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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 28 Jun 2018 14:22:27 -0700
Message-ID: <CA+55aFxZrv9koOGKNzpBjcpzwaKQBg9ybqcvQ9u=5d94y1F+mQ@mail.gmail.com>
Subject: Re: [RFC PATCH for 4.18 1/2] rseq: validate rseq_cs fields are < TASK_SIZE
To:     Andrew Lutomirski <luto@kernel.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        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>,
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        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>, joelaf@google.com
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On Thu, Jun 28, 2018 at 1:23 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> This is okay with me for a fix outside the merge window.  Can you do a
> followup for the next merge window that fixes it better, though?  In
> particular, TASK_SIZE is generally garbage.  I think a better fix
> would be something like adding a new arch-overridable helper like:
>
> static inline unsigned long current_max_user_addr(void) { return TASK_SIZE; }

We already have that. It's called "user_addr_max()".

It's the limit we use for user accesses.

That said, I don't see why we should even check the IP. It's not like
that's done by signal handling either.

                     Linus