Re: [PATCH v3 1/8] powerpc/uaccess: Add unsafe_copy_from_user

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 17/01/2021 à 18:19, Christopher M. Riedl a écrit :
> On Mon Jan 11, 2021 at 7:22 AM CST, Christophe Leroy wrote:
>>
>>
>> Le 09/01/2021 à 04:25, Christopher M. Riedl a écrit :
>>> Implement raw_copy_from_user_allowed() which assumes that userspace read
>>> access is open. Use this new function to implement raw_copy_from_user().
>>> Finally, wrap the new function to follow the usual "unsafe_" convention
>>> of taking a label argument.
>>
>> I think there is no point implementing raw_copy_from_user_allowed(), see
>> https://github.com/linuxppc/linux/commit/4b842e4e25b1 and
>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/8c74fc9ce8131cabb10b3e95dc0e430f396ee83e.1610369143.git.christophe.leroy@csgroup.eu/
>>
>> You should simply do:
>>
>> #define unsafe_copy_from_user(d, s, l, e) \
>> unsafe_op_wrap(__copy_tofrom_user((__force void __user *)d, s, l), e)
>>
> 
> I gave this a try and the signal ops decreased by ~8K. Now, to be
> honest, I am not sure what an "acceptable" benchmark number here
> actually is - so maybe this is ok? Same loss with both radix and hash:

I don't think this is ok, but it probably means that you are using unsafe_copy_from_user() to copy 
small constant size data that should be copied with unsafe_get_user() instead.

> 
> 	|                                      | hash   | radix  |
> 	| ------------------------------------ | ------ | ------ |
> 	| linuxppc/next                        | 118693 | 133296 |
> 	| linuxppc/next w/o KUAP+KUEP          | 228911 | 228654 |
> 	| unsafe-signal64                      | 200480 | 234067 |
> 	| unsafe-signal64 (__copy_tofrom_user) | 192467 | 225119 |
> 
> To put this into perspective, prior to KUAP and uaccess flush, signal
> performance in this benchmark was ~290K on hash.
> 
>>
>> Christophe
>>
>>>
>>> The new raw_copy_from_user_allowed() calls non-inline __copy_tofrom_user()
>>> internally. This is still safe to call inside user access blocks formed
>>> with user_*_access_begin()/user_*_access_end() since asm functions are not
>>> instrumented for tracing.
>>>
>>> Signed-off-by: Christopher M. Riedl <cmr@codefail.de>
>>> ---
>>>    arch/powerpc/include/asm/uaccess.h | 28 +++++++++++++++++++---------
>>>    1 file changed, 19 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
>>> index 501c9a79038c..698f3a6d6ae5 100644
>>> --- a/arch/powerpc/include/asm/uaccess.h
>>> +++ b/arch/powerpc/include/asm/uaccess.h
>>> @@ -403,38 +403,45 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
>>>    }
>>>    #endif /* __powerpc64__ */
>>>    
>>> -static inline unsigned long raw_copy_from_user(void *to,
>>> -		const void __user *from, unsigned long n)
>>> +static inline unsigned long
>>> +raw_copy_from_user_allowed(void *to, const void __user *from, unsigned long n)
>>>    {
>>> -	unsigned long ret;
>>>    	if (__builtin_constant_p(n) && (n <= 8)) {
>>> -		ret = 1;
>>> +		unsigned long ret = 1;
>>>    
>>>    		switch (n) {
>>>    		case 1:
>>>    			barrier_nospec();
>>> -			__get_user_size(*(u8 *)to, from, 1, ret);
>>> +			__get_user_size_allowed(*(u8 *)to, from, 1, ret);
>>>    			break;
>>>    		case 2:
>>>    			barrier_nospec();
>>> -			__get_user_size(*(u16 *)to, from, 2, ret);
>>> +			__get_user_size_allowed(*(u16 *)to, from, 2, ret);
>>>    			break;
>>>    		case 4:
>>>    			barrier_nospec();
>>> -			__get_user_size(*(u32 *)to, from, 4, ret);
>>> +			__get_user_size_allowed(*(u32 *)to, from, 4, ret);
>>>    			break;
>>>    		case 8:
>>>    			barrier_nospec();
>>> -			__get_user_size(*(u64 *)to, from, 8, ret);
>>> +			__get_user_size_allowed(*(u64 *)to, from, 8, ret);
>>>    			break;
>>>    		}
>>>    		if (ret == 0)
>>>    			return 0;
>>>    	}
>>>    
>>> +	return __copy_tofrom_user((__force void __user *)to, from, n);
>>> +}
>>> +
>>> +static inline unsigned long
>>> +raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>>> +{
>>> +	unsigned long ret;
>>> +
>>>    	barrier_nospec();
>>>    	allow_read_from_user(from, n);
>>> -	ret = __copy_tofrom_user((__force void __user *)to, from, n);
>>> +	ret = raw_copy_from_user_allowed(to, from, n);
>>>    	prevent_read_from_user(from, n);
>>>    	return ret;
>>>    }
>>> @@ -542,6 +549,9 @@ user_write_access_begin(const void __user *ptr, size_t len)
>>>    #define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
>>>    #define unsafe_put_user(x, p, e) __put_user_goto(x, p, e)
>>>    
>>> +#define unsafe_copy_from_user(d, s, l, e) \
>>> +	unsafe_op_wrap(raw_copy_from_user_allowed(d, s, l), e)
>>> +
>>>    #define unsafe_copy_to_user(d, s, l, e) \
>>>    do {									\
>>>    	u8 __user *_dst = (u8 __user *)(d);				\
>>>