linux-kernel - Re: [PATCH 2/3] rseq: remove redundant access

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Message-ID: <CANn89i+8NPFwqVANzdYNmiSgsJ3fUL7Sk4akJUk1zpnKR5B-mQ@mail.gmail.com>
Date:   Tue, 13 Apr 2021 17:19:36 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Arjun Roy <arjunroy@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] rseq: remove redundant access_ok()

On Tue, Apr 13, 2021 at 4:34 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> ----- On Apr 13, 2021, at 3:36 AM, Eric Dumazet eric.dumazet@...il.com wrote:
>
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > After commit 8f2817701492 ("rseq: Use get_user/put_user rather
> > than __get_user/__put_user") we no longer need
> > an access_ok() call from __rseq_handle_notify_resume()
>
> While we are doing that, should we also remove the access_ok() check in
> rseq_syscall() ? It look like it can also be removed for the exact same
> reason outlined here.

Yes, good idea.

 I was focusing in __rseq_handle_notify_resume() paths but
rseq_syscall() can get the same.

> Thanks,
>
> Mathieu
>
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Arjun Roy <arjunroy@...gle.com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > ---
> > kernel/rseq.c | 2 --
> > 1 file changed, 2 deletions(-)
> >
> > diff --git a/kernel/rseq.c b/kernel/rseq.c
> > index
> > d2689ccbb132c0fc8ec0924008771e5ee1ca855e..57344f9abb43905c7dd2b6081205ff508d963e1e
> > 100644
> > --- a/kernel/rseq.c
> > +++ b/kernel/rseq.c
> > @@ -273,8 +273,6 @@ void __rseq_handle_notify_resume(struct ksignal *ksig,
> > struct pt_regs *regs)
> >
> >       if (unlikely(t->flags & PF_EXITING))
> >               return;
> > -     if (unlikely(!access_ok(t->rseq, sizeof(*t->rseq))))
> > -             goto error;
> >       ret = rseq_ip_fixup(regs);
> >       if (unlikely(ret < 0))
> >               goto error;
> > --
> > 2.31.1.295.g9ea45b61b8-goog
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com