Re: [RFC PATCH v1 01/10] s390/uaccess: Add storage key checked access to user memory

[Janosch Frank <frankja@linux.ibm.com>]

On 1/18/22 10:52, Janis Schoetterl-Glausch wrote:
> KVM needs a mechanism to do accesses to guest memory that honor
> storage key protection.
> Since the copy_to/from_user implementation makes use of move
> instructions that support having an additional access key supplied,
> we can implement __copy_from/to_user_with_key by enhancing the
> existing implementation.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>

For this I'd like to have buy-in from the kernel maintainers.
The patch looks good to me but currently I don't understand all of the 
background so:

Acked-by: Janosch Frank <frankja@linux.ibm.com>

> ---
>   arch/s390/include/asm/uaccess.h | 32 ++++++++++++++++++
>   arch/s390/lib/uaccess.c         | 57 +++++++++++++++++++++++----------
>   2 files changed, 72 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
> index 02b467461163..5138040348cc 100644
> --- a/arch/s390/include/asm/uaccess.h
> +++ b/arch/s390/include/asm/uaccess.h
> @@ -33,6 +33,38 @@ static inline int __range_ok(unsigned long addr, unsigned long size)
>   
>   #define access_ok(addr, size) __access_ok(addr, size)
>   
> +unsigned long __must_check
> +raw_copy_from_user_with_key(void *to, const void __user *from, unsigned long n,
> +			    char key);
> +
> +unsigned long __must_check
> +raw_copy_to_user_with_key(void __user *to, const void *from, unsigned long n,
> +			  char key);
> +
> +static __always_inline __must_check unsigned long
> +__copy_from_user_with_key(void *to, const void __user *from, unsigned long n,
> +			  char key)
> +{
> +	might_fault();
> +	if (should_fail_usercopy())
> +		return n;
> +	instrument_copy_from_user(to, from, n);
> +	check_object_size(to, n, false);
> +	return raw_copy_from_user_with_key(to, from, n, key);
> +}
> +
> +static __always_inline __must_check unsigned long
> +__copy_to_user_with_key(void __user *to, const void *from, unsigned long n,
> +			char key)
> +{
> +	might_fault();
> +	if (should_fail_usercopy())
> +		return n;
> +	instrument_copy_to_user(to, from, n);
> +	check_object_size(from, n, true);
> +	return raw_copy_to_user_with_key(to, from, n, key);
> +}
> +
>   unsigned long __must_check
>   raw_copy_from_user(void *to, const void __user *from, unsigned long n);
>   
> diff --git a/arch/s390/lib/uaccess.c b/arch/s390/lib/uaccess.c
> index d3a700385875..ce7a150dd93a 100644
> --- a/arch/s390/lib/uaccess.c
> +++ b/arch/s390/lib/uaccess.c
> @@ -59,11 +59,13 @@ static inline int copy_with_mvcos(void)
>   #endif
>   
>   static inline unsigned long copy_from_user_mvcos(void *x, const void __user *ptr,
> -						 unsigned long size)
> +						 unsigned long size, char key)
>   {
>   	unsigned long tmp1, tmp2;
>   	union oac spec = {
> +		.oac2.key = key,
>   		.oac2.as = PSW_BITS_AS_SECONDARY,
> +		.oac2.k = 1,
>   		.oac2.a = 1,
>   	};
>   
> @@ -94,19 +96,19 @@ static inline unsigned long copy_from_user_mvcos(void *x, const void __user *ptr
>   }
>   
>   static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
> -						unsigned long size)
> +						unsigned long size, char key)
>   {
>   	unsigned long tmp1, tmp2;
>   
>   	tmp1 = -256UL;
>   	asm volatile(
>   		"   sacf  0\n"
> -		"0: mvcp  0(%0,%2),0(%1),%3\n"
> +		"0: mvcp  0(%0,%2),0(%1),%[key]\n"
>   		"7: jz    5f\n"
>   		"1: algr  %0,%3\n"
>   		"   la    %1,256(%1)\n"
>   		"   la    %2,256(%2)\n"
> -		"2: mvcp  0(%0,%2),0(%1),%3\n"
> +		"2: mvcp  0(%0,%2),0(%1),%[key]\n"
>   		"8: jnz   1b\n"
>   		"   j     5f\n"
>   		"3: la    %4,255(%1)\n"	/* %4 = ptr + 255 */
> @@ -115,7 +117,7 @@ static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
>   		"   slgr  %4,%1\n"
