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

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Message-ID: <1578770214.71411.1618324461988.JavaMail.zimbra@efficios.com>
Date:   Tue, 13 Apr 2021 10:34:21 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     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>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH 2/3] rseq: remove redundant access_ok()

----- 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.

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