Re: [PATCHv5 05/13] x86/uaccess: Provide untagged_addr() and remove tags before address check

[Alexander Potapenko]

On Wed, Jul 13, 2022 at 1:13 AM Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> untagged_addr() is a helper used by the core-mm to strip tag bits and
> get the address to the canonical shape. In only handles userspace
> addresses. The untagging mask is stored in mmu_context and will be set
> on enabling LAM for the process.
>
> The tags must not be included into check whether it's okay to access the
> userspace address.
>
> Strip tags in access_ok().
>
> get_user() and put_user() don't use access_ok(), but check access
> against TASK_SIZE directly in assembly. Strip tags, before calling into
> the assembly helper.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Tested-by: Alexander Potapenko <glider@xxxxxxxxxx>