linux-hardening - Re: [PATCH v4 1/2] dt-bindings: ramoops: Inherit reserve memory property

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Date:   Fri, 27 Jan 2023 14:05:44 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
Cc:     linux-hardening@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH v4 1/2] dt-bindings: ramoops: Inherit reserve memory property

On Fri, Jan 27, 2023 at 10:01 AM Mukesh Ojha <quic_mojha@...cinc.com> wrote:
>
> The reserved memory region for ramoops is assumed to be at a
> fixed and known location when read from the devicetree. This
> is not desirable in an environment where it is preferred the
> region to be dynamically allocated at runtime, as opposed to
> being fixed at compile time.

I don't see how this can work. How do you find the region after
rebooting? Or this is only used for the current boot? If so, provide a
userspace interface to configure it (or the existing module params).

The addition of 'size' type regions was primarily for large carveouts
that needed to be allocated before anything else. ramoops is not that.
It's 10s or 100s of KB at most.


> So, update the ramoops binding by inheriting some reserve memory
> property to allocate the ramoops region dynamically.
>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Guilherme G. Piccoli <gpiccoli@...lia.com>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
> Signed-off-by: Mukesh Ojha <quic_mojha@...cinc.com>
> ---
> Changes in v4:
>  - Addressed comment made by Krzysztof on ramoops node name.
>
> Changes in v3:
>  - Fixed yaml error and updated commit text as per comment.
>
> Change in v2:
>   - Added this patch as per changes going to be done in patch 3/3
>
>  .../bindings/reserved-memory/ramoops.yaml          | 34 ++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/reserved-memory/ramoops.yaml b/Documentation/devicetree/bindings/reserved-memory/ramoops.yaml
> index 0391871..8741626 100644
> --- a/Documentation/devicetree/bindings/reserