[PATCH v2 0/5] uaccess: Updates to scoped_user_access()

[PATCH v2 0/5] uaccess: Updates to scoped_user_access()

[david.laight.linux]

From: David Laight <david.laight.linux@gmail.com>

Converting kernel/signal.c to use scoped_user_access() had compilation
warnings because some of the pointers are 'pointer to const'.
This is fixed in patch 1.

The same problem has been found compiling arch/powerpc/lib/checksum_wrappers.c

For v2 I've changed the code to use 'auto' and replaced the over-complex
CLASS definition (and its for loop) with a much simpler __cleanup() function
on the second loop.

Patches 2 and 3 factor out the 'autoterminating nested for loops'.
I'm sure there'll be a 'bikeshed' discussion about the names.

Patch 4 stops warnings from -Wshadow (enabled by W=2).
I did think about making the _diag_xxx conditional on a W=2 build,
but since the pre-processor just emits #pragma lines and they are
smaller that the for() loop it doesn't seem worth while.

Patch 5 is the change to signal.c that prompted patch 1.
The generated code looks fine, but I've not tested it.
Most of the changes are to 'compat' code - so are probably not
usually performance critical.
IIRC the non-compat code uses copy_to/from_user() for the structures
so is probably slower than the compat code's member by member copy.

David Laight (5):
  uaccess: Fix scoped_user_read_access() for 'pointer to const'
  compiler.h: Add generic support for 'autoterminating nested for()
    loops'
  uaccess.h: Use with() and and_with() in __scoped_user_access()
  uaccess: Disable -Wshadow in __scoped_user_access()
  signal: Use scoped_user_access() instead of __put/get_user()

 include/linux/compiler.h | 26 +++++++++++++++
 include/linux/uaccess.h  | 51 ++++++++++------------------
 kernel/signal.c          | 72 +++++++++++++++++++++++-----------------
 3 files changed, 86 insertions(+), 63 deletions(-)

-- 
2.39.5

[PATCH v2 1/5] uaccess: Fix scoped_user_read_access() for 'pointer to const'

[david.laight.linux]

From: David Laight <david.laight.linux@gmail.com>

If a 'const struct foo __user *ptr' is used for the address passed
to scoped_user_read_access() then you get a warning/error
uaccess.h:691:1: error: initialization discards 'const' qualifier
    from pointer target type [-Werror=discarded-qualifiers]
for the
    void __user *_tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl)
assignment.

Fix by using 'auto' for both _tmpptr and the redeclaration of uptr.
Replace the CLASS() with explicit __cleanup() functions on uptr.

Fixes: e497310b4ffb "(uaccess: Provide scoped user access regions)"
Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 include/linux/uaccess.h | 54 +++++++++++++++--------------------------
 1 file changed, 20 insertions(+), 34 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 1f3804245c06..809e4f7dfdbd 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -647,36 +647,22 @@ static inline void user_access_restore(unsigned long flags) { }
 /* Define RW variant so the below _mode macro expansion works */
 #define masked_user_rw_access_begin(u)	masked_user_access_begin(u)
 #define user_rw_access_begin(u, s)	user_access_begin(u, s)
-#define user_rw_access_end()		user_access_end()
 
 /* Scoped user access */
-#define USER_ACCESS_GUARD(_mode)				\
-static __always_inline void __user *				\
-class_user_##_mode##_begin(void __user *ptr)			\
-{								\
-	return ptr;						\
-}								\
-								\
-static __always_inline void					\
-class_user_##_mode##_end(void __user *ptr)			\
-{								\
-	user_##_mode##_access_end();				\
-}								\
-								\
-DEFINE_CLASS(user_ ##_mode## _access, void __user *,		\
-	     class_user_##_mode##_end(_T),			\
-	     class_user_##_mode##_begin(ptr), void __user *ptr)	\
-								\
-static __always_inline class_user_##_mode##_access_t		\
-class_user_##_mode##_access_ptr(void __user *scope)		\
-{								\
-	return scope;						\
-}
 
-USER_ACCESS_GUARD(read)
-USER_ACCESS_GUARD(write)
-USER_ACCESS_GUARD(rw)
-#undef USER_ACCESS_GUARD
+/* Cleanup wrapper functions */
+static __always_inline void __scoped_user_read_access_end(const void *p)
+{
+	user_read_access_end();
+};
+static __always_inline void __scoped_user_write_access_end(const void *p)
+{
+	user_write_access_end();
+};
+static __always_inline void __scoped_user_rw_access_end(const void *p)
+{
+	user_access_end();
+};
 
 /**
  * __scoped_user_access_begin - Start a scoped user access
@@ -750,13 +736,13 @@ USER_ACCESS_GUARD(rw)
  *
  * Don't use directly. Use scoped_masked_user_$MODE_access() instead.
  */
-#define __scoped_user_access(mode, uptr, size, elbl)					\
-for (bool done = false; !done; done = true)						\
-	for (void __user *_tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl); \
-	     !done; done = true)							\
-		for (CLASS(user_##mode##_access, scope)(_tmpptr); !done; done = true)	\
-			/* Force modified pointer usage within the scope */		\
-			for (const typeof(uptr) uptr = _tmpptr; !done; done = true)
+#define __scoped_user_access(mode, uptr, size, elbl)				\
+for (bool done = false; !done; done = true)					\
+	for (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl);	\
+	     !done; done = true)						\
+		/* Force modified pointer usage within the scope */		\
+		for (const auto uptr  __cleanup(__scoped_user_##mode##_access_end) = \
+		     _tmpptr; !done; done = true)
 
 /**
  * scoped_user_read_access_size - Start a scoped user read access with given size
-- 
2.39.5

[PATCH v2 2/5] compiler.h: Add generic support for 'autoterminating nested for() loops'

[david.laight.linux]

From: David Laight <david.laight.linux@gmail.com>

Autoterminating nested for() loops can be used inside #defines to
declare variables that are scoped to the statement that follows.
These are used by __scoped_user_access() but may have other uses
and the gory details are best separated from the use.

Using 'with (declaration)' and 'and_with (declaration)' seems to
read reasonably well and doesn't seem to collide with any existing
code.

