Re: [PATCH v13 04/20] mm, arm64: untag user pointers passed to memory syscalls

[Catalin Marinas <catalin.marinas@arm.com>]

On Tue, Apr 02, 2019 at 02:47:34PM +0200, Andrey Konovalov wrote:
> On Fri, Mar 29, 2019 at 11:30 AM Catalin Marinas
> <catalin.marinas@arm.com> wrote:
> > On Thu, Mar 28, 2019 at 02:19:34PM -0400, Steven Rostedt wrote:
> > > On Thu, 28 Mar 2019 19:10:07 +0100
> > > Andrey Konovalov <andreyknvl@google.com> wrote:
> > >
> > > > > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> > > > > > ---
> > > > > >  ipc/shm.c      | 2 ++
> > > > > >  mm/madvise.c   | 2 ++
> > > > > >  mm/mempolicy.c | 5 +++++
> > > > > >  mm/migrate.c   | 1 +
> > > > > >  mm/mincore.c   | 2 ++
> > > > > >  mm/mlock.c     | 5 +++++
> > > > > >  mm/mmap.c      | 7 +++++++
> > > > > >  mm/mprotect.c  | 1 +
> > > > > >  mm/mremap.c    | 2 ++
> > > > > >  mm/msync.c     | 2 ++
> > > > > >  10 files changed, 29 insertions(+)
> > > > >
> > > > > I wonder whether it's better to keep these as wrappers in the arm64
> > > > > code.
> > > >
> > > > I don't think I understand what you propose, could you elaborate?
> > >
> > > I believe Catalin is saying that instead of placing things like:
> > >
> > > @@ -1593,6 +1593,7 @@ SYSCALL_DEFINE3(shmat, int, shmid, char __user *, shmaddr, int, shmflg)
> > >       unsigned long ret;
> > >       long err;
> > >
> > > +     shmaddr = untagged_addr(shmaddr);
> > >
> > > To instead have the shmaddr set to the untagged_addr() before calling
> > > the system call, and passing the untagged addr to the system call, as
> > > that goes through the arm64 architecture specific code first.
> >
> > Indeed. For example, we already have a SYSCALL_DEFINE6(mmap, ...) in
> > arch/arm64/kernel/sys.c, just add the untagging there. We could do
> > something similar for the other syscalls. I don't mind doing this in the
> > generic code but if it's only needed for arm64, I'd rather keep the
> > generic changes to a minimum.
> 
> Do I understand correctly, that I'll need to add ksys_ wrappers for
> each of the memory syscalls, and then redefine them in
> arch/arm64/kernel/sys.c with arm64_ prefix, like it is done for the
> personality syscall right now? This will require generic changes as
> well.

Yes. My aim is to keep the number of untagged_addr() calls in the
generic code to a minimum (rather than just keeping the generic code
changes small).

-- 
Catalin