Re: [PATCH v3 2/2] m68k: improve __constant_copy_to_user_asm() fault handling

[Finn Thain <fthain@linux-m68k.org>]

On Sat, 27 Apr 2024, Michael Schmitz wrote:

> A problem similar to that reported for __put_user_asm and
> __generic_copy_to_user is also present in
> __constant_copy_to_user_asm.
> 
> Address the problem by extending the exception table to cover
> two instructions past each moves instruction, and adding a
> single NOP at the very end to catch faults on the final
> instruction (which is not guaranteed to be a movesb!).
> 
> Tested on 68030 (Atari Falcon 030) with a transfer beginning
> at a single byte at the end of a mapped page followed by
> seven more bytes on an unmapped page (testcase derived from
> stress-ng sysbadaddr stressor by Finn Thain and modified to
> use the llseek syscall).
> 
> Cc: Finn Thain <fthain@linux-m68k.org>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Link: https://lore.kernel.org/all/e0f23460779e6d16e2633486ac4841790ef2aca0.1713176294.git.fthain@linux-m68k.org
> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>

Tested-by: Finn Thain <fthain@linux-m68k.org>

> ---
>  arch/m68k/include/asm/uaccess.h | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/m68k/include/asm/uaccess.h b/arch/m68k/include/asm/uaccess.h
> index 44e52d8323e5..f1f4b62d6f69 100644
> --- a/arch/m68k/include/asm/uaccess.h
> +++ b/arch/m68k/include/asm/uaccess.h
> @@ -288,10 +288,11 @@ __constant_copy_from_user(void *to, const void __user *from, unsigned long n)
>  		"21:	"MOVES"."#s2"	%3,(%1)+\n"			\
>  		"22:\n"							\
>  		"	.ifnc	\""#s3"\",\"\"\n"			\
> -		"	move."#s3"	(%2)+,%3\n"			\
> -		"31:	"MOVES"."#s3"	%3,(%1)+\n"			\
> -		"32:\n"							\
> +		"31:	move."#s3"	(%2)+,%3\n"			\
> +		"32:	"MOVES"."#s3"	%3,(%1)+\n"			\
> +		"33:\n"							\
>  		"	.endif\n"					\
> +		"34:	nop\n"						\
>  		"4:\n"							\
>  		"\n"							\
>  		"	.section __ex_table,\"a\"\n"			\
> @@ -303,7 +304,9 @@ __constant_copy_from_user(void *to, const void __user *from, unsigned long n)
>  		"	.ifnc	\""#s3"\",\"\"\n"			\
>  		"	.long	31b,5f\n"				\
>  		"	.long	32b,5f\n"				\
> +		"	.long	33b,5f\n"				\
>  		"	.endif\n"					\
> +		"	.long	34b,5f\n"				\
>  		"	.previous\n"					\
>  		"\n"							\
>  		"	.section .fixup,\"ax\"\n"			\
>