[PATCHv3 11/17] arm64: uaccess: refactor __{get,put}_user

[Robin Murphy]

On 2020-10-26 13:31, Mark Rutland wrote:
> As a step towards implementing __{get,put}_kernel_nofault(), this patch
> splits most user-memory specific logic out of __{get,put}_user(), with
> the memory access and fault handling in new __{raw_get,put}_mem()
> helpers.
> 
> For now the LDR/LDTR patching is left within the *get_mem() helpers, and
> will be removed in a subsequent patch.
> 
> There should be no functional change as a result of this patch.
> 
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: James Morse <james.morse at arm.com>
> Cc: Will Deacon <will at kernel.org>
> ---
>   arch/arm64/include/asm/uaccess.h | 40 +++++++++++++++++++++++++---------------
>   1 file changed, 25 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index d6a4e496ebc64..4ad2990241d78 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -253,7 +253,7 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
>    * The "__xxx_error" versions set the third argument to -EFAULT if an error
>    * occurs, and leave it unchanged on success.
>    */
> -#define __get_user_asm(instr, alt_instr, reg, x, addr, err, feature)	\
> +#define __get_mem_asm(instr, alt_instr, reg, x, addr, err, feature)	\
>   	asm volatile(							\
>   	"1:"ALTERNATIVE(instr "     " reg "1, [%2]\n",			\
>   			alt_instr " " reg "1, [%2]\n", feature)		\
> @@ -268,35 +268,40 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
>   	: "+r" (err), "=&r" (x)						\
>   	: "r" (addr), "i" (-EFAULT))
>   
> -#define __raw_get_user(x, ptr, err)					\
> +#define __raw_get_mem(x, ptr, err)					\
>   do {									\
>   	unsigned long __gu_val;						\
>   	__chk_user_ptr(ptr);						\

Should this move out as well? It seems logical that wherever we figure 
out whether a pointer is "kernel" or "user" in order to call the 
appropriate low-level routine, the __user annotation could be dropped 
from the "kernel" path at that point - or have I misunderstood?

Robin.

> -	uaccess_enable_not_uao();					\
>   	switch (sizeof(*(ptr))) {					\
>   	case 1:								\
> -		__get_user_asm("ldrb", "ldtrb", "%w", __gu_val, (ptr),  \
> +		__get_mem_asm("ldrb", "ldtrb", "%w", __gu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	case 2:								\
> -		__get_user_asm("ldrh", "ldtrh", "%w", __gu_val, (ptr),  \
> +		__get_mem_asm("ldrh", "ldtrh", "%w", __gu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	case 4:								\
> -		__get_user_asm("ldr", "ldtr", "%w", __gu_val, (ptr),	\
> +		__get_mem_asm("ldr", "ldtr", "%w", __gu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	case 8:								\
> -		__get_user_asm("ldr", "ldtr", "%x",  __gu_val, (ptr),	\
> +		__get_mem_asm("ldr", "ldtr", "%x",  __gu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	default:							\
>   		BUILD_BUG();						\
>   	}								\
> -	uaccess_disable_not_uao();					\
>   	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
>   } while (0)
>   
> +#define __raw_get_user(x, ptr, err)					\
> +do {									\
> +	uaccess_enable_not_uao();					\
> +	__raw_get_mem(x, ptr, err);					\
> +	uaccess_disable_not_uao();					\
> +} while (0)
> +
>   #define __get_user_error(x, ptr, err)					\
>   do {									\
>   	__typeof__(*(ptr)) __user *__p = (ptr);				\
> @@ -318,7 +323,7 @@ do {									\
>   
>   #define get_user	__get_user
>   
> -#define __put_user_asm(instr, alt_instr, reg, x, addr, err, feature)	\
> +#define __put_mem_asm(instr, alt_instr, reg, x, addr, err, feature)	\
>   	asm volatile(							\
>   	"1:"ALTERNATIVE(instr "     " reg "1, [%2]\n",			\
>   			alt_instr " " reg "1, [%2]\n", feature)		\
> @@ -332,31 +337,36 @@ do {									\
>   	: "+r" (err)							\
>   	: "r" (x), "r" (addr), "i" (-EFAULT))
>   
> -#define __raw_put_user(x, ptr, err)					\
> +#define __raw_put_mem(x, ptr, err)					\
>   do {									\
>   	__typeof__(*(ptr)) __pu_val = (x);				\
>   	__chk_user_ptr(ptr);						\
> -	uaccess_enable_not_uao();					\
>   	switch (sizeof(*(ptr))) {					\
>   	case 1:								\
> -		__put_user_asm("strb", "sttrb", "%w", __pu_val, (ptr),	\
> +		__put_mem_asm("strb", "sttrb", "%w", __pu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	case 2:								\
> -		__put_user_asm("strh", "sttrh", "%w", __pu_val, (ptr),	\
> +		__put_mem_asm("strh", "sttrh", "%w", __pu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	case 4:								\
> -		__put_user_asm("str", "sttr", "%w", __pu_val, (ptr),	\
> +		__put_mem_asm("str", "sttr", "%w", __pu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	case 8:								\
> -		__put_user_asm("str", "sttr", "%x", __pu_val, (ptr),	\
> +		__put_mem_asm("str", "sttr", "%x", __pu_val, (ptr),	\
>   			       (err), ARM64_HAS_UAO);			\
>   		break;							\
>   	default:							\
>   		BUILD_BUG();						\
>   	}								\
> +} while (0)
> +
> +#define __raw_put_user(x, ptr, err)					\
> +do {									\
> +	uaccess_enable_not_uao();					\
> +	__raw_put_mem(x, ptr, err);					\
>   	uaccess_disable_not_uao();					\
>   } while (0)
>   
>