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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 2 Apr 2019 14:47:34 +0200
Message-ID: <CAAeHK+xe-zWn8WpCxUxBB2tXL8oiLkshkPi1J3Ly87mACaA4-A@mail.gmail.com>
Subject: Re: [PATCH v13 04/20] mm, arm64: untag user pointers passed to memory syscalls
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Eric Dumazet <edumazet@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Jens Wiklander <jens.wiklander@linaro.org>,
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        Dmitry Vyukov <dvyukov@google.com>,
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On Fri, Mar 29, 2019 at 11:30 AM Catalin Marinas
<catalin.marinas@arm.com> wrote:
>
> (I trimmed down the cc list a bit since it's always bouncing)
>
> 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.

>
> (I had a hack overriding __SC_CAST to do this automatically for pointer
> arguments but this wouldn't work on mmap() and friends as the argument
> is unsigned long)
>
> --
> Catalin