Re: [PATCH v16 08/16] fs, arm64: untag user pointers in copy_mount_options

Andrey Konovalov
2019-06-12T11:36:59Z

On Tue, Jun 11, 2019 at 4:38 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> On Sat, Jun 8, 2019 at 6:02 AM Kees Cook <keescook@chromium.org> wrote:
> >
> > On Mon, Jun 03, 2019 at 06:55:10PM +0200, Andrey Konovalov wrote:
> > > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > > pass tagged user pointers (with the top byte set to something else other
> > > than 0x00) as syscall arguments.
> > >
> > > In copy_mount_options a user address is being subtracted from TASK_SIZE.
> > > If the address is lower than TASK_SIZE, the size is calculated to not
> > > allow the exact_copy_from_user() call to cross TASK_SIZE boundary.
> > > However if the address is tagged, then the size will be calculated
> > > incorrectly.
> > >
> > > Untag the address before subtracting.
> > >
> > > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> >
> > One thing I just noticed in the commit titles... "arm64" is in the
> > prefix, but these are arch-indep areas. Should the ", arm64" be left
> > out?
> >
> > I would expect, instead:
> >
> > fs/namespace: untag user pointers in copy_mount_options
>
> Hm, I've added the arm64 tag in all of the patches because they are
> related to changes in arm64 kernel ABI. I can remove it from all the
> patches that only touch common code if you think that it makes sense.

I'll keep the arm64 tags in commit titles for v17. Please reply
explicitly if you think I should remove them. Thanks! :)

>
> Thanks!
>
> >
> > Reviewed-by: Kees Cook <keescook@chromium.org>
> >
> > -Kees
> >
> > > ---
> > > fs/namespace.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/fs/namespace.c b/fs/namespace.c
> > > index b26778bdc236..2e85712a19ed 100644
> > > --- a/fs/namespace.c
> > > +++ b/fs/namespace.c
> > > @@ -2993,7 +2993,7 @@ void *copy_mount_options(const void __user * data)
> > > * the remainder of the page.
> > > */
> > > /* copy_from_user cannot cross TASK_SIZE ! */
> > > - size = TASK_SIZE - (unsigned long)data;
> > > + size = TASK_SIZE - (unsigned long)untagged_addr(data);
> > > if (size > PAGE_SIZE)
> > > size = PAGE_SIZE;
> > >
> > > --
> > > 2.22.0.rc1.311.g5d7573a151-goog
> > >
> >
> > --
> > Kees Cook