Re: [PATCH 1/5] uaccess: Add masked_user_{read/write}_access_begin

David Laight
2025-06-22T16:35:58Z

On Sun, 22 Jun 2025 11:52:39 +0200
Christophe Leroy <christophe.leroy@csgroup.eu> wrote:

> Allthough masked_user_access_begin() seems to only be used when reading
> data from user at the moment, introduce masked_user_read_access_begin()
> and masked_user_write_access_begin() in order to match
> user_read_access_begin() and user_write_access_begin().
>
> Have them default to masked_user_access_begin() when they are
> not defined.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> fs/select.c | 2 +-
> include/linux/uaccess.h | 8 ++++++++
> kernel/futex/futex.h | 4 ++--
> lib/strncpy_from_user.c | 2 +-
> lib/strnlen_user.c | 2 +-
> 5 files changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/fs/select.c b/fs/select.c
> index 9fb650d03d52..d8547bedf5eb 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -777,7 +777,7 @@ static inline int get_sigset_argpack(struct sigset_argpack *to,
> // the path is hot enough for overhead of copy_from_user() to matter
> if (from) {
> if (can_do_masked_user_access())
> - from = masked_user_access_begin(from);
> + from = masked_user_read_access_begin(from);
> else if (!user_read_access_begin(from, sizeof(*from)))
> return -EFAULT;
> unsafe_get_user(to->p, &from->p, Efault);
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 7c06f4795670..682a0cd2fe51 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -41,6 +41,14 @@

> #ifdef masked_user_access_begin
> #define can_do_masked_user_access() 1
> #else
> #define can_do_masked_user_access() 0
> #define masked_user_access_begin(src) NULL
> #define mask_user_address(src) (src)
> #endif
>
> +#ifndef masked_user_write_access_begin
> +#define masked_user_write_access_begin masked_user_access_begin
> +#endif
> +#ifndef masked_user_read_access_begin
> +#define masked_user_read_access_begin masked_user_access_begin
> +#endif

I think that needs merging with the bit above.
Perhaps generating something like:

#ifdef masked_user_access_begin
#define masked_user_read_access_begin masked_user_access_begin
#define masked_user_write_access_begin masked_user_access_begin
#endif

#ifdef masked_user_read_access_begin
#define can_do_masked_user_access() 1
#else
#define can_do_masked_user_access() 0
#define masked_user_read_access_begin(src) NULL
#define masked_user_write_access_begin(src) NULL
#define mask_user_address(src) (src)
#endif

Otherwise you'll have to #define masked_user_access_begin even though
it is never used.

Two more patches could change x86-64 to define both and then remove
the 'then unused' first check - but that has to be for later.

David