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

[Sean Anderson]

On 10/19/22 02:46, Geert Uytterhoeven wrote:
> Hi Madalin,
>
> On Wed, Oct 19, 2022 at 7:20 AM Madalin Bucur <madalin.bucur@xxxxxxx> wrote:
> > > -----Original Message-----
> > > From: Sean Anderson <sean.anderson@xxxxxxxx>
> > > Sent: 19 October 2022 00:47
> > > To: Andrew Lunn <andrew@xxxxxxx>; Andrew Davis <afd@xxxxxx>
> > > Cc: David S . Miller <davem@xxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx;
> > > linux-kernel@xxxxxxxxxxxxxxx; Madalin Bucur <madalin.bucur@xxxxxxx>;
> > > Jakub Kicinski <kuba@xxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>;
> > > Paolo Abeni <pabeni@xxxxxxxxxx>; Camelia Alexandra Groza
> > > <camelia.groza@xxxxxxx>; Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > > Subject: Re: [PATCH net] net: fman: Use physical address for userspace
> > > interfaces
> > >
> > >
> > >
> > > On 10/18/22 5:39 PM, Andrew Lunn wrote:
> > > > On Tue, Oct 18, 2022 at 01:33:55PM -0500, Andrew Davis wrote:
> > > > > 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.
> > > >
> > > > Please don't assume a reviewer has seen the previous
> > > > discussion. Include the background in the commit message to help such
> > > > reviewers.
>
> > > > > 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.
> > > >
> > > > I don't see anything about needing physical or virtual address in the
> > > > discussion, or i've missed it.
> > >
> > > Well, Madalin originally added this, so perhaps she has some insight.
> > >
> > > I have no idea why we set the IFMAP stuff, since that seems like it's for
> > > PCMCIA. Not sure about sysfs either.
> > >
> > > > If nobody knows why it is needed, either use an obfusticated value, or
> > > > remove it all together. If somebody/something does need it, they will
> > > > report the regression.
> > >
> > > I'd rather apply this (or v2 of this) and then remove the "feature" in
> > > follow-up.
> > >
> > > --Sean
> >
> >
> > root@localhost:~# grep 1ae /etc/udev/rules.d/72-fsl-dpaa-persistent-networking.rules
> > SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae0000", NAME="fm1-mac1"
> > SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae2000", NAME="fm1-mac2"
> > SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae4000", NAME="fm1-mac3"
> > SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae6000", NAME="fm1-mac4"
> > SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae8000", NAME="fm1-mac5"
> > SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1aea000", NAME="fm1-mac6"
>
> So you rely on the physical address.
> It's a pity this uses a custom sysfs file.
> Can't you obtain this information some other way?
> Anyway, as this is in use, it became part of the ABI.

In my udev rules I use ID_PATH. Since this is a devicetree platform, the path name includes
the device address by convention.

--Sean

> > root@localhost:~# grep 1ae  /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@*/net/fm1-mac*/device_addr
> > /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@2/net/fm1-mac3/device_addr:1ae4000
> > /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@3/net/fm1-mac4/device_addr:1ae6000
> > /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@4/net/fm1-mac5/device_addr:1ae8000
> > /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@5/net/fm1-mac6/device_addr:1aea000
>
>
> Gr{oetje,eeting}s,
>
>                          Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds