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

[Christophe Leroy]

Le 15/10/2020 à 17:01, 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. The new raw_copy_from_user_allowed() calls
> __copy_tofrom_user() internally, but this is still safe to call in user
> access blocks formed with user_*_access_begin()/user_*_access_end()
> since asm functions are not instrumented for tracing.

Would objtool accept that if it was implemented on powerpc ?

__copy_tofrom_user() is a function which is optimised for larger memory copies (using dcbz, etc ...)
Do we need such an optimisation for unsafe_copy_from_user() ? Or can we do a simple loop as done for 
unsafe_copy_to_user() instead ?

Christophe

> 
> Signed-off-by: Christopher M. Riedl <cmr at 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 26781b044932..66940b4eb692 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -418,38 +418,45 @@ 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;
>   }
> @@ -571,6 +578,9 @@ 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);				\
>