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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 28 Jun 2018 17:18:22 -0700
Message-ID: <CA+55aFzxCjkSbfRUeX3W_oXSJ6LMUdRVYB=DR2b3rUNkiixM1A@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>,
        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>, joelaf@google.com
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On Thu, Jun 28, 2018 at 4:30 PM Andy Lutomirski <luto@kernel.org> wrote:
>
> The idea is that, if someone screws up and sticks a number like
> 0xbaadf00d00045678 into their rseq abort_ip in a 32-bit x86 program
> (when they actually mean 0x00045678), we want to something consistent.

I think the "something consistent" is perfectly fine with just "it won't work".

Make it do

        if (rseq_cs->abort_ip != (unsigned long)rseq_cs->abort_ip)
                return -EINVAL;

at abort time.

Done.

If it's a 32-bit kernel, the above will reject the thing, and if it's
a 64-bit kernel, it will be a no-op, but the abort won't work in a
32-bit caller.

Problem solved.

             Linus