Re: [PATCH] ARM: add get_user() support for 8 byte types

Will Deacon
2012-11-12T10:46:08Z

On Fri, Nov 09, 2012 at 09:17:33PM +0000, Rob Clark wrote:
> From: Rob Clark <rob@ti.com>
>
> A new atomic modeset/pageflip ioctl being developed in DRM requires
> get_user() to work for 64bit types (in addition to just put_user()).
>
> Signed-off-by: Rob Clark <rob@ti.com>
> ---
> arch/arm/include/asm/uaccess.h | 25 ++++++++++++++++++++-----
> arch/arm/lib/getuser.S | 17 ++++++++++++++++-
> 2 files changed, 36 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
> index 7e1f760..2e3fdb2 100644
> --- a/arch/arm/include/asm/uaccess.h
> +++ b/arch/arm/include/asm/uaccess.h
> @@ -100,6 +100,7 @@ static inline void set_fs(mm_segment_t fs)
> extern int __get_user_1(void *);
> extern int __get_user_2(void *);
> extern int __get_user_4(void *);
> +extern int __get_user_8(void *);
>
> #define __GUP_CLOBBER_1 "lr", "cc"
> #ifdef CONFIG_CPU_USE_DOMAINS
> @@ -108,6 +109,7 @@ extern int __get_user_4(void *);
> #define __GUP_CLOBBER_2 "lr", "cc"
> #endif
> #define __GUP_CLOBBER_4 "lr", "cc"
> +#define __GUP_CLOBBER_8 "lr", "cc"
>
> #define __get_user_x(__r2,__p,__e,__l,__s) \
> __asm__ __volatile__ ( \
> @@ -122,22 +124,35 @@ extern int __get_user_4(void *);
> ({ \
> unsigned long __limit = current_thread_info()->addr_limit - 1; \
> register const typeof(*(p)) __user *__p asm("r0") = (p);\
> - register unsigned long __r2 asm("r2"); \
> register unsigned long __l asm("r1") = __limit; \
> register int __e asm("r0"); \
> switch (sizeof(*(__p))) { \
> - case 1: \
> + case 1: { \
> + register unsigned long __r2 asm("r2"); \
> __get_user_x(__r2, __p, __e, __l, 1); \
> + x = (typeof(*(p))) __r2; \
> break; \
> - case 2: \
> + } \
> + case 2: { \
> + register unsigned long __r2 asm("r2"); \
> __get_user_x(__r2, __p, __e, __l, 2); \
> + x = (typeof(*(p))) __r2; \
> break; \
> - case 4: \
> + } \
> + case 4: { \
> + register unsigned long __r2 asm("r2"); \
> __get_user_x(__r2, __p, __e, __l, 4); \
> + x = (typeof(*(p))) __r2; \
> + break; \
> + } \
> + case 8: { \
> + register unsigned long long __r2 asm("r2"); \

Does this matter? For EABI, we'll pass in (r2, r3) and it's all handcrafted
asm, so the compiler shouldn't care much. For OABI, I think you may have to
do some more work to get the two words where you want them.

> + __get_user_x(__r2, __p, __e, __l, 8); \
> + x = (typeof(*(p))) __r2; \
> break; \
> + } \
> default: __e = __get_user_bad(); break; \
> } \
> - x = (typeof(*(p))) __r2; \
> __e; \
> })
>
> diff --git a/arch/arm/lib/getuser.S b/arch/arm/lib/getuser.S
> index 9b06bb4..d05285c 100644
> --- a/arch/arm/lib/getuser.S
> +++ b/arch/arm/lib/getuser.S
> @@ -18,7 +18,7 @@
> * Inputs: r0 contains the address
> * r1 contains the address limit, which must be preserved
> * Outputs: r0 is the error code
> - * r2 contains the zero-extended value
> + * r2, r3 contains the zero-extended value
> * lr corrupted
> *
> * No other registers must be altered. (see <asm/uaccess.h>
> @@ -66,6 +66,19 @@ ENTRY(__get_user_4)
> mov pc, lr
> ENDPROC(__get_user_4)
>
> +ENTRY(__get_user_8)
> + check_uaccess r0, 4, r1, r2, __get_user_bad

Shouldn't you be passing 8 here, so that we validate the correct range?

> +#ifdef CONFIG_THUMB2_KERNEL
> +5: TUSER(ldr) r2, [r0]
> +6: TUSER(ldr) r3, [r0, #4]
> +#else
> +5: TUSER(ldr) r2, [r0], #4
> +6: TUSER(ldr) r3, [r0]
> +#endif

This doesn't work for EABI big-endian systems.

Will