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

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Date:	Mon, 12 Nov 2012 10:46:01 +0000
From:	Will Deacon <will.deacon@....com>
To:	Rob Clark <rob.clark@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Arnd Bergmann <arnd@...db.de>,
	"patches@...aro.org" <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Rob Clark <rob@...com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>
Subject: Re: [PATCH] ARM: add get_user() support for 8 byte types

On Fri, Nov 09, 2012 at 09:17:33PM +0000, Rob Clark wrote:
> From: Rob Clark <rob@...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@...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

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