memfd_secret: use unsigned int rather than long as syscall flags type

From: Mike Rapoport <rppt@linux.ibm.com>

Yuri Norov says:

  If parameter size is the same for native and compat ABIs, we may
  wire a syscall made by compat client to native handler. This is
  true for unsigned int, but not true for unsigned long or pointer.

  That's why I suggest using unsigned int and so avoid creating compat
  entry point.

Use unsigned int as the type of the flags parameter in memfd_secret()
system call.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---

@Andrew,
The patch is vs v5.12-rc5-mmots-2021-03-30-23, I'd appreciate if it would
be added as a fixup to the memfd_secret series.

 include/linux/syscalls.h                  | 2 +-
 mm/secretmem.c                            | 2 +-
 tools/testing/selftests/vm/memfd_secret.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

On 31.03.21 16:23, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Yuri Norov says:
> 
>    If parameter size is the same for native and compat ABIs, we may
>    wire a syscall made by compat client to native handler. This is
>    true for unsigned int, but not true for unsigned long or pointer.
> 
>    That's why I suggest using unsigned int and so avoid creating compat
>    entry point.
> 
> Use unsigned int as the type of the flags parameter in memfd_secret()
> system call.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> 
> @Andrew,
> The patch is vs v5.12-rc5-mmots-2021-03-30-23, I'd appreciate if it would
> be added as a fixup to the memfd_secret series.
> 
>   include/linux/syscalls.h                  | 2 +-
>   mm/secretmem.c                            | 2 +-
>   tools/testing/selftests/vm/memfd_secret.c | 2 +-
>   3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 49c93c906893..1a1b5d724497 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -1050,7 +1050,7 @@ asmlinkage long sys_landlock_create_ruleset(const struct landlock_ruleset_attr _
>   asmlinkage long sys_landlock_add_rule(int ruleset_fd, enum landlock_rule_type rule_type,
>   		const void __user *rule_attr, __u32 flags);
>   asmlinkage long sys_landlock_restrict_self(int ruleset_fd, __u32 flags);
> -asmlinkage long sys_memfd_secret(unsigned long flags);
> +asmlinkage long sys_memfd_secret(unsigned int flags);
>   
>   /*
>    * Architecture-specific system calls
> diff --git a/mm/secretmem.c b/mm/secretmem.c
> index f2ae3f32a193..3b1ba3991964 100644
> --- a/mm/secretmem.c
> +++ b/mm/secretmem.c
> @@ -199,7 +199,7 @@ static struct file *secretmem_file_create(unsigned long flags)
>   	return file;
>   }
>   
> -SYSCALL_DEFINE1(memfd_secret, unsigned long, flags)
> +SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
>   {
>   	struct file *file;
>   	int fd, err;
> diff --git a/tools/testing/selftests/vm/memfd_secret.c b/tools/testing/selftests/vm/memfd_secret.c
> index c878c2b841fc..2462f52e9c96 100644
> --- a/tools/testing/selftests/vm/memfd_secret.c
> +++ b/tools/testing/selftests/vm/memfd_secret.c
> @@ -38,7 +38,7 @@ static unsigned long page_size;
>   static unsigned long mlock_limit_cur;
>   static unsigned long mlock_limit_max;
>   
> -static int memfd_secret(unsigned long flags)
> +static int memfd_secret(unsigned int flags)
>   {
>   	return syscall(__NR_memfd_secret, flags);
>   }
> 

LGTM

On Wed, Mar 31, 2021 at 05:23:45PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Yuri Norov says:
> 
>   If parameter size is the same for native and compat ABIs, we may
>   wire a syscall made by compat client to native handler. This is
>   true for unsigned int, but not true for unsigned long or pointer.
> 
>   That's why I suggest using unsigned int and so avoid creating compat
>   entry point.
> 
> Use unsigned int as the type of the flags parameter in memfd_secret()
> system call.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>

Acked-by: Yury Norov <yury.norov@gmail.com>