As an example the scoped user access definition becomes:
	with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl)) \
		/* Force modified pointer usage within the scope */		\
		and_with (const auto uptr __cleanup(...) = _tmpptr)

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 include/linux/compiler.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index af16624b29fd..1098a91b5591 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -369,6 +369,32 @@ static inline void *offset_to_ptr(const int *off)
  */
 #define prevent_tail_call_optimization()	mb()
 
+/*
+ * Sometimes a #define needs to declare a variable that is scoped
+ * to the statement that follows without having mismatched {}.
+ *	with (int x = expression) {
+ *		statements
+ *	}
+ * is the same as:
+ *	{
+ *		int x = expression;
+ *		statements
+ *	}
+ * but lets it all be hidden from the call site, eg:
+ *	frobnicate(x, args) {
+ *		statements
+ *	} 
+ * Only a single variable can be defined, and_with() allows extra ones
+ * without adding an additional outer loop.
+ *
+ * The controlled scope can be terminated using return, break, continue or goto.
+ */
+#define with(declaration) \
+	for (bool _with_done = false; !_with_done; _with_done = true)	\
+		and_with (declaration)
+#define and_with(declaration) \
+	for (declaration; !_with_done; _with_done = true)
+
 #include <asm/rwonce.h>
 
 #endif /* __LINUX_COMPILER_H */
-- 
2.39.5

[PATCH v2 3/5] uaccess.h: Use with() and and_with() in __scoped_user_access()

[david.laight.linux]

From: David Laight <david.laight.linux@gmail.com>

Wrappers for autoterminating nested for() loops have been added to
compiler.h, use them to hide the gory details.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 include/linux/uaccess.h | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 809e4f7dfdbd..64bc2492eb99 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -736,13 +736,10 @@ static __always_inline void __scoped_user_rw_access_end(const void *p)
  *
  * Don't use directly. Use scoped_masked_user_$MODE_access() instead.
  */
-#define __scoped_user_access(mode, uptr, size, elbl)				\
-for (bool done = false; !done; done = true)					\
-	for (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl);	\
-	     !done; done = true)						\
-		/* Force modified pointer usage within the scope */		\
-		for (const auto uptr  __cleanup(__scoped_user_##mode##_access_end) = \
-		     _tmpptr; !done; done = true)
+#define __scoped_user_access(mode, uptr, size, elbl)					\
+	with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))	\
+		/* Force modified pointer usage within the scope */			\
+		and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr)
 
 /**
  * scoped_user_read_access_size - Start a scoped user read access with given size
-- 
2.39.5

[PATCH v2 4/5] uaccess: Disable -Wshadow in __scoped_user_access()

[david.laight.linux]

From: David Laight <david.laight.linux@gmail.com>

-Wshadow is enabled by W=2 builds and __scoped_user_access() quite
deliberately creates a 'const' shadow of the 'user' address that
references a 'guard page' when the application passes a kernel pointer.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 include/linux/uaccess.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 64bc2492eb99..445391ec5a6d 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -739,7 +739,9 @@ static __always_inline void __scoped_user_rw_access_end(const void *p)
 #define __scoped_user_access(mode, uptr, size, elbl)					\
 	with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))	\
 		/* Force modified pointer usage within the scope */			\
-		and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr)
+		__diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")	\
+		and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
+		__diag_pop()
 
 /**
  * scoped_user_read_access_size - Start a scoped user read access with given size
-- 
2.39.5

[PATCH v2 next 5/5] signal: Use scoped_user_access() instead of __put/get_user()

[david.laight.linux]

From: David Laight <david.laight.linux@gmail.com>

Mechanically change the access_ok() and __get/put_user() to use
scoped_user_read/write_access() and unsafe_get/put_user().

This generates better code with fewer STAC/CLAC pairs.

It also ensures that access_ok() is called near the user accesses.
I failed to find the one for __save_altstack().

Looking at the change, perhaps there should be aliases:
#define scoped_put_user unsafe_put_user
#define scoped_get_user unsafe_get_user

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 kernel/signal.c | 72 ++++++++++++++++++++++++++++---------------------
 1 file changed, 42 insertions(+), 30 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index d65d0fe24bfb..fca257398cbc 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -4469,10 +4469,16 @@ int restore_altstack(const stack_t __user *uss)
 int __save_altstack(stack_t __user *uss, unsigned long sp)
 {
 	struct task_struct *t = current;
-	int err = __put_user((void __user *)t->sas_ss_sp, &uss->ss_sp) |
-		__put_user(t->sas_ss_flags, &uss->ss_flags) |
-		__put_user(t->sas_ss_size, &uss->ss_size);
-	return err;
+
+	scoped_user_write_access(uss, Efault) {
+		unsafe_put_user((void __user *)t->sas_ss_sp, &uss->ss_sp, Efault);
+		unsafe_put_user(t->sas_ss_flags, &uss->ss_flags, Efault);
+		unsafe_put_user(t->sas_ss_size, &uss->ss_size, Efault);
+	}
+	return 0;
+
+Efault:
+	return -EFAULT;
 }
 
 #ifdef CONFIG_COMPAT
@@ -4705,12 +4711,12 @@ SYSCALL_DEFINE3(sigaction, int, sig,
 
 	if (act) {
 		old_sigset_t mask;
-		if (!access_ok(act, sizeof(*act)) ||
-		    __get_user(new_ka.sa.sa_handler, &act->sa_handler) ||
-		    __get_user(new_ka.sa.sa_restorer, &act->sa_restorer) ||
-		    __get_user(new_ka.sa.sa_flags, &act->sa_flags) ||
-		    __get_user(mask, &act->sa_mask))
-			return -EFAULT;
+		scoped_user_read_access(act, Efault) {
+		    unsafe_get_user(new_ka.sa.sa_handler, &act->sa_handler, Efault);
+		    unsafe_get_user(new_ka.sa.sa_restorer, &act->sa_restorer, Efault);
+		    unsafe_get_user(new_ka.sa.sa_flags, &act->sa_flags, Efault);
+		    unsafe_get_user(mask, &act->sa_mask, Efault);
+		}
 #ifdef __ARCH_HAS_KA_RESTORER
 		new_ka.ka_restorer = NULL;
 #endif
@@ -4720,15 +4726,18 @@ SYSCALL_DEFINE3(sigaction, int, sig,
 	ret = do_sigaction(sig, act ? &new_ka : NULL, oact ? &old_ka : NULL);
 
