Subject: Re: [v4] Fix to avoid IS_ERR_VALUE and IS_ERR abuses on 64bit systems.

From: arvind Yadav <[email-masked]>
Date: Wed, 3 Aug 2016 19:25:16 +0530

On Wednesday 03 August 2016 01:27 AM, Scott Wood wrote:
> On 08/02/2016 10:34 AM, arvind Yadav wrote:
>>
>> On Tuesday 02 August 2016 01:15 PM, Arnd Bergmann wrote:
>>> On Monday, August 1, 2016 4:55:43 PM CEST Scott Wood wrote:
>>>> On 08/01/2016 02:02 AM, Arnd Bergmann wrote:
>>>>>> diff --git a/include/linux/err.h b/include/linux/err.h
>>>>>> index 1e35588..c2a2789 100644
>>>>>> --- a/include/linux/err.h
>>>>>> +++ b/include/linux/err.h
>>>>>> @@ -18,7 +18,17 @@
>>>>>>   
>>>>>>   #ifndef __ASSEMBLY__
>>>>>>   
>>>>>> -#define IS_ERR_VALUE(x) unlikely((unsigned long)(void *)(x) >= (unsigned long)-MAX_ERRNO)
>>>>>> +#define IS_ERR_VALUE(x) unlikely(is_error_check(x))
>>>>>> +
>>>>>> +static inline int is_error_check(unsigned long error)
>>>>> Please leave the existing macro alone. I think you were looking for
>>>>> something specific to the return code of qe_muram_alloc() function,
>>>>> so please add a helper in that subsystem if you need it, not in
>>>>> the generic header files.
>>>> qe_muram_alloc (a.k.a. cpm_muram_alloc) returns unsigned long.  The
>>>> problem is certain callers that store the return value in a u32.  Why
>>>> not just fix those callers to store it in unsigned long (at least until
>>>> error checking is done)?
>>>>
>>> Yes, that would also address another problem with code like
>>>
>>>           kfree((void *)ugeth->tx_bd_ring_offset[i]);
>>>
>>> which is not 64-bit safe when tx_bd_ring_offset is a 32-bit value
>>> that also holds the return value of qe_muram_alloc.
> Well, hopefully it doesn't hold a return of qe_muram_alloc() when it's
> being passed to kfree()...
>
> There's also the code that casts kmalloc()'s return to u32, etc.
> ucc_geth is not 64-bit clean in general.
>
>>> 	Arnd
>> Yes, we will fix caller. Caller api is not safe on 64bit.
> The API is fine (or at least, I haven't seen a valid issue pointed out
> yet).  The problem is the ucc_geth driver.
>
>> Even qe_muram_addr(a.k.a. cpm_muram_addr )passing value unsigned int,
>> but it should be unsigned long.
> cpm_muram_addr takes unsigned long as a parameter, not that it matters
> since you can't pass errors into it and a muram offset should never
> exceed 32 bits.
>
> -Scott
Yes, It will work for 32bit machine. But will not safe for 64bit.

Example :
ugeth->tx_bd_ring_offset[j] =
     qe_muram_alloc(length  UCC_GETH_TX_BD_RING_ALIGNMENT);
if (!IS_ERR_VALUE(ugeth->tx_bd_ring_offset[j]))
    ugeth->p_tx_bd_ring[j] =
    (u8 __iomem *) qe_muram_addr(ugeth-> tx_bd_ring_offset[j]);

If qe_muram_alloc will return any error,  IS_ERR_VALUE will
always return 0 (IS_ERR_VALUE will always pass for 'unsigned int').
Now qe_muram_addr will return wrong virtual address. Which
can cause an error.

-Arvind