Re: [PATCH 3/3] MIPS: uaccess: Take EVA into account in [__]clear_user

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Hi stable folk,

On Wed, Aug 05, 2015 at 04:41:39PM +0100, James Hogan wrote:
> __clear_user() (and clear_user() which uses it), always access the user
> mode address space, which results in EVA store instructions when EVA is
> enabled even if the current user address limit is KERNEL_DS.
> 
> Fix this by adding a new symbol __bzero_kernel for the normal kernel
> address space bzero in EVA mode, and call that from __clear_user() if
> eva_kernel_access().
> 
> Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Cc: Markos Chandras <markos.chandras@xxxxxxxxxx>
> Cc: Paul Burton <paul.burton@xxxxxxxxxx>
> Cc: Leonid Yegoshin <leonid.yegoshin@xxxxxxxxxx>
> Cc: linux-mips@xxxxxxxxxxxxxx
> ---
> I've not Cc'd stable on this patch as eva_kernel_access() was only added
> in 4.2. I'll submit a backport once it is merged.

This is now merged, but a little later than anticipated. Please can
patch 2 & 3 be applied to stable >= v4.2.

The upstream commits are:

6f06a2c45d8d714ea3b11a360b4a7191e52acaa4
("MIPS: uaccess: Take EVA into account in __copy_from_user()")

d6a428fb583738ad685c91a684748cdee7b2a05f
("MIPS: uaccess: Take EVA into account in [__]clear_user")

As stated above, I'll provide backports for v3.15 <= version < v4.2.

Thanks
James

> ---
>  arch/mips/include/asm/uaccess.h | 32 ++++++++++++++++++++++----------
>  arch/mips/kernel/mips_ksyms.c   |  2 ++
>  arch/mips/lib/memset.S          |  2 ++
>  3 files changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
> index 5014e187df23..2e3b3991cf0b 100644
> --- a/arch/mips/include/asm/uaccess.h
> +++ b/arch/mips/include/asm/uaccess.h
> @@ -1235,16 +1235,28 @@ __clear_user(void __user *addr, __kernel_size_t size)
>  {
>  	__kernel_size_t res;
>  
> -	might_fault();
> -	__asm__ __volatile__(
> -		"move\t$4, %1\n\t"
> -		"move\t$5, $0\n\t"
> -		"move\t$6, %2\n\t"
> -		__MODULE_JAL(__bzero)
> -		"move\t%0, $6"
> -		: "=r" (res)
> -		: "r" (addr), "r" (size)
> -		: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
> +	if (eva_kernel_access()) {
> +		__asm__ __volatile__(
> +			"move\t$4, %1\n\t"
> +			"move\t$5, $0\n\t"
> +			"move\t$6, %2\n\t"
> +			__MODULE_JAL(__bzero_kernel)
> +			"move\t%0, $6"
> +			: "=r" (res)
> +			: "r" (addr), "r" (size)
> +			: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
> +	} else {
> +		might_fault();
> +		__asm__ __volatile__(
> +			"move\t$4, %1\n\t"
> +			"move\t$5, $0\n\t"
> +			"move\t$6, %2\n\t"
> +			__MODULE_JAL(__bzero)
> +			"move\t%0, $6"
> +			: "=r" (res)
> +			: "r" (addr), "r" (size)
> +			: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
> +	}
>  
>  	return res;
>  }
> diff --git a/arch/mips/kernel/mips_ksyms.c b/arch/mips/kernel/mips_ksyms.c
> index 291af0b5c482..e2b6ab74643d 100644
> --- a/arch/mips/kernel/mips_ksyms.c
> +++ b/arch/mips/kernel/mips_ksyms.c
> @@ -17,6 +17,7 @@
>  #include <asm/fpu.h>
>  #include <asm/msa.h>
>  
> +extern void *__bzero_kernel(void *__s, size_t __count);
>  extern void *__bzero(void *__s, size_t __count);
>  extern long __strncpy_from_kernel_nocheck_asm(char *__to,
>  					      const char *__from, long __len);
> @@ -64,6 +65,7 @@ EXPORT_SYMBOL(__copy_from_user_eva);
>  EXPORT_SYMBOL(__copy_in_user_eva);
>  EXPORT_SYMBOL(__copy_to_user_eva);
>  EXPORT_SYMBOL(__copy_user_inatomic_eva);
> +EXPORT_SYMBOL(__bzero_kernel);
>  #endif
>  EXPORT_SYMBOL(__bzero);
>  EXPORT_SYMBOL(__strncpy_from_kernel_nocheck_asm);
> diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S
> index b8e63fd00375..8f0019a2e5c8 100644
> --- a/arch/mips/lib/memset.S
> +++ b/arch/mips/lib/memset.S
> @@ -283,6 +283,8 @@ LEAF(memset)
>  1:
>  #ifndef CONFIG_EVA
>  FEXPORT(__bzero)
> +#else
> +FEXPORT(__bzero_kernel)
>  #endif
>  	__BUILD_BZERO LEGACY_MODE
>  
> -- 
> 2.3.6
> 

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