[RFC PATCH 2/2] s390/uaccess: Provide raw_copy_from/to_user_opaque

[Janis Schoetterl-Glausch]

This enables KVM to perform key checked guest accesses by passing the
access key via the opaque argument of __copy_from/to_user_opaque.
Since the existing uaccess implementation on s390 makes use of move
instructions that support having an additional access key supplied,
we can implement raw_copy_from/to_user_opaque by enhancing the
existing implementation.

Signed-off-by: Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx>
---
 arch/s390/include/asm/uaccess.h | 27 ++++++++++++++--
 arch/s390/lib/uaccess.c         | 56 ++++++++++++++++++++-------------
 2 files changed, 60 insertions(+), 23 deletions(-)

diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index 02b467461163..1a324bc3ae0b 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -33,11 +33,34 @@ static inline int __range_ok(unsigned long addr, unsigned long size)
 
 #define access_ok(addr, size) __access_ok(addr, size)
 
+#define uaccess_opaque uaccess_opaque
+struct uaccess_opaque {
+	u8 key;
+};
+
 unsigned long __must_check
-raw_copy_from_user(void *to, const void __user *from, unsigned long n);
+raw_copy_from_user_opaque(void *to, const void __user *from, unsigned long n,
+			  struct uaccess_opaque opaque);
 
 unsigned long __must_check
-raw_copy_to_user(void __user *to, const void *from, unsigned long n);
+raw_copy_to_user_opaque(void __user *to, const void *from, unsigned long n,
+			struct uaccess_opaque opaque);
+
+static __always_inline unsigned long __must_check
+raw_copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	struct uaccess_opaque opaque = { .key = 0};
+
+	return raw_copy_from_user_opaque(to, from, n, opaque);
+}
+
+static __always_inline unsigned long __must_check
+raw_copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	struct uaccess_opaque opaque = { .key = 0};
+
+	return raw_copy_to_user_opaque(to, from, n, opaque);
+}
 
 #ifndef CONFIG_KASAN
 #define INLINE_COPY_FROM_USER
diff --git a/arch/s390/lib/uaccess.c b/arch/s390/lib/uaccess.c
index d3a700385875..6446634c3b75 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, u8 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, u8 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 +125,31 @@ 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)
+unsigned long raw_copy_from_user_opaque(void *to, const void __user *from,
+					unsigned long n,
+					struct uaccess_opaque opaque)
 {
+	u8 key = opaque.key;
+
 	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, key);
+	return copy_from_user_mvcp(to, from, n, key);
 }
-EXPORT_SYMBOL(raw_copy_from_user);
+EXPORT_SYMBOL(raw_copy_from_user_opaque);
 
-static inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
-					       unsigned long size)
+inline unsigned long copy_to_user_mvcos(void __user *ptr, const void *x,
+					unsigned long size, u8 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 +180,19 @@ 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, u8 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 +201,7 @@ 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 +209,22 @@ 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)
+unsigned long raw_copy_to_user_opaque(void __user *to, const void *from,
+				      unsigned long n,
+				      struct uaccess_opaque opaque)
 {
+	u8 key = opaque.key;
+
 	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, key);
+	return copy_to_user_mvcs(to, from, n, key);
 }
-EXPORT_SYMBOL(raw_copy_to_user);
+EXPORT_SYMBOL(raw_copy_to_user_opaque);
 
 static inline unsigned long clear_user_mvcos(void __user *to, unsigned long size)
 {
-- 
2.32.0