linux-kernel - Re: [RFC PATCH for 4.18 1/2] rseq: use __u64 for rseq_cs fields, validate abort_ip < TASK

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Date:   Mon, 2 Jul 2018 15:08:42 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     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>,
        Andy Lutomirski <luto@...capital.net>,
        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>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.18 1/2] rseq: use __u64 for rseq_cs fields,
 validate abort_ip < TASK_SIZE

On Mon, Jul 2, 2018 at 3:03 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
>         if (__get_user(ptr, &t->rseq->rseq_cs))
>                 return -EINVAL;
>         if (check_rseq_cs_padding(t))
>                 return -EINVAL;

Small nit.

I think the _actual_ user access faults should return -EFAULT, and
then the *validation* checks should return -EINVAL.

So when the "copy_from_user()" fails, that's -EFAULT, but when you
have (rseq_cs->start_ip >= TASK_SIZE), that's -EINVAL.

That said, nothing actually cares or exposes the error number, I
think. Afaik, all the callers just check "did it work" or not.

So this is more a "let's be consistent" than anything that matters.

             Linus