Subject: [PATCH 1/8] powerpc/uaccess: Add unsafe_copy_from_user

From: "Christopher M. Riedl" <[email-masked]>
Date: Thu, 15 Oct 2020 10:01:52 -0500

Implement raw_copy_from_user_allowed() which assumes that userspace read
access is open. Use this new function to implement raw_copy_from_user().
Finally, wrap the new function to follow the usual "unsafe_" convention
of taking a label argument. The new raw_copy_from_user_allowed() calls
__copy_tofrom_user() internally, but this is still safe to call in user
access blocks formed with user_*_access_begin()/user_*_access_end()
since asm functions are not instrumented for tracing.

Signed-off-by: Christopher M. Riedl <[email-masked]>
---
 arch/powerpc/include/asm/uaccess.h | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 26781b044932..66940b4eb692 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -418,38 +418,45 @@ raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
 }
 #endif /* __powerpc64__ */
 
-static inline unsigned long raw_copy_from_user(void *to,
-		const void __user *from, unsigned long n)
+static inline unsigned long
+raw_copy_from_user_allowed(void *to, const void __user *from, unsigned long n)
 {
-	unsigned long ret;
 	if (__builtin_constant_p(n) && (n <= 8)) {
-		ret = 1;
+		unsigned long ret = 1;
 
 		switch (n) {
 		case 1:
 			barrier_nospec();
-			__get_user_size(*(u8 *)to, from, 1, ret);
+			__get_user_size_allowed(*(u8 *)to, from, 1, ret);
 			break;
 		case 2:
 			barrier_nospec();
-			__get_user_size(*(u16 *)to, from, 2, ret);
+			__get_user_size_allowed(*(u16 *)to, from, 2, ret);
 			break;
 		case 4:
 			barrier_nospec();
-			__get_user_size(*(u32 *)to, from, 4, ret);
+			__get_user_size_allowed(*(u32 *)to, from, 4, ret);
 			break;
 		case 8:
 			barrier_nospec();
-			__get_user_size(*(u64 *)to, from, 8, ret);
+			__get_user_size_allowed(*(u64 *)to, from, 8, ret);
 			break;
 		}
 		if (ret == 0)
 			return 0;
 	}
 
+	return __copy_tofrom_user((__force void __user *)to, from, n);
+}
+
+static inline unsigned long
+raw_copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	unsigned long ret;
+
 	barrier_nospec();
 	allow_read_from_user(from, n);
-	ret = __copy_tofrom_user((__force void __user *)to, from, n);
+	ret = raw_copy_from_user_allowed(to, from, n);
 	prevent_read_from_user(from, n);
 	return ret;
 }
@@ -571,6 +578,9 @@ user_write_access_begin(const void __user *ptr, size_t len)
 #define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
 #define unsafe_put_user(x, p, e) __put_user_goto(x, p, e)
 
+#define unsafe_copy_from_user(d, s, l, e) \
+	unsafe_op_wrap(raw_copy_from_user_allowed(d, s, l), e)
+
 #define unsafe_copy_to_user(d, s, l, e) \
 do {									\
 	u8 __user *_dst = (u8 __user *)(d);				\
-- 
2.28.0