 	if (!ret && oact) {
-		if (!access_ok(oact, sizeof(*oact)) ||
-		    __put_user(old_ka.sa.sa_handler, &oact->sa_handler) ||
-		    __put_user(old_ka.sa.sa_restorer, &oact->sa_restorer) ||
-		    __put_user(old_ka.sa.sa_flags, &oact->sa_flags) ||
-		    __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask))
-			return -EFAULT;
+		scoped_user_write_access(oact, Efault) {
+		    unsafe_put_user(old_ka.sa.sa_handler, &oact->sa_handler, Efault);
+		    unsafe_put_user(old_ka.sa.sa_restorer, &oact->sa_restorer, Efault);
+		    unsafe_put_user(old_ka.sa.sa_flags, &oact->sa_flags, Efault);
+		    unsafe_put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask, Efault);
+		}
 	}
 
 	return ret;
+
+Efault:
+	return -EFAULT;
 }
 #endif
 #ifdef CONFIG_COMPAT_OLD_SIGACTION
@@ -4742,12 +4751,12 @@ COMPAT_SYSCALL_DEFINE3(sigaction, int, sig,
 	compat_uptr_t handler, restorer;
 
 	if (act) {
-		if (!access_ok(act, sizeof(*act)) ||
-		    __get_user(handler, &act->sa_handler) ||
-		    __get_user(restorer, &act->sa_restorer) ||
-		    __get_user(new_ka.sa.sa_flags, &act->sa_flags) ||
-		    __get_user(mask, &act->sa_mask))
-			return -EFAULT;
+		scoped_user_read_access(act, Efault) {
+		    unsafe_get_user(handler, &act->sa_handler, Efault);
+		    unsafe_get_user(restorer, &act->sa_restorer, Efault);
+		    unsafe_get_user(new_ka.sa.sa_flags, &act->sa_flags, Efault);
+		    unsafe_get_user(mask, &act->sa_mask, Efault);
+		}
 
 #ifdef __ARCH_HAS_KA_RESTORER
 		new_ka.ka_restorer = NULL;
@@ -4760,16 +4769,19 @@ COMPAT_SYSCALL_DEFINE3(sigaction, int, sig,
 	ret = do_sigaction(sig, act ? &new_ka : NULL, oact ? &old_ka : NULL);
 
 	if (!ret && oact) {
-		if (!access_ok(oact, sizeof(*oact)) ||
-		    __put_user(ptr_to_compat(old_ka.sa.sa_handler),
-			       &oact->sa_handler) ||
-		    __put_user(ptr_to_compat(old_ka.sa.sa_restorer),
-			       &oact->sa_restorer) ||
-		    __put_user(old_ka.sa.sa_flags, &oact->sa_flags) ||
-		    __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask))
-			return -EFAULT;
+		scoped_user_write_access(oact, Efault) {
+		    unsafe_put_user(ptr_to_compat(old_ka.sa.sa_handler),
+			       &oact->sa_handler, Efault);
+		    unsafe_put_user(ptr_to_compat(old_ka.sa.sa_restorer),
+			       &oact->sa_restorer, Efault);
+		    unsafe_put_user(old_ka.sa.sa_flags, &oact->sa_flags, Efault);
+		    unsafe_put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask, Efault);
+		}
 	}
 	return ret;
+
+Efault:
+	return -EFAULT;
 }
 #endif
 
-- 
2.39.5

Re: [PATCH v2 1/5] uaccess: Fix scoped_user_read_access() for 'pointer to const'

[Christophe Leroy (CS GROUP)]

Le 02/03/2026 à 14:27, david.laight.linux@gmail.com a écrit :
> From: David Laight <david.laight.linux@gmail.com>
> 
> If a 'const struct foo __user *ptr' is used for the address passed
> to scoped_user_read_access() then you get a warning/error
> uaccess.h:691:1: error: initialization discards 'const' qualifier
>      from pointer target type [-Werror=discarded-qualifiers]
> for the
>      void __user *_tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl)
> assignment.
> 
> Fix by using 'auto' for both _tmpptr and the redeclaration of uptr.
> Replace the CLASS() with explicit __cleanup() functions on uptr.
> 
> Fixes: e497310b4ffb "(uaccess: Provide scoped user access regions)"
> Signed-off-by: David Laight <david.laight.linux@gmail.com>

Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Tested-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>

Can we get this fix merged in 7.0-rc3 so that we can start building 7.1 
on top of it ?

Thanks
Christophe

> ---
>   include/linux/uaccess.h | 54 +++++++++++++++--------------------------
>   1 file changed, 20 insertions(+), 34 deletions(-)
> 
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 1f3804245c06..809e4f7dfdbd 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -647,36 +647,22 @@ static inline void user_access_restore(unsigned long flags) { }
>   /* Define RW variant so the below _mode macro expansion works */
>   #define masked_user_rw_access_begin(u)	masked_user_access_begin(u)
>   #define user_rw_access_begin(u, s)	user_access_begin(u, s)
> -#define user_rw_access_end()		user_access_end()
>   
>   /* Scoped user access */
> -#define USER_ACCESS_GUARD(_mode)				\
> -static __always_inline void __user *				\
> -class_user_##_mode##_begin(void __user *ptr)			\
> -{								\
> -	return ptr;						\
> -}								\
> -								\
> -static __always_inline void					\
> -class_user_##_mode##_end(void __user *ptr)			\
> -{								\
> -	user_##_mode##_access_end();				\
> -}								\
> -								\
> -DEFINE_CLASS(user_ ##_mode## _access, void __user *,		\
> -	     class_user_##_mode##_end(_T),			\
> -	     class_user_##_mode##_begin(ptr), void __user *ptr)	\
> -								\
> -static __always_inline class_user_##_mode##_access_t		\
> -class_user_##_mode##_access_ptr(void __user *scope)		\
> -{								\
> -	return scope;						\
> -}
>   
> -USER_ACCESS_GUARD(read)
> -USER_ACCESS_GUARD(write)
> -USER_ACCESS_GUARD(rw)
> -#undef USER_ACCESS_GUARD
> +/* Cleanup wrapper functions */
> +static __always_inline void __scoped_user_read_access_end(const void *p)
> +{
> +	user_read_access_end();
> +};
> +static __always_inline void __scoped_user_write_access_end(const void *p)
> +{
> +	user_write_access_end();
> +};
> +static __always_inline void __scoped_user_rw_access_end(const void *p)
> +{
> +	user_access_end();
> +};
>   
>   /**
>    * __scoped_user_access_begin - Start a scoped user access
> @@ -750,13 +736,13 @@ USER_ACCESS_GUARD(rw)
>    *
>    * Don't use directly. Use scoped_masked_user_$MODE_access() instead.
>    */
> -#define __scoped_user_access(mode, uptr, size, elbl)					\
> -for (bool done = false; !done; done = true)						\
> -	for (void __user *_tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl); \
> -	     !done; done = true)							\
> -		for (CLASS(user_##mode##_access, scope)(_tmpptr); !done; done = true)	\
> -			/* Force modified pointer usage within the scope */		\
> -			for (const typeof(uptr) uptr = _tmpptr; !done; done = true)
> +#define __scoped_user_access(mode, uptr, size, elbl)				\
> +for (bool done = false; !done; done = true)					\
> +	for (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl);	\
> +	     !done; done = true)						\
> +		/* Force modified pointer usage within the scope */		\
> +		for (const auto uptr  __cleanup(__scoped_user_##mode##_access_end) = \
> +		     _tmpptr; !done; done = true)
>   
>   /**
>    * scoped_user_read_access_size - Start a scoped user read access with given size

