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Message-ID: <54AA5CEE.9050205@imgtec.com>
Date: Mon, 5 Jan 2015 09:44:14 +0000
From: James Hogan <james.hogan@...tec.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
<linux-arch@...r.kernel.org>, <linux-metag@...r.kernel.org>
Subject: Re: [PATCH repost 09/16] metag/uaccess: fix sparse errors
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@...hat.com>
>>> ---
>>> 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@...tec.com>
>>
>> Cheers
>> James
>>
>
>
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