Re: [PATCH repost 09/16] metag/uaccess: fix sparse errors

[James Hogan]

On 04/01/15 10:52, Michael S. Tsirkin wrote:
> On Fri, Jan 02, 2015 at 03:41:02PM +0000, James Hogan wrote:
>> Hi,
>>
>> On 25/12/14 09:29, Michael S. Tsirkin wrote:
>>> virtio wants to read bitwise types from userspace using get_user.  At the
>>> moment this triggers sparse errors, since the value is passed through an
>>> integer.
>>>
>>> Fix that up using __force.
>>
>> I still see these sparse warnings with metag even with your patch:
>>
>>   CHECK   drivers/vhost/vhost.c
>> drivers/vhost/vhost.c:1004:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1004:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1004:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1004:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1022:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1022:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1022:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1022:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1373:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1373:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1373:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1373:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1377:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1377:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1377:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1377:21: warning: cast from restricted __virtio32
>> drivers/vhost/vhost.c:1425:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1425:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1425:13: warning: cast from restricted __virtio16
>> drivers/vhost/vhost.c:1425:13: warning: cast from restricted __virtio16
>>
>> Which something like the following hunk fixes in a similar way to yours:
>>
>> diff --git a/arch/metag/include/asm/uaccess.h b/arch/metag/include/asm/uaccess.h
>> index 0748b0a97986..594497053748 100644
>> --- a/arch/metag/include/asm/uaccess.h
>> +++ b/arch/metag/include/asm/uaccess.h
>> @@ -112,13 +112,17 @@ do {                                                            \
>>  	retval = 0;                                             \
>>  	switch (size) {                                         \
>>  	case 1:								\
>> -		retval = __put_user_asm_b((unsigned int)x, ptr); break;	\
>> +		retval = __put_user_asm_b((__force unsigned int)x, ptr); \
>> +		break;							\
>>  	case 2:								\
>> -		retval = __put_user_asm_w((unsigned int)x, ptr); break;	\
>> +		retval = __put_user_asm_w((__force unsigned int)x, ptr); \
>> +		break;							\
>>  	case 4:								\
>> -		retval = __put_user_asm_d((unsigned int)x, ptr); break;	\
>> +		retval = __put_user_asm_d((__force unsigned int)x, ptr); \
>> +		break;							\
>>  	case 8:								\
>> -		retval = __put_user_asm_l((unsigned long long)x, ptr); break; \
>> +		retval = __put_user_asm_l((__force unsigned long long)x, ptr); \
>> +		break;							\
>>  	default:							\
>>  		__put_user_bad();					\
>>  	}	
>>
>> As far as I understand it, using __force on the value (as opposed to the
>> pointer) is safe here, in the sense of not masking any genuine defects.
>> Do you agree? Do you want to apply that hunk with your patch too?
> 
> what about this code:
>              u16 v = 0;
>              int rc = get_user(v, (__force __le16 __user *)p);
> 
> it should trigger a warning, does it?

No, but it didn't previously either, and doesn't seem to with x86_64 either.

I tried __be16 too, since I presume you're referring to a discrepancy
between the native byte order of v (u16) and the foreign byte order of
*p (__be16)?

Cheers
James

> 
> 
> 
>> Note, this change also suppresses warnings for writing a pointer to
>> userland due to the casts to unsigned int / unsigned long long, such as
>> the following (each 4 times due to 4 cases above):
>>
>> kernel/signal.c:2740:25: warning: cast removes address space of expression
>> kernel/signal.c:2747:24: warning: cast removes address space of expression
>> kernel/signal.c:2760:24: warning: cast removes address space of expression
>> kernel/signal.c:2761:24: warning: cast removes address space of expression
>> kernel/signal.c:2775:24: warning: cast removes address space of expression
>> kernel/signal.c:2779:24: warning: cast removes address space of expression
>> kernel/signal.c:3202:25: warning: cast removes address space of expression
>> kernel/signal.c:3225:17: warning: cast removes address space of expression
>> kernel/futex.c:2769:16: warning: cast removes address space of expression
>>
>>>
>>> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>>> ---
>>>  arch/metag/include/asm/uaccess.h | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/metag/include/asm/uaccess.h b/arch/metag/include/asm/uaccess.h
>>> index 0748b0a..c314b45 100644
>>> --- a/arch/metag/include/asm/uaccess.h
>>> +++ b/arch/metag/include/asm/uaccess.h
>>> @@ -135,7 +135,7 @@ extern long __get_user_bad(void);
>>>  ({                                                              \
>>>  	long __gu_err, __gu_val;                                \
>>>  	__get_user_size(__gu_val, (ptr), (size), __gu_err);	\
>>> -	(x) = (__typeof__(*(ptr)))__gu_val;                     \
>>> +	(x) = (__force __typeof__(*(ptr)))__gu_val;                     \
>>
>> Can you adjust the position of the \ to line up please
>>
>>>  	__gu_err;                                               \
>>>  })
>>>  
>>> @@ -145,7 +145,7 @@ extern long __get_user_bad(void);
>>>  	const __typeof__(*(ptr)) __user *__gu_addr = (ptr);		\
>>>  	if (access_ok(VERIFY_READ, __gu_addr, size))			\
>>>  		__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\
>>> -	(x) = (__typeof__(*(ptr)))__gu_val;                             \
>>> +	(x) = (__force __typeof__(*(ptr)))__gu_val;                             \
>>
>> same here (this one causes a checkpatch error due to 80 column limit)
>>
>>>  	__gu_err;                                                       \
>>>  })
>>>  
>>>
>>
>> With those changes,
>> Acked-by: James Hogan <james.hogan@xxxxxxxxxx>
>>
>> Cheers
>> James
>>
> 
>

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