Re: [PATCH v2 4/5] uaccess: Disable -Wshadow in __scoped_user_access()

[Christophe Leroy (CS GROUP)]

Le 02/03/2026 à 14:27, david.laight.linux@gmail.com a écrit :
> From: David Laight <david.laight.linux@gmail.com>
> 
> -Wshadow is enabled by W=2 builds and __scoped_user_access() quite
> deliberately creates a 'const' shadow of the 'user' address that
> references a 'guard page' when the application passes a kernel pointer.
> 
> Signed-off-by: David Laight <david.laight.linux@gmail.com>

There is a problem with this patch:

   DESCEND objtool
   INSTALL libsubcmd_headers
   CALL    scripts/checksyscalls.sh
   CC      kernel/futex/core.o
In file included from ./include/asm-generic/div64.h:27,
                  from ./arch/powerpc/include/generated/asm/div64.h:1,
                  from ./include/linux/math.h:6,
                  from ./include/linux/math64.h:6,
                  from ./include/linux/time.h:6,
                  from ./include/linux/compat.h:10,
                  from kernel/futex/core.c:34:
kernel/futex/futex.h: In function 'futex_get_value_locked':
./include/linux/uaccess.h:740:20: warning: unused variable '_tmpptr' 
[-Wunused-variable]
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |                    ^~~~~~~
./include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
   396 |         for (declaration; !_with_done; _with_done = true)
       |              ^~~~~~~~~~~
./include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |         ^~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
   288 |         return get_user_inline(*dest, from);
       |                ^~~~~~~~~~~~~~~
./include/linux/compiler.h:396:9: warning: this 'for' clause does not 
guard... [-Wmisleading-indentation]
   396 |         for (declaration; !_with_done; _with_done = true)
       |         ^~~
./include/linux/compiler.h:394:17: note: in expansion of macro 'and_with'
   394 |                 and_with (declaration)
       |                 ^~~~~~~~
./include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |         ^~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
   288 |         return get_user_inline(*dest, from);
       |                ^~~~~~~~~~~~~~~
In file included from ././include/linux/compiler_types.h:173,
                  from <command-line>:
./include/linux/compiler-gcc.h:118:33: note: ...this statement, but the 
latter is misleadingly indented as if it were guarded by the 'for'
   118 | #define __diag(s)               _Pragma(__diag_str(GCC 
diagnostic s))
       |                                 ^~~~~~~
./include/linux/compiler-gcc.h:129:9: note: in expansion of macro '__diag'
   129 |         __diag(__diag_GCC_ignore option)
       |         ^~~~~~
./include/linux/uaccess.h:742:31: note: in expansion of macro 
'__diag_ignore_all'
   742 |                 __diag_push() __diag_ignore_all("-Wshadow", 
"uptr is readonly copy")    \
       |                               ^~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
   288 |         return get_user_inline(*dest, from);
       |                ^~~~~~~~~~~~~~~
In file included from ./include/asm-generic/div64.h:27,
                  from ./arch/powerpc/include/generated/asm/div64.h:1,
                  from ./include/linux/math.h:6,
                  from ./include/linux/math64.h:6,
                  from ./include/linux/time.h:6,
                  from ./include/linux/compat.h:10,
                  from kernel/futex/core.c:34:
./include/linux/uaccess.h:743:90: error: '_tmpptr' undeclared (first use 
in this function)
   743 |                 and_with (const auto uptr 
__cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
       | 
                          ^~~~~~~
./include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
   396 |         for (declaration; !_with_done; _with_done = true)
       |              ^~~~~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
   288 |         return get_user_inline(*dest, from);
       |                ^~~~~~~~~~~~~~~
./include/linux/uaccess.h:743:90: note: each undeclared identifier is 
reported only once for each function it appears in
   743 |                 and_with (const auto uptr 
__cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
       | 
                          ^~~~~~~
./include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
   396 |         for (declaration; !_with_done; _with_done = true)
       |              ^~~~~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
   288 |         return get_user_inline(*dest, from);
       |                ^~~~~~~~~~~~~~~
./include/linux/compiler.h:396:28: error: '_with_done' undeclared (first 
use in this function)
   396 |         for (declaration; !_with_done; _with_done = true)
       |                            ^~~~~~~~~~
./include/linux/uaccess.h:743:17: note: in expansion of macro 'and_with'
   743 |                 and_with (const auto uptr 
__cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
       |                 ^~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
   288 |         return get_user_inline(*dest, from);
       |                ^~~~~~~~~~~~~~~
kernel/futex/core.c: In function 'get_futex_key':
./include/linux/uaccess.h:740:20: warning: unused variable '_tmpptr' 
[-Wunused-variable]
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |                    ^~~~~~~
./include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
   396 |         for (declaration; !_with_done; _with_done = true)
       |              ^~~~~~~~~~~
./include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |         ^~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
   584 |                 if (get_user_inline(node, naddr))
       |                     ^~~~~~~~~~~~~~~
./include/linux/compiler.h:396:9: warning: this 'for' clause does not 
guard... [-Wmisleading-indentation]
   396 |         for (declaration; !_with_done; _with_done = true)
       |         ^~~
./include/linux/compiler.h:394:17: note: in expansion of macro 'and_with'
   394 |                 and_with (declaration)
       |                 ^~~~~~~~
./include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |         ^~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
   584 |                 if (get_user_inline(node, naddr))
       |                     ^~~~~~~~~~~~~~~
In file included from ././include/linux/compiler_types.h:173,
                  from <command-line>:
./include/linux/compiler-gcc.h:118:33: note: ...this statement, but the 
latter is misleadingly indented as if it were guarded by the 'for'
   118 | #define __diag(s)               _Pragma(__diag_str(GCC 
diagnostic s))
       |                                 ^~~~~~~
./include/linux/compiler-gcc.h:129:9: note: in expansion of macro '__diag'
