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

Robin Murphy
2020-10-27T18:05:38Z

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@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: James Morse <james.morse@arm.com>
> Cc: Will Deacon <will@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)
>
>