[PATCH v2] uaccess: decouple INLINE_COPY_FROM_USER and CONFIG_RUST

["Yury Norov (NVIDIA)" <yury.norov@gmail.com>]

Commit 1f9a8286bc0c ("uaccess: always export _copy_[from|to]_user with
CONFIG_RUST") exports _copy_{from,to}_user() unconditionally, if RUST
is enabled. This pollutes exported symbols namespace, and spreads RUST
ifdefery in core files.

It's better to declare a corresponding helper under the rust/helpers,
similarly to how non-underscored copy_{from,to}_user() is handled.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
---
v2: drop rust part of comment for _copy_from_user() (Alice)

Andrew,

Can you kindly re-apply?

Thanks,
Yury

 include/linux/uaccess.h |  2 --
 lib/usercopy.c          |  4 ++--
 rust/helpers/uaccess.c  | 12 ++++++++++++
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 1beb5b395d81..01cbd7dd0ba3 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -152,8 +152,6 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
  * directly in the normal copy_to/from_user(), the other ones go
  * through an extern _copy_to/from_user(), which expands the same code
  * here.
- *
- * rust code always uses the extern definition.
  */
 static inline __must_check unsigned long
 _inline_copy_from_user(void *to, const void __user *from, unsigned long n)
diff --git a/lib/usercopy.c b/lib/usercopy.c
index 7b17b83c8042..b00a3a957de6 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -12,7 +12,7 @@
 
 /* out-of-line parts */
 
-#if !defined(INLINE_COPY_FROM_USER) || defined(CONFIG_RUST)
+#if !defined(INLINE_COPY_FROM_USER)
 unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	return _inline_copy_from_user(to, from, n);
@@ -20,7 +20,7 @@ unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n
 EXPORT_SYMBOL(_copy_from_user);
 #endif
 
-#if !defined(INLINE_COPY_TO_USER) || defined(CONFIG_RUST)
+#if !defined(INLINE_COPY_TO_USER)
 unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	return _inline_copy_to_user(to, from, n);
diff --git a/rust/helpers/uaccess.c b/rust/helpers/uaccess.c
index f49076f813cd..4629b2d15529 100644
--- a/rust/helpers/uaccess.c
+++ b/rust/helpers/uaccess.c
@@ -13,3 +13,15 @@ unsigned long rust_helper_copy_to_user(void __user *to, const void *from,
 {
 	return copy_to_user(to, from, n);
 }
+
+#ifdef INLINE_COPY_FROM_USER
+unsigned long rust_helper__copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	return _inline_copy_from_user(to, from, n);
+}
+
+unsigned long rust_helper__copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	return _inline_copy_to_user(to, from, n);
+}
+#endif
-- 
2.43.0