linux-kernel - Re: [RFC PATCH for 4.18 1/2] rseq: validate rseq_cs fields are < TASK

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Date:   Thu, 28 Jun 2018 14:22:27 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrew Lutomirski <luto@...nel.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>,
        Andi Kleen <andi@...stfloor.org>,
        Christoph Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>, joelaf@...gle.com
Subject: Re: [RFC PATCH for 4.18 1/2] rseq: validate rseq_cs fields are < TASK_SIZE

On Thu, Jun 28, 2018 at 1:23 PM Andy Lutomirski <luto@...nel.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