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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 2 Jul 2018 19:44:23 -0700
Message-ID: <CA+55aFytFfjRSdWapQ0F6RjuFgy9oSHjMtFpDPwAh4G9QRfUNw@mail.gmail.com>
Subject: Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate
 user inputs
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Dave Watson <davejwatson@fb.com>, Paul Turner <pjt@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Ingo Molnar <mingo@redhat.com>, Peter Anvin <hpa@zytor.com>,
        Andi Kleen <andi@firstfloor.org>,
        Christoph Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
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On Mon, Jul 2, 2018 at 7:30 PM Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
>
> Is it really ? Last time we had this discussion, not all architectures
> guaranteed that reading a 64-bit integer would happen in two atomic
> 32-bit sub-parts.

All architectures that matter do.

Please don't overdesign this, or try to make a problem out of
something that isn't a problem.

Sure, maybe some toy architecture does a 8-byte "get_user()" as a
"copy_from_user()" one byte at a time, because that's the best way to
do unaligned accesses.

But nobody will ever care about rseq on such a thing anyway. Let it go.

               Linus