linux-kernel - Re: [PATCH 10/18] qla2xxx: prevent bounds-check bypass via speculative execution

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Message-ID: <CAPcyv4jQjwa5X6ctO7bU1Z3hfRGRTa6gDO3pSSo_HQHkjg4MFg@mail.gmail.com>
Date:   Thu, 11 Jan 2018 14:15:12 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch@...r.kernel.org,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Netdev <netdev@...r.kernel.org>, qla2xxx-upstream@...gic.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH 10/18] qla2xxx: prevent bounds-check bypass via
 speculative execution

On Sat, Jan 6, 2018 at 1:03 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Jan 05, 2018 at 05:10:48PM -0800, Dan Williams wrote:
>> Static analysis reports that 'handle' may be a user controlled value
>> that is used as a data dependency to read 'sp' from the
>> 'req->outstanding_cmds' array.  In order to avoid potential leaks of
>> kernel memory values, block speculative execution of the instruction
>> stream that could issue reads based on an invalid value of 'sp'. In this
>> case 'sp' is directly dereferenced later in the function.
>
> I'm pretty sure that 'handle' comes from the hardware, not from
> userspace, from what I can tell here.  If we want to start auditing
> __iomem data sources, great!  But that's a bigger task, and one I don't
> think we are ready to tackle...

I think it falls in the hygiene bucket of shutting off an array index
from a source that could be under attacker control. Should we leave
this one un-patched while we decide if we generally have a problem
with trusting completion 'tags' from hardware? My vote is patch it for
now.