linux-kernel - Re: [PATCH v3] of: overlay: user space synchronization

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Date:   Fri, 19 Oct 2018 09:08:53 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Rob Herring <robh@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Pantelis Antoniou <panto@...oniou-consulting.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alan Tull <atull@...nel.org>
Subject: Re: [PATCH v3] of: overlay: user space synchronization

Hi Frank,

On Fri, Oct 19, 2018 at 2:06 AM Frank Rowand <frowand.list@...il.com> wrote:
> On 10/18/18 12:32, Rob Herring wrote:
> > On Tue, Oct 16, 2018 at 05:34:26PM -0700, frowand.list@...il.com wrote:
> >> Provide a sysfs file, /sys/firmware/devicetree/tree_version,  to allow
> >> user space to determine if the live devicetree has remained unchanged
> >> while a series of one or more accesses of /proc/device-tree/ occur.
> >>
> >> The use of both (1) dynamic devicetree modifications and (2) overlay
> >> apply and removal are not supported during the same boot cycle.  Thus
> >> non-overlay dynamic modifications are not reflected in the value of
> >> tree_version.
> >
> > I'd prefer to see some sort of information on overlays exported and user
> > space can check if that changed. IIRC, Pantelis had a series to do that
> > along with a kill switch to prevent further modifications. At least some
> > of that series only had minor issues to fix.
>
> The kill switch addresses a different concern, which was from the security
> community.  The kill switch is on my todo list.
>
> I don't remember exactly what info the overlay information export patch
> provided.  I'll have to go find it and re-read it.

I'm still forward porting the overlay configfs interface, cfr.
https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/log/?h=topic/renesas-overlays

E.g. after loading r8a7791-koelsch-exio-b-scifa3.dtbo, it changes like:

--- tree /sys/firmware/devicetree old 2018-10-19 08:49:24.073441000 +0200
+++ tree /sys/firmware/devicetree new 2018-10-19 08:49:33.173397000 +0200
@@ -1237,6 +1237,11 @@
 │   │   │   │   ├── groups
 │   │   │   │   ├── name
 │   │   │   │   └── phandle
+│   │   │   ├── scifa3
+│   │   │   │   ├── function
+│   │   │   │   ├── groups
+│   │   │   │   ├── name
+│   │   │   │   └── phandle
 │   │   │   ├── scif_clk
 │   │   │   │   ├── function
 │   │   │   │   ├── groups
@@ -1510,6 +1515,8 @@
 │   │   │   ├── interrupts
 │   │   │   ├── name
 │   │   │   ├── phandle
+│   │   │   ├── pinctrl-0
+│   │   │   ├── pinctrl-names
 │   │   │   ├── power-domains
 │   │   │   ├── reg
 │   │   │   ├── resets
@@ -2277,6 +2284,7 @@
 │   │   ├── scifa1
 │   │   ├── scifa2
 │   │   ├── scifa3
+│   │   ├── scifa3_pins
 │   │   ├── scifa4
 │   │   ├── scifa5
 │   │   ├── scifb0

The above hunks are for /sys/firmware/devicetree/base/.

@@ -2778,6 +2786,14 @@
     │   │   └── target
     │   └── __symbols__
     │       └── target
+    ├── 2
+    │   ├── can_remove
+    │   ├── fragment@0
+    │   │   └── target
+    │   ├── fragment@1
+    │   │   └── target
+    │   └── __symbols__
+    │       └── target
     └── enable

The above hunk is for /sys/firmware/devicetree/overlays/

# ls -l /sys/firmware/devicetree/overlays/
total 0
drwxr-xr-x 6 root root    0 okt 19 08:49 1
drwxr-xr-x 5 root root    0 okt 19 08:49 2
-rw-r--r-- 1 root root 4096 okt 19 08:49 enable

1 is from the DT unit tests,
2 is from r8a7791-koelsch-exio-b-scifa3.dtbo,
enable is the kill switch.

Note that after removing overlay 2, and loading a new overlay, the new one is
again called number 2.  But the subdir date is newer.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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