[PATCH] powerpc: Fix __clear_user() with KUAP enabled

[Andrew Donnellan]

On 9/12/19 10:50 pm, Christophe Leroy wrote:
>> -extern unsigned long __clear_user(void __user *addr, unsigned long 
>> size);
>> +extern unsigned long clear_user_asm(void __user *addr, unsigned long 
>> size);
>>   static inline unsigned long clear_user(void __user *addr, unsigned 
>> long size)
>>   {
>> @@ -409,12 +409,17 @@ static inline unsigned long clear_user(void 
>> __user *addr, unsigned long size)
>>       might_fault();
>>       if (likely(access_ok(addr, size))) {
>>           allow_write_to_user(addr, size);
>> -        ret = __clear_user(addr, size);
>> +        ret = clear_user_asm(addr, size);
>>           prevent_write_to_user(addr, size);
>>       }
> 
> What about changing the above by the following ?
> 
>         if (likely(access_ok(addr, size)))        ret = 
> __clear_user(addr, size);
> 
>>       return ret;
>>   }
>> +static inline unsigned long __clear_user(void __user *addr, unsigned 
>> long size)
>> +{
>> +        return clear_user(addr, size);
>> +}
>> +
> 
> Then
> 
> static inline unsigned long __clear_user(void __user *addr, unsigned 
> long size)
> {
>      allow_write_to_user(addr, size);
>      ret = clear_user_asm(addr, size);
>      prevent_write_to_user(addr, size);
> 
>      return ret;
> }

This is exactly the patch I initially wrote, I ran it past mpe privately 
and he suggested aliasing clear_user() -> __clear_user() instead, as 
there's not much point keeping a separate path around for a single user 
for a basically non-existent performance gain.

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd at linux.ibm.com             IBM Australia Limited