7 Dec 2017 09:11:07 +0800
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Hi Andrew:

Sorry for the mistaken of the Andrey's email.

After the test I found this version still exist the problem that will transfer the align problem to size
mismatch, I will send a new version to fix it.

The correct way is like this:

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);
--


Thanks
Ding

On 2017/12/7 8:49, Andrew Morton wrote:
> (correcting Andrey's email address)
> 
> 
> From: Ding Tianhong <dingtianhong@huawei.com>
> Subject: lib/ubsan.c: don't handle misaligned address when kernel supports unaligned access
> 
> ubsan reports a warning 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 enabling the CONFIG_UBSAN_ALIGNMENT, ubsan will
> report the unaligned access even if the system supports it
> (CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y).  This produces a lot of noise
> in the log and causes confusion.
> 
> Prevent the detection of unaligned access when the system support
> unaligned access.
> 
> Link: http://lkml.kernel.org/r/5b905d56-609e-3822-096a-3b93b3eb7675@huawei.com
> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
> Cc: David Laight <David.Laight@ACULAB.COM>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  lib/ubsan.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff -puN lib/ubsan.c~ubsan-dont-handle-misaligned-address-when-support-unaligned-access lib/ubsan.c
> --- a/lib/ubsan.c~ubsan-dont-handle-misaligned-address-when-support-unaligned-access
> +++ a/lib/ubsan.c
> @@ -322,7 +322,8 @@ void __ubsan_handle_type_mismatch(struct
>  	if (!ptr)
>  		handle_null_ptr_deref(data);
>  	else if (data->alignment && !IS_ALIGNED(ptr, data->alignment))
> -		handle_missaligned_access(data, ptr);
> +		if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
> +			handle_missaligned_access(data, ptr);
>  	else
>  		handle_object_size_mismatch(data, ptr);
>  }
> _
> 
> 
> .
>