>   		"   clgr  %0,%4\n"	/* copy crosses next page boundary? */
>   		"   jnh   6f\n"
> -		"4: mvcp  0(%4,%2),0(%1),%3\n"
> +		"4: mvcp  0(%4,%2),0(%1),%[key]\n"
>   		"9: slgr  %0,%4\n"
>   		"   j     6f\n"
>   		"5: slgr  %0,%0\n"
> @@ -123,24 +125,36 @@ static inline unsigned long copy_from_user_mvcp(void *x, const void __user *ptr,
>   		EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,6b)
>   		EX_TABLE(7b,3b) EX_TABLE(8b,3b) EX_TABLE(9b,6b)
>   		: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
> -		: : "cc", "memory");
> +		: [key] "d" (key << 4)
> +		: "cc", "memory");
>   	return size;
>   }
>   
>   unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>   {
>   	if (copy_with_mvcos())
> -		return copy_from_user_mvcos(to, from, n);
> -	return copy_from_user_mvcp(to, from, n);
> +		return copy_from_user_mvcos(to, from, n, 0);
> +	return copy_from_user_mvcp(to, from, n, 0);
>   }
>   EXPORT_SYMBOL(raw_copy_from_user);
>   
> -static inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
> -					       unsigned long size)
> +unsigned long raw_copy_from_user_with_key(void *to, const void __user *from,
> +					  unsigned long n, char key)
> +{
> +	if (copy_with_mvcos())
> +		return copy_from_user_mvcos(to, from, n, key);
> +	return copy_from_user_mvcp(to, from, n, key);
> +}
> +EXPORT_SYMBOL(raw_copy_from_user_with_key);
> +
> +inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
> +					unsigned long size, char key)
>   {
>   	unsigned long tmp1, tmp2;
>   	union oac spec = {
> +		.oac1.key = key,
>   		.oac1.as = PSW_BITS_AS_SECONDARY,
> +		.oac1.k = 1,
>   		.oac1.a = 1,
>   	};
>   
> @@ -171,19 +185,19 @@ static inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
>   }
>   
>   static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
> -					      unsigned long size)
> +					      unsigned long size, char key)
>   {
>   	unsigned long tmp1, tmp2;
>   
>   	tmp1 = -256UL;
>   	asm volatile(
>   		"   sacf  0\n"
> -		"0: mvcs  0(%0,%1),0(%2),%3\n"
> +		"0: mvcs  0(%0,%1),0(%2),%[key]\n"
>   		"7: jz    5f\n"
>   		"1: algr  %0,%3\n"
>   		"   la    %1,256(%1)\n"
>   		"   la    %2,256(%2)\n"
> -		"2: mvcs  0(%0,%1),0(%2),%3\n"
> +		"2: mvcs  0(%0,%1),0(%2),%[key]\n"
>   		"8: jnz   1b\n"
>   		"   j     5f\n"
>   		"3: la    %4,255(%1)\n" /* %4 = ptr + 255 */
> @@ -192,7 +206,7 @@ static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
>   		"   slgr  %4,%1\n"
>   		"   clgr  %0,%4\n"	/* copy crosses next page boundary? */
>   		"   jnh   6f\n"
> -		"4: mvcs  0(%4,%1),0(%2),%3\n"
> +		"4: mvcs  0(%4,%1),0(%2),%[key]\n"
>   		"9: slgr  %0,%4\n"
>   		"   j     6f\n"
>   		"5: slgr  %0,%0\n"
> @@ -200,17 +214,26 @@ static inline unsigned long copy_to_user_mvcs(void __user *ptr, const void *x,
>   		EX_TABLE(0b,3b) EX_TABLE(2b,3b) EX_TABLE(4b,6b)
>   		EX_TABLE(7b,3b) EX_TABLE(8b,3b) EX_TABLE(9b,6b)
>   		: "+a" (size), "+a" (ptr), "+a" (x), "+a" (tmp1), "=a" (tmp2)
> -		: : "cc", "memory");
> +		: [key] "d" (key << 4)
> +		: "cc", "memory");
>   	return size;
>   }
>   
>   unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n)
>   {
>   	if (copy_with_mvcos())
> -		return copy_to_user_mvcos(to, from, n);
> -	return copy_to_user_mvcs(to, from, n);
> +		return copy_to_user_mvcos(to, from, n, 0);
> +	return copy_to_user_mvcs(to, from, n, 0);
>   }
>   EXPORT_SYMBOL(raw_copy_to_user);
> +unsigned long raw_copy_to_user_with_key(void __user *to, const void *from,
> +					unsigned long n, char key)
> +{
> +	if (copy_with_mvcos())
> +		return copy_to_user_mvcos(to, from, n, key);
> +	return copy_to_user_mvcs(to, from, n, key);
> +}
> +EXPORT_SYMBOL(raw_copy_to_user_with_key);
>   
>   static inline unsigned long clear_user_mvcos(void __user *to, unsigned long size)
>   {
>