   129 |         __diag(__diag_GCC_ignore option)
       |         ^~~~~~
./include/linux/uaccess.h:742:31: note: in expansion of macro 
'__diag_ignore_all'
   742 |                 __diag_push() __diag_ignore_all("-Wshadow", 
"uptr is readonly copy")    \
       |                               ^~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
   584 |                 if (get_user_inline(node, naddr))
       |                     ^~~~~~~~~~~~~~~
In file included from ./include/asm-generic/div64.h:27,
                  from ./arch/powerpc/include/generated/asm/div64.h:1,
                  from ./include/linux/math.h:6,
                  from ./include/linux/math64.h:6,
                  from ./include/linux/time.h:6,
                  from ./include/linux/compat.h:10,
                  from kernel/futex/core.c:34:
./include/linux/uaccess.h:743:90: error: '_tmpptr' undeclared (first use 
in this function)
   743 |                 and_with (const auto uptr 
__cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
       | 
                          ^~~~~~~
./include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
   396 |         for (declaration; !_with_done; _with_done = true)
       |              ^~~~~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
   584 |                 if (get_user_inline(node, naddr))
       |                     ^~~~~~~~~~~~~~~
./include/linux/compiler.h:396:28: error: '_with_done' undeclared (first 
use in this function)
   396 |         for (declaration; !_with_done; _with_done = true)
       |                            ^~~~~~~~~~
./include/linux/uaccess.h:743:17: note: in expansion of macro 'and_with'
   743 |                 and_with (const auto uptr 
__cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
       |                 ^~~~~~~~
./include/linux/uaccess.h:755:9: note: in expansion of macro 
'__scoped_user_access'
   755 |         __scoped_user_access(read, usrc, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:767:9: note: in expansion of macro 
'scoped_user_read_access_size'
   767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:831:9: note: in expansion of macro 
'scoped_user_read_access'
   831 |         scoped_user_read_access(_tmpsrc, efault)                \
       |         ^~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
   584 |                 if (get_user_inline(node, naddr))
       |                     ^~~~~~~~~~~~~~~
./include/linux/uaccess.h:740:20: warning: unused variable '_tmpptr' 
[-Wunused-variable]
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |                    ^~~~~~~
./include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
   396 |         for (declaration; !_with_done; _with_done = true)
       |              ^~~~~~~~~~~
./include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |         ^~~~
./include/linux/uaccess.h:778:9: note: in expansion of macro 
'__scoped_user_access'
   778 |         __scoped_user_access(write, udst, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:790:9: note: in expansion of macro 
'scoped_user_write_access_size'
   790 |         scoped_user_write_access_size(udst, sizeof(*(udst)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:856:9: note: in expansion of macro 
'scoped_user_write_access'
   856 |         scoped_user_write_access(_tmpdst, efault)               \
       |         ^~~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:604:37: note: in expansion of macro 'put_user_inline'
   604 |                 if (node_updated && put_user_inline(node, naddr))
       |                                     ^~~~~~~~~~~~~~~
./include/linux/compiler.h:396:9: warning: this 'for' clause does not 
guard... [-Wmisleading-indentation]
   396 |         for (declaration; !_with_done; _with_done = true)
       |         ^~~
./include/linux/compiler.h:394:17: note: in expansion of macro 'and_with'
   394 |                 and_with (declaration)
       |                 ^~~~~~~~
./include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
   740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, 
uptr, size, elbl))        \
       |         ^~~~
./include/linux/uaccess.h:778:9: note: in expansion of macro 
'__scoped_user_access'
   778 |         __scoped_user_access(write, udst, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:790:9: note: in expansion of macro 
'scoped_user_write_access_size'
   790 |         scoped_user_write_access_size(udst, sizeof(*(udst)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:856:9: note: in expansion of macro 
'scoped_user_write_access'
   856 |         scoped_user_write_access(_tmpdst, efault)               \
       |         ^~~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:604:37: note: in expansion of macro 'put_user_inline'
   604 |                 if (node_updated && put_user_inline(node, naddr))
       |                                     ^~~~~~~~~~~~~~~
In file included from ././include/linux/compiler_types.h:173,
                  from <command-line>:
./include/linux/compiler-gcc.h:118:33: note: ...this statement, but the 
latter is misleadingly indented as if it were guarded by the 'for'
   118 | #define __diag(s)               _Pragma(__diag_str(GCC 
diagnostic s))
       |                                 ^~~~~~~
./include/linux/compiler-gcc.h:129:9: note: in expansion of macro '__diag'
   129 |         __diag(__diag_GCC_ignore option)
       |         ^~~~~~
./include/linux/uaccess.h:742:31: note: in expansion of macro 
'__diag_ignore_all'
   742 |                 __diag_push() __diag_ignore_all("-Wshadow", 
"uptr is readonly copy")    \
       |                               ^~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:778:9: note: in expansion of macro 
'__scoped_user_access'
   778 |         __scoped_user_access(write, udst, size, elbl)
       |         ^~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:790:9: note: in expansion of macro 
'scoped_user_write_access_size'
   790 |         scoped_user_write_access_size(udst, sizeof(*(udst)), elbl)
       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/linux/uaccess.h:856:9: note: in expansion of macro 
'scoped_user_write_access'
   856 |         scoped_user_write_access(_tmpdst, efault)               \
       |         ^~~~~~~~~~~~~~~~~~~~~~~~
kernel/futex/core.c:604:37: note: in expansion of macro 'put_user_inline'
   604 |                 if (node_updated && put_user_inline(node, naddr))
       |                                     ^~~~~~~~~~~~~~~
make[4]: *** [scripts/Makefile.build:289: kernel/futex/core.o] Error 1
make[3]: *** [scripts/Makefile.build:546: kernel/futex] Error 2
make[2]: *** [scripts/Makefile.build:546: kernel] Error 2
make[1]: *** [/home/chleroy/linux-powerpc/Makefile:2101: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2


