powerpc: Add a framework for Kernel Userspace Access Protection

This patch implements a framework for Kernel Userspace Access
Protection.

Then subarches will have the possibility to provide their own
implementation by providing setup_kuap() and
allow/prevent_user_access().

Some platforms will need to know the area accessed and whether it is
accessed from read, write or both. Therefore source, destination and
size and handed over to the two functions.

mpe: Rename to allow/prevent rather than unlock/lock, and add
read/write wrappers. Drop the 32-bit code for now until we have an
implementation for it. Add kuap to pt_regs for 64-bit as well as
32-bit. Don't split strings, use pr_crit_ratelimited().

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 30 insertions, 8 deletions

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 4d6d905e9138..76f34346b642 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -6,6 +6,7 @@
 #include <asm/processor.h>
 #include <asm/page.h>
 #include <asm/extable.h>
+#include <asm/kup.h>
 
 /*
  * The fs value determines whether argument validity checking should be
@@ -140,6 +141,7 @@ extern long __put_user_bad(void);
 #define __put_user_size(x, ptr, size, retval)			\
 do {								\
 	retval = 0;						\
+	allow_write_to_user(ptr, size);				\
 	switch (size) {						\
 	  case 1: __put_user_asm(x, ptr, retval, "stb"); break;	\
 	  case 2: __put_user_asm(x, ptr, retval, "sth"); break;	\
@@ -147,6 +149,7 @@ do {								\
 	  case 8: __put_user_asm2(x, ptr, retval); break;	\
 	  default: __put_user_bad();				\
 	}							\
+	prevent_write_to_user(ptr, size);			\
 } while (0)
 
 #define __put_user_nocheck(x, ptr, size)			\
@@ -239,6 +242,7 @@ do {								\
 	__chk_user_ptr(ptr);					\
 	if (size > sizeof(x))					\
 		(x) = __get_user_bad();				\
+	allow_read_from_user(ptr, size);			\
 	switch (size) {						\
 	case 1: __get_user_asm(x, ptr, retval, "lbz"); break;	\
 	case 2: __get_user_asm(x, ptr, retval, "lhz"); break;	\
@@ -246,6 +250,7 @@ do {								\
 	case 8: __get_user_asm2(x, ptr, retval);  break;	\
 	default: (x) = __get_user_bad();			\
 	}							\
+	prevent_read_from_user(ptr, size);			\
 } while (0)
 
 /*
@@ -305,15 +310,21 @@ extern unsigned long __copy_tofrom_user(void __user *to,
 static inline unsigned long
 raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
 {
-	return __copy_tofrom_user(to, from, n);
+	unsigned long ret;
+
+	allow_user_access(to, from, n);
+	ret = __copy_tofrom_user(to, from, n);
+	prevent_user_access(to, from, n);
+	return ret;
 }
 #endif /* __powerpc64__ */
 
 static inline unsigned long raw_copy_from_user(void *to,
 		const void __user *from, unsigned long n)
 {
+	unsigned long ret;
 	if (__builtin_constant_p(n) && (n <= 8)) {
-		unsigned long ret = 1;
+		ret = 1;
 
 		switch (n) {
 		case 1:
@@ -338,14 +349,18 @@ static inline unsigned long raw_copy_from_user(void *to,
 	}
 
 	barrier_nospec();
-	return __copy_tofrom_user((__force void __user *)to, from, n);
+	allow_read_from_user(from, n);
+	ret = __copy_tofrom_user((__force void __user *)to, from, n);
+	prevent_read_from_user(from, n);
+	return ret;
 }
 
 static inline unsigned long raw_copy_to_user(void __user *to,
 		const void *from, unsigned long n)
 {
+	unsigned long ret;
 	if (__builtin_constant_p(n) && (n <= 8)) {
-		unsigned long ret = 1;
+		ret = 1;
 
 		switch (n) {
 		case 1:
@@ -365,17 +380,24 @@ static inline unsigned long raw_copy_to_user(void __user *to,
 			return 0;
 	}
 
-	return __copy_tofrom_user(to, (__force const void __user *)from, n);
+	allow_write_to_user(to, n);
+	ret = __copy_tofrom_user(to, (__force const void __user *)from, n);
+	prevent_write_to_user(to, n);
+	return ret;
 }
 
 extern unsigned long __clear_user(void __user *addr, unsigned long size);
 
 static inline unsigned long clear_user(void __user *addr, unsigned long size)
 {
+	unsigned long ret = size;
 	might_fault();
-	if (likely(access_ok(addr, size)))
-		return __clear_user(addr, size);
-	return size;
+	if (likely(access_ok(addr, size))) {
+		allow_write_to_user(addr, size);
+		ret = __clear_user(addr, size);
+		prevent_write_to_user(addr, size);
+	}
+	return ret;
 }
 
 extern long strncpy_from_user(char *dst, const char __user *src, long count);