[RFC PATCH v2 18/24] x86/uaccess: Add unsafe_copy_from_user() implementation

[Jens Remus <jremus@linux.ibm.com>]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Add an x86 implementation of unsafe_copy_from_user() similar to the
existing unsafe_copy_to_user().

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Cherry-picked from "[PATCH v16 00/20] unwind_deferred: Implement sframe
    handling" series:
    https://lore.kernel.org/all/20260521142546.3908498-5-jremus@linux.ibm.com/

 arch/x86/include/asm/uaccess.h | 39 +++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 3a0dd3c2b233..235886106f31 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -598,7 +598,7 @@ _label:									\
  * We want the unsafe accessors to always be inlined and use
  * the error labels - thus the macro games.
  */
-#define unsafe_copy_loop(dst, src, len, type, label)				\
+#define unsafe_copy_to_user_loop(dst, src, len, type, label)			\
 	while (len >= sizeof(type)) {						\
 		unsafe_put_user(*(type *)(src),(type __user *)(dst),label);	\
 		dst += sizeof(type);						\
@@ -606,15 +606,34 @@ _label:									\
 		len -= sizeof(type);						\
 	}
 
-#define unsafe_copy_to_user(_dst,_src,_len,label)			\
-do {									\
-	char __user *__ucu_dst = (_dst);				\
-	const char *__ucu_src = (_src);					\
-	size_t __ucu_len = (_len);					\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
+#define unsafe_copy_to_user(_dst, _src, _len, label)				\
+do {										\
+	void __user *__dst = (_dst);						\
+	const void *__src = (_src);						\
+	size_t __len = (_len);							\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u64, label);		\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u32, label);		\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u16, label);		\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u8,  label);		\
+} while (0)
+
+#define unsafe_copy_from_user_loop(dst, src, len, type, label)			\
+	while (len >= sizeof(type)) {						\
+		unsafe_get_user(*(type *)(dst), (type __user *)(src), label);	\
+		dst += sizeof(type);						\
+		src += sizeof(type);						\
+		len -= sizeof(type);						\
+	}
+
+#define unsafe_copy_from_user(_dst, _src, _len, label)				\
+do {										\
+	void *__dst = (_dst);							\
+	const void __user *__src = (_src);					\
+	size_t __len = (_len);							\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u64, label);		\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u32, label);		\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u16, label);		\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u8,  label);		\
 } while (0)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-- 
2.53.0