[PATCH] Revert "arm64: uaccess: implement unsafe accessors"

[julien.thierry@arm.com (Julien Thierry)]

On 10/10/18 16:55, James Morse wrote:
> This reverts commit a1f33941f7e103bcf471eaf8461b212223c642d6.
> 
> The unsafe accessors allow the PAN enable/disable calls to be made
> once for a group of accesses. Adding these means we can now have
> sequences that look like this:
> 
> | user_access_begin();
> | unsafe_put_user(static-value, x, err);
> | unsafe_put_user(helper-that-sleeps(), x, err);
> | user_access_end();
> 
> Calling schedule() without taking an exception doesn't switch the
> PSTATE or TTBRs. We can switch out of a uaccess-enabled region, and
> run other code with uaccess enabled for a different thread.
> 
> We can also switch from uaccess-disabled code back into this region,
> meaning the unsafe_put_user()s will fault.
> 
> For software-PAN, threads that do this will get stuck as
> handle_mm_fault() will determine the page has already been mapped in,
> but we fault again as the page tables aren't loaded.
> 
> To solve this we need code in __switch_to() that save/restores the
> PAN state.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> CC: Julien Thierry <julien.thierry@arm.com>
> Acked-by: Mark Rutland <mark.rutland@arm.com>

Acked-by: Julien Thierry <julien.thierry@arm.com>

> ---
> This reverts a patch queued in for-next/core.
> 
>   arch/arm64/include/asm/uaccess.h | 61 ++++++++------------------------
>   1 file changed, 15 insertions(+), 46 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 8ac6e34922e7..07c34087bd5e 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -276,9 +276,11 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
>   	: "+r" (err), "=&r" (x)						\
>   	: "r" (addr), "i" (-EFAULT))
>   
> -#define __get_user_err_unsafe(x, ptr, err)				\
> +#define __get_user_err(x, ptr, err)					\
>   do {									\
>   	unsigned long __gu_val;						\
> +	__chk_user_ptr(ptr);						\
> +	uaccess_enable_not_uao();					\
>   	switch (sizeof(*(ptr))) {					\
>   	case 1:								\
>   		__get_user_asm("ldrb", "ldtrb", "%w", __gu_val, (ptr),  \
> @@ -299,24 +301,17 @@ do {									\
>   	default:							\
>   		BUILD_BUG();						\
>   	}								\
> -	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
> -} while (0)
> -
> -#define __get_user_err_check(x, ptr, err)				\
> -do {									\
> -	__chk_user_ptr(ptr);						\
> -	uaccess_enable_not_uao();					\
> -	__get_user_err_unsafe((x), (ptr), (err));			\
>   	uaccess_disable_not_uao();					\
> +	(x) = (__force __typeof__(*(ptr)))__gu_val;			\
>   } while (0)
>   
> -#define __get_user_err(x, ptr, err, accessor)				\
> +#define __get_user_check(x, ptr, err)					\
>   ({									\
>   	__typeof__(*(ptr)) __user *__p = (ptr);				\
>   	might_fault();							\
>   	if (access_ok(VERIFY_READ, __p, sizeof(*__p))) {		\
>   		__p = uaccess_mask_ptr(__p);				\
> -		accessor((x), __p, (err));				\
> +		__get_user_err((x), __p, (err));			\
>   	} else {							\
>   		(x) = 0; (err) = -EFAULT;				\
>   	}								\
> @@ -324,14 +319,14 @@ do {									\
>   
>   #define __get_user_error(x, ptr, err)					\
>   ({									\
> -	__get_user_err((x), (ptr), (err), __get_user_err_check);	\
> +	__get_user_check((x), (ptr), (err));				\
>   	(void)0;							\
>   })
>   
>   #define __get_user(x, ptr)						\
>   ({									\
>   	int __gu_err = 0;						\
> -	__get_user_err((x), (ptr), __gu_err, __get_user_err_check);	\
> +	__get_user_check((x), (ptr), __gu_err);				\
>   	__gu_err;							\
>   })
>   
> @@ -351,9 +346,11 @@ do {									\
>   	: "+r" (err)							\
>   	: "r" (x), "r" (addr), "i" (-EFAULT))
>   
> -#define __put_user_err_unsafe(x, ptr, err)				\
> +#define __put_user_err(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),	\
> @@ -374,24 +371,16 @@ do {									\
>   	default:							\
>   		BUILD_BUG();						\
>   	}								\
> -} while (0)
> -
> -
> -#define __put_user_err_check(x, ptr, err)				\
> -do {									\
> -	__chk_user_ptr(ptr);						\
> -	uaccess_enable_not_uao();					\
> -	__put_user_err_unsafe((x), (ptr), (err));			\
>   	uaccess_disable_not_uao();					\
>   } while (0)
>   
> -#define __put_user_err(x, ptr, err, accessor)				\
> +#define __put_user_check(x, ptr, err)					\
>   ({									\
>   	__typeof__(*(ptr)) __user *__p = (ptr);				\
>   	might_fault();							\
>   	if (access_ok(VERIFY_WRITE, __p, sizeof(*__p))) {		\
>   		__p = uaccess_mask_ptr(__p);				\
> -		accessor((x), __p, (err));				\
> +		__put_user_err((x), __p, (err));			\
>   	} else	{							\
>   		(err) = -EFAULT;					\
>   	}								\
> @@ -399,39 +388,19 @@ do {									\
>   
>   #define __put_user_error(x, ptr, err)					\
>   ({									\
> -	__put_user_err((x), (ptr), (err), __put_user_err_check);	\
> +	__put_user_check((x), (ptr), (err));				\
>   	(void)0;							\
>   })
>   
>   #define __put_user(x, ptr)						\
>   ({									\
>   	int __pu_err = 0;						\
> -	__put_user_err((x), (ptr), __pu_err, __put_user_err_check);	\
> +	__put_user_check((x), (ptr), __pu_err);				\
>   	__pu_err;							\
>   })
>   
>   #define put_user	__put_user
>   
> -
> -#define user_access_begin()	uaccess_enable_not_uao()
> -#define user_access_end()	uaccess_disable_not_uao()
> -
> -#define unsafe_get_user(x, ptr, err)					\
> -do {									\
> -	int __gu_err = 0;						\
> -	__get_user_err((x), (ptr), __gu_err, __get_user_err_unsafe);	\
> -	if (__gu_err != 0)						\
> -		goto err;						\
> -} while (0)
> -
> -#define unsafe_put_user(x, ptr, err)					\
> -do {									\
> -	int __pu_err = 0;						\
> -	__put_user_err((x), (ptr), __pu_err, __put_user_err_unsafe);	\
> -	if (__pu_err != 0)						\
> -		goto err;						\
> -} while (0)
> -
>   extern unsigned long __must_check __arch_copy_from_user(void *to, const void __user *from, unsigned long n);
>   #define raw_copy_from_user(to, from, n)					\
>   ({									\
> 

-- 
Julien Thierry