Date:   Mon, 15 Oct 2018 14:01:15 -0500
From:   Alan Tull <atull@...nel.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Moritz Fischer <mdf@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, linux-fpga@...r.kernel.org
Subject: Re: [PATCH v3 09/18] of: overlay: validate overlay properties
 #address-cells and #size-cells

On Sun, Oct 14, 2018 at 7:26 PM <frowand.list@...il.com> wrote:
>
> From: Frank Rowand <frank.rowand@...y.com>
>
> If overlay properties #address-cells or #size-cells are already in
> the live devicetree for any given node, then the values in the
> overlay must match the values in the live tree.
>
> If the properties are already in the live tree then there is no
> need to create a changeset entry to add them since they must
> have the same value.  This reduces the memory used by the
> changeset and eliminates a possible memory leak.  This is
> verified by 12 fewer warnings during the devicetree unittest,
> as the possible memory leak warnings about #address-cells and
>
> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
> ---
>  drivers/of/overlay.c | 38 +++++++++++++++++++++++++++++++++++---
>  1 file changed, 35 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 272a0d1a5e18..ee66651db553 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -287,7 +287,12 @@ static struct property *dup_and_fixup_symbol_prop(
>   * @target may be either in the live devicetree or in a new subtree that
>   * is contained in the changeset.
>   *
> - * Some special properties are not updated (no error returned).
> + * Some special properties are not added or updated (no error returned):
> + * "name", "phandle", "linux,phandle".
> + *
> + * Properties "#address-cells" and "#size-cells" are not updated if they
> + * are already in the live tree, but if present in the live tree, the values
> + * in the overlay must match the values in the live tree.
>   *
>   * Update of property in symbols node is not allowed.
>   *
> @@ -300,6 +305,7 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
>  {
>         struct property *new_prop = NULL, *prop;
>         int ret = 0;
> +       bool check_for_non_overlay_node = false;
>
>         if (!of_prop_cmp(overlay_prop->name, "name") ||
>             !of_prop_cmp(overlay_prop->name, "phandle") ||
> @@ -322,13 +328,39 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
>         if (!new_prop)
>                 return -ENOMEM;
>
> -       if (!prop)
> +       if (!prop) {
> +
> +               check_for_non_overlay_node = true;
>                 ret = of_changeset_add_property(&ovcs->cset, target->np,
>                                                 new_prop);
> -       else
> +
> +       } else if (!of_prop_cmp(prop->name, "#address-cells")) {
> +

Hi Frank,

If we get these ERROR messages, I suggest that this function should
return an error so the overlay will be rejected.

> +               if (prop->length != 4 || new_prop->length != 4 ||
> +                   *(u32 *)prop->value != *(u32 *)new_prop->value)

                        *(u32 *)prop->value != *(u32 *)new_prop->value) {

> +                       pr_err("ERROR: overlay and/or live tree #address-cells invalid in node %pOF\n",
> +                              target->np);

                       ret = -EINVAL;
                }

Otherwise there is an ERROR message, but it continues trying to apply
the invalid overlay anyway and I get an oops.  By adding the ret =
-EINVAL, the overlay gets rejected and the oops is avoided.

> +
> +       } else if (!of_prop_cmp(prop->name, "#size-cells")) {
> +
> +               if (prop->length != 4 || new_prop->length != 4 ||
> +                   *(u32 *)prop->value != *(u32 *)new_prop->value)
> +                       pr_err("ERROR: overlay and/or live tree #size-cells invalid in node %pOF\n",
> +                              target->np);

Add the ret = -EINVAL here also.  This give me the following (if my
overlay changes #address-cells):

[   21.167551] OF: overlay: ERROR: overlay and/or live tree
#address-cells invalid in node /soc/base_fpga_region
[   21.177442] OF: overlay: add_changeset_property ret=-22
[   21.182656] create_overlay: Failed to create overlay (err=-22)

Also, I wonder if the ERROR message could be more direct.  Currently
it says the #address-cells property is invalid but that doesn't say
anything about why it's invalid.  How about something like:

 OF: overlay: ERROR: changing #address-cells not allowed (/soc/base_fpga_region)

The 'OF: overlay' part still makes it clear it's overlay related.  The
rest of it makes it clear *why* it's invalid.  This ERROR will be a
surprise for people who have been using overlays, so that could be
helpful to light the way a bit.

Alan

> +
> +       } else {
> +
> +               check_for_non_overlay_node = true;
>                 ret = of_changeset_update_property(&ovcs->cset, target->np,
>                                                    new_prop);
>
> +       }
> +
> +       if (check_for_non_overlay_node &&
> +           !of_node_check_flag(target->np, OF_OVERLAY))
> +               pr_err("WARNING: %s(), memory leak will occur if overlay removed.  Property: %pOF/%s\n",
> +                      __func__, target->np, new_prop->name);
> +
>         if (ret) {
>                 kfree(new_prop->name);
>                 kfree(new_prop->value);
> --
> Frank Rowand <frank.rowand@...y.com>
>

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