> ---
>   include/linux/uaccess.h | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 64bc2492eb99..445391ec5a6d 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -739,7 +739,9 @@ static __always_inline void __scoped_user_rw_access_end(const void *p)
>   #define __scoped_user_access(mode, uptr, size, elbl)					\
>   	with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))	\
>   		/* Force modified pointer usage within the scope */			\
> -		and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr)
> +		__diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")	\
> +		and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
> +		__diag_pop()
>   
>   /**
>    * scoped_user_read_access_size - Start a scoped user read access with given size

Re: [PATCH v2 next 5/5] signal: Use scoped_user_access() instead of __put/get_user()

[Christophe Leroy (CS GROUP)]

Le 02/03/2026 à 14:27, david.laight.linux@gmail.com a écrit :
> From: David Laight <david.laight.linux@gmail.com>
> 
> Mechanically change the access_ok() and __get/put_user() to use
> scoped_user_read/write_access() and unsafe_get/put_user().
> 
> This generates better code with fewer STAC/CLAC pairs.
> 
> It also ensures that access_ok() is called near the user accesses.
> I failed to find the one for __save_altstack().

On arm64 it's done in get_sigframe() it seems.

> 
> Looking at the change, perhaps there should be aliases:
> #define scoped_put_user unsafe_put_user
> #define scoped_get_user unsafe_get_user

Might be confusing to have two macros doing exactly the same thing.

And the churn might be unnecessary on some code that already widely use 
unsafe_xxx macros and that we want to convert to scoped user access, 
like for instance arch/powerpc/kernel/signal_32.c

Christophe

Re: [PATCH v2 4/5] uaccess: Disable -Wshadow in __scoped_user_access()

[Linus Torvalds]

On Mon, 2 Mar 2026 at 05:28, <david.laight.linux@gmail.com> wrote:
>
> From: David Laight <david.laight.linux@gmail.com>
>
> -Wshadow is enabled by W=2 builds and __scoped_user_access() quite
> deliberately creates a 'const' shadow of the 'user' address that
> references a 'guard page' when the application passes a kernel pointer.

This is too ugly to live.

There is no way that we should make an already unreadable macro even
worse just because somebody - incorrectly - thinks that W=2 matters.

No - what matters a whole lot more is keeping the kernel sources
readable (well, at least as readable as is possible).

Because W=2 is one of those "you get what you deserve" things.

             Linus

Re: [PATCH v2 1/5] uaccess: Fix scoped_user_read_access() for 'pointer to const'

[Linus Torvalds]

On Mon, 2 Mar 2026 at 06:59, Christophe Leroy (CS GROUP)
<chleroy@kernel.org> wrote:
>
> Can we get this fix merged in 7.0-rc3 so that we can start building 7.1
> on top of it ?

Applied this first patch. I'm not so convinced about the others in the
series, although people can always try to argue for them..

              Linus

Re: [PATCH v2 1/5] uaccess: Fix scoped_user_read_access() for 'pointer to const'

[David Laight]

On Mon, 2 Mar 2026 09:26:31 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, 2 Mar 2026 at 06:59, Christophe Leroy (CS GROUP)
> <chleroy@kernel.org> wrote:
> >
> > Can we get this fix merged in 7.0-rc3 so that we can start building 7.1
> > on top of it ?  
> 
> Applied this first patch. I'm not so convinced about the others in the
> series, although people can always try to argue for them..

Patches 2 and 3 seemed a reasonable idea to me.
Removes a lot of code that is only there to make the whole thing work.
The 'with' is a bit of a take on Pascal - but without the 'making the
code completely unreadable' side effect.

I don't do WARN=1 builds, never mind WARN=2 :-)
Although -Wshadow can find real bugs - so I would turn it on and
suffer the annoyances. 

Patch 5 was just what I was experimenting with.
Doing the equivalent change to the non-compat version (IIRC it
uses the (likely) much slower copy_to/from_user() because the
structures match) might even be more sensible.

	David


> 
>               Linus

Re: [PATCH v2 4/5] uaccess: Disable -Wshadow in __scoped_user_access()

[David Laight]

On Mon, 2 Mar 2026 16:00:26 +0100
"Christophe Leroy (CS GROUP)" <chleroy@kernel.org> wrote:

> Le 02/03/2026 à 14:27, david.laight.linux@gmail.com a écrit :
> > From: David Laight <david.laight.linux@gmail.com>
> > 
> > -Wshadow is enabled by W=2 builds and __scoped_user_access() quite
> > deliberately creates a 'const' shadow of the 'user' address that
> > references a 'guard page' when the application passes a kernel pointer.
> > 
> > Signed-off-by: David Laight <david.laight.linux@gmail.com>  
> 
> There is a problem with this patch:

(badly line-wrapped errors deleted)

It seems to need gcc 12.
(So Linus is in luck.)

Prior to gcc 12 the #pragma generated by _Pragma() act as the
controlled statement of the for () loop.

Trying to put the _Pragma() inside the for statement doesn't work at all.

	David

Re: [PATCH v2 4/5] uaccess: Disable -Wshadow in __scoped_user_access()

[kernel test robot]

Hi,

kernel test robot noticed the following build errors:

[auto build test ERROR on brauner-vfs/vfs.all]
[also build test ERROR on v7.0-rc2]
[cannot apply to linus/master next-20260303]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/david-laight-linux-gmail-com/uaccess-Fix-scoped_user_read_access-for-pointer-to-const/20260302-213317
base:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.all
patch link:    https://lore.kernel.org/r/20260302132755.1475451-5-david.laight.linux%40gmail.com
patch subject: [PATCH v2 4/5] uaccess: Disable -Wshadow in __scoped_user_access()
config: nios2-allnoconfig (https://download.01.org/0day-ci/archive/20260305/202603051642.i46zzlJ8-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 11.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260305/202603051642.i46zzlJ8-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603051642.i46zzlJ8-lkp@intel.com/

All error/warnings (new ones prefixed by >>):

