linux-kernel - Re: [PATCH net] net: fman: Use physical address for userspace interfaces

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Date:   Tue, 18 Oct 2022 13:33:55 -0500
From:   Andrew Davis <afd@...com>
To:     Sean Anderson <sean.anderson@...o.com>,
        Andrew Lunn <andrew@...n.ch>
CC:     "David S . Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Madalin Bucur <madalin.bucur@....com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Camelia Groza <camelia.groza@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH net] net: fman: Use physical address for userspace
 interfaces

On 10/18/22 12:37 PM, Sean Anderson wrote:
> Hi Andrew,
> 
> On 10/18/22 1:22 PM, Andrew Lunn wrote:
>> On Mon, Oct 17, 2022 at 12:28:06PM -0400, Sean Anderson wrote:
>>> For whatever reason, the address of the MAC is exposed to userspace in
>>> several places. We need to use the physical address for this purpose to
>>> avoid leaking information about the kernel's memory layout, and to keep
>>> backwards compatibility.
>>
>> How does this keep backwards compatibility? Whatever is in user space
>> using this virtual address expects a virtual address. If it now gets a
>> physical address it will probably do the wrong thing. Unless there is
>> a one to one mapping, and you are exposing virtual addresses anyway.
>>
>> If you are going to break backwards compatibility Maybe it would be
>> better to return 0xdeadbeef? Or 0?
>>
>>         Andrew
>>
> 
> The fixed commit was added in v6.1-rc1 and switched from physical to
> virtual. So this is effectively a partial revert to the previous
> behavior (but keeping the other changes). See [1] for discussion.
> 
> --Sean
> 
> [1] https://lore.kernel.org/netdev/20220902215737.981341-1-sean.anderson@seco.com/T/#md5c6b66bc229c09062d205352a7d127c02b8d262

I see it asked in that thread, but not answered. Why are you exposing
"physical" addresses to userspace? There should be no reason for that.

Andrew