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

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Date:   Mon, 2 Jul 2018 15:00:15 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. 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 <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        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: validate rseq_cs fields are <
 TASK_SIZE

----- On Jul 2, 2018, at 1:11 PM, Andy Lutomirski luto@...capital.net wrote:
> 
> But I think that the limited solution of changing
> instruction_pointer_set() really is a sufficient
> architecture-dependent change to fully solve your problem.

So let me recap with the changes I gather for 4.18 and 4.19:

4.18:

* Change struct rseq_cs field types from LINUX_FIELD_u32_u64() to __u64 in
  uapi/linux/rseq.h,
* Compare rseq->rseq_cs->abort_ip with TASK_SIZE before using it. Kill offending
  process if its value is over TASK_SIZE,
* Explicitly check that padding of rseq->rseq_cs is zero on 32-bit kernels
  (#ifndef __LP64__).

4.19:

* Introduce instruction_pointer_set() with input validation, use it when setting
  IP to abort_ip in rseq. This replaces the comparison of abort_ip with TASK_SIZE.

Is that consistent with what you have in mind ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com