[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 at gmail.com a écrit :
> From: David Laight <david.laight.linux at 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 at gmail.com>

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