linux-kernel - Re: [PATCH 05/20] x86/uaccess/xen: Suppress SMAP warnings

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Message-ID: <b1e10fc1-e3cd-b3ad-0a87-3e486d0bce21@suse.com>
Date:   Thu, 7 Mar 2019 13:36:29 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, jpoimboe@...hat.com,
        luto@...nel.org, bp@...en8.de, dvlasenk@...hat.com,
        linux-kernel@...r.kernel.org, dvyukov@...gle.com,
        rostedt@...dmis.org, andrew.cooper3@...rix.com,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH 05/20] x86/uaccess/xen: Suppress SMAP warnings

On 07/03/2019 13:32, Peter Zijlstra wrote:
> On Thu, Mar 07, 2019 at 01:22:52PM +0100, Juergen Gross wrote:
>> On 07/03/2019 12:45, Peter Zijlstra wrote:
>>> drivers/xen/privcmd.o: warning: objtool: privcmd_ioctl()+0x1414: call to hypercall_page() with UACCESS enabled
>>>
>>> Xen needs to do HV calls with AC=1 for hysterical raisins. Make the
>>> warning go away.
>>
>> No, this is a hypercall with parameters passed through from user land
>> (Xen tools). So setting AC=1 is not related to hysterical reasons, but
>> to indicate that unprivileged buffers are okay here. So please change
>> the commit message to something like:
>>
>> Some Xen hypercalls allow parameter buffers in user land, so they need
>> to set AC=1. Avoid the warning for those cases.
> 
> *yuck* that's gross...
> 
> And I understood from Andrew yesterday (but perhaps I misunderstood)
> that the whole privcmd thing was a bit of a hack.

That was an unwise design decision in the past, yes. Changing it will
require a lot of effort.

> But sure, I'll change the message.

Thanks. :-)


Juergen