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Subject: Re: [PATCH net] net: fman: Use physical address for userspace
 interfaces
To:     Andrew Lunn <andrew@lunn.ch>
Cc:     "David S . Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Madalin Bucur <madalin.bucur@nxp.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Camelia Groza <camelia.groza@nxp.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>
References: <20221017162807.1692691-1-sean.anderson@seco.com>
 <Y07guYuGySM6F/us@lunn.ch>
From:   Sean Anderson <sean.anderson@seco.com>
Message-ID: <c409789a-68cb-7aba-af31-31488b16f918@seco.com>
Date:   Tue, 18 Oct 2022 13:37:27 -0400
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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