   In file included from include/asm-generic/div64.h:27,
                    from ./arch/nios2/include/generated/asm/div64.h:1,
                    from include/linux/math.h:6,
                    from include/linux/math64.h:6,
                    from include/linux/time.h:6,
                    from include/linux/compat.h:10,
                    from kernel/futex/core.c:34:
   kernel/futex/futex.h: In function 'futex_get_value_locked':
>> include/linux/uaccess.h:740:20: warning: unused variable '_tmpptr' [-Wunused-variable]
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |                    ^~~~~~~
   include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
     396 |         for (declaration; !_with_done; _with_done = true)
         |              ^~~~~~~~~~~
   include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |         ^~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
     288 |         return get_user_inline(*dest, from);
         |                ^~~~~~~~~~~~~~~
>> include/linux/compiler.h:396:9: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
     396 |         for (declaration; !_with_done; _with_done = true)
         |         ^~~
   include/linux/compiler.h:394:17: note: in expansion of macro 'and_with'
     394 |                 and_with (declaration)
         |                 ^~~~~~~~
   include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |         ^~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
     288 |         return get_user_inline(*dest, from);
         |                ^~~~~~~~~~~~~~~
   In file included from include/linux/compiler_types.h:173,
                    from <command-line>:
   include/linux/compiler-gcc.h:118:33: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
     118 | #define __diag(s)               _Pragma(__diag_str(GCC diagnostic s))
         |                                 ^~~~~~~
   include/linux/compiler-gcc.h:129:9: note: in expansion of macro '__diag'
     129 |         __diag(__diag_GCC_ignore option)
         |         ^~~~~~
   include/linux/uaccess.h:742:31: note: in expansion of macro '__diag_ignore_all'
     742 |                 __diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")    \
         |                               ^~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
     288 |         return get_user_inline(*dest, from);
         |                ^~~~~~~~~~~~~~~
   In file included from include/asm-generic/div64.h:27,
                    from ./arch/nios2/include/generated/asm/div64.h:1,
                    from include/linux/math.h:6,
                    from include/linux/math64.h:6,
                    from include/linux/time.h:6,
                    from include/linux/compat.h:10,
                    from kernel/futex/core.c:34:
>> include/linux/uaccess.h:743:90: error: '_tmpptr' undeclared (first use in this function)
     743 |                 and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
         |                                                                                          ^~~~~~~
   include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
     396 |         for (declaration; !_with_done; _with_done = true)
         |              ^~~~~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
     288 |         return get_user_inline(*dest, from);
         |                ^~~~~~~~~~~~~~~
   include/linux/uaccess.h:743:90: note: each undeclared identifier is reported only once for each function it appears in
     743 |                 and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
         |                                                                                          ^~~~~~~
   include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
     396 |         for (declaration; !_with_done; _with_done = true)
         |              ^~~~~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
     288 |         return get_user_inline(*dest, from);
         |                ^~~~~~~~~~~~~~~
>> include/linux/compiler.h:396:28: error: '_with_done' undeclared (first use in this function)
     396 |         for (declaration; !_with_done; _with_done = true)
         |                            ^~~~~~~~~~
   include/linux/uaccess.h:743:17: note: in expansion of macro 'and_with'
     743 |                 and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
         |                 ^~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/futex.h:288:16: note: in expansion of macro 'get_user_inline'
     288 |         return get_user_inline(*dest, from);
         |                ^~~~~~~~~~~~~~~
   kernel/futex/core.c: In function 'get_futex_key':
>> include/linux/uaccess.h:740:20: warning: unused variable '_tmpptr' [-Wunused-variable]
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |                    ^~~~~~~
   include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
     396 |         for (declaration; !_with_done; _with_done = true)
         |              ^~~~~~~~~~~
   include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |         ^~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
     584 |                 if (get_user_inline(node, naddr))
         |                     ^~~~~~~~~~~~~~~
>> include/linux/compiler.h:396:9: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
     396 |         for (declaration; !_with_done; _with_done = true)
         |         ^~~
   include/linux/compiler.h:394:17: note: in expansion of macro 'and_with'
     394 |                 and_with (declaration)
         |                 ^~~~~~~~
   include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |         ^~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
     584 |                 if (get_user_inline(node, naddr))
         |                     ^~~~~~~~~~~~~~~
   In file included from include/linux/compiler_types.h:173,
                    from <command-line>:
   include/linux/compiler-gcc.h:118:33: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
     118 | #define __diag(s)               _Pragma(__diag_str(GCC diagnostic s))
         |                                 ^~~~~~~
   include/linux/compiler-gcc.h:129:9: note: in expansion of macro '__diag'
     129 |         __diag(__diag_GCC_ignore option)
         |         ^~~~~~
   include/linux/uaccess.h:742:31: note: in expansion of macro '__diag_ignore_all'
     742 |                 __diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")    \
         |                               ^~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
     584 |                 if (get_user_inline(node, naddr))
         |                     ^~~~~~~~~~~~~~~
   In file included from include/asm-generic/div64.h:27,
                    from ./arch/nios2/include/generated/asm/div64.h:1,
                    from include/linux/math.h:6,
                    from include/linux/math64.h:6,
                    from include/linux/time.h:6,
                    from include/linux/compat.h:10,
                    from kernel/futex/core.c:34:
>> include/linux/uaccess.h:743:90: error: '_tmpptr' undeclared (first use in this function)
     743 |                 and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
         |                                                                                          ^~~~~~~
   include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
     396 |         for (declaration; !_with_done; _with_done = true)
         |              ^~~~~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
     584 |                 if (get_user_inline(node, naddr))
         |                     ^~~~~~~~~~~~~~~
>> include/linux/compiler.h:396:28: error: '_with_done' undeclared (first use in this function)
     396 |         for (declaration; !_with_done; _with_done = true)
         |                            ^~~~~~~~~~
   include/linux/uaccess.h:743:17: note: in expansion of macro 'and_with'
     743 |                 and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
         |                 ^~~~~~~~
   include/linux/uaccess.h:755:9: note: in expansion of macro '__scoped_user_access'
     755 |         __scoped_user_access(read, usrc, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:767:9: note: in expansion of macro 'scoped_user_read_access_size'
     767 |         scoped_user_read_access_size(usrc, sizeof(*(usrc)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:831:9: note: in expansion of macro 'scoped_user_read_access'
     831 |         scoped_user_read_access(_tmpsrc, efault)                \
         |         ^~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:584:21: note: in expansion of macro 'get_user_inline'
     584 |                 if (get_user_inline(node, naddr))
         |                     ^~~~~~~~~~~~~~~
>> include/linux/uaccess.h:740:20: warning: unused variable '_tmpptr' [-Wunused-variable]
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |                    ^~~~~~~
   include/linux/compiler.h:396:14: note: in definition of macro 'and_with'
     396 |         for (declaration; !_with_done; _with_done = true)
         |              ^~~~~~~~~~~
   include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |         ^~~~
   include/linux/uaccess.h:778:9: note: in expansion of macro '__scoped_user_access'
     778 |         __scoped_user_access(write, udst, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:790:9: note: in expansion of macro 'scoped_user_write_access_size'
     790 |         scoped_user_write_access_size(udst, sizeof(*(udst)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:856:9: note: in expansion of macro 'scoped_user_write_access'
     856 |         scoped_user_write_access(_tmpdst, efault)               \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:604:37: note: in expansion of macro 'put_user_inline'
     604 |                 if (node_updated && put_user_inline(node, naddr))
         |                                     ^~~~~~~~~~~~~~~
>> include/linux/compiler.h:396:9: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
     396 |         for (declaration; !_with_done; _with_done = true)
         |         ^~~
   include/linux/compiler.h:394:17: note: in expansion of macro 'and_with'
     394 |                 and_with (declaration)
         |                 ^~~~~~~~
   include/linux/uaccess.h:740:9: note: in expansion of macro 'with'
     740 |         with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))        \
         |         ^~~~
   include/linux/uaccess.h:778:9: note: in expansion of macro '__scoped_user_access'
     778 |         __scoped_user_access(write, udst, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:790:9: note: in expansion of macro 'scoped_user_write_access_size'
     790 |         scoped_user_write_access_size(udst, sizeof(*(udst)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:856:9: note: in expansion of macro 'scoped_user_write_access'
     856 |         scoped_user_write_access(_tmpdst, efault)               \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:604:37: note: in expansion of macro 'put_user_inline'
     604 |                 if (node_updated && put_user_inline(node, naddr))
         |                                     ^~~~~~~~~~~~~~~
   In file included from include/linux/compiler_types.h:173,
                    from <command-line>:
   include/linux/compiler-gcc.h:118:33: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'for'
     118 | #define __diag(s)               _Pragma(__diag_str(GCC diagnostic s))
         |                                 ^~~~~~~
   include/linux/compiler-gcc.h:129:9: note: in expansion of macro '__diag'
     129 |         __diag(__diag_GCC_ignore option)
         |         ^~~~~~
   include/linux/uaccess.h:742:31: note: in expansion of macro '__diag_ignore_all'
     742 |                 __diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")    \
         |                               ^~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:778:9: note: in expansion of macro '__scoped_user_access'
     778 |         __scoped_user_access(write, udst, size, elbl)
         |         ^~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:790:9: note: in expansion of macro 'scoped_user_write_access_size'
     790 |         scoped_user_write_access_size(udst, sizeof(*(udst)), elbl)
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/uaccess.h:856:9: note: in expansion of macro 'scoped_user_write_access'
     856 |         scoped_user_write_access(_tmpdst, efault)               \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~
   kernel/futex/core.c:604:37: note: in expansion of macro 'put_user_inline'
     604 |                 if (node_updated && put_user_inline(node, naddr))
         |                                     ^~~~~~~~~~~~~~~
..


vim +/_tmpptr +743 include/linux/uaccess.h

   689	
   690	/**
   691	 * __scoped_user_access - Open a scope for user access
   692	 * @mode:	The mode of the access class (read, write, rw)
   693	 * @uptr:	The pointer to access user space memory
   694	 * @size:	Size of the access
   695	 * @elbl:	Error label to goto when the access region is rejected. It
   696	 *		must be placed outside the scope
   697	 *
   698	 * If the user access function inside the scope requires a fault label, it
   699	 * can use @elbl or a different label outside the scope, which requires
   700	 * that user access which is implemented with ASM GOTO has been properly
   701	 * wrapped. See unsafe_get_user() for reference.
   702	 *
   703	 *	scoped_user_rw_access(ptr, efault) {
   704	 *		unsafe_get_user(rval, &ptr->rval, efault);
   705	 *		unsafe_put_user(wval, &ptr->wval, efault);
   706	 *	}
   707	 *	return 0;
   708	 *  efault:
   709	 *	return -EFAULT;
   710	 *
   711	 * The scope is internally implemented as a autoterminating nested for()
   712	 * loop, which can be left with 'return', 'break' and 'goto' at any
   713	 * point.
   714	 *
   715	 * When the scope is left user_##@_mode##_access_end() is automatically
   716	 * invoked.
   717	 *
   718	 * When the architecture supports masked user access and the access region
   719	 * which is determined by @uptr and @size is not a valid user space
   720	 * address, i.e. < TASK_SIZE, the scope sets the pointer to a faulting user
   721	 * space address and does not terminate early. This optimizes for the good
   722	 * case and lets the performance uncritical bad case go through the fault.
   723	 *
   724	 * The eventual modification of the pointer is limited to the scope.
   725	 * Outside of the scope the original pointer value is unmodified, so that
   726	 * the original pointer value is available for diagnostic purposes in an
   727	 * out of scope fault path.
   728	 *
   729	 * Nesting scoped user access into a user access scope is invalid and fails
   730	 * the build. Nesting into other guards, e.g. pagefault is safe.
   731	 *
   732	 * The masked variant does not check the size of the access and relies on a
   733	 * mapping hole (e.g. guard page) to catch an out of range pointer, the
   734	 * first access to user memory inside the scope has to be within
   735	 * @uptr ... @uptr + PAGE_SIZE - 1
   736	 *
   737	 * Don't use directly. Use scoped_masked_user_$MODE_access() instead.
   738	 */
   739	#define __scoped_user_access(mode, uptr, size, elbl)					\
 > 740		with (auto _tmpptr = __scoped_user_access_begin(mode, uptr, size, elbl))	\
   741			/* Force modified pointer usage within the scope */			\
   742			__diag_push() __diag_ignore_all("-Wshadow", "uptr is readonly copy")	\
 > 743			and_with (const auto uptr __cleanup(__scoped_user_##mode##_access_end) = _tmpptr) \
   744			__diag_pop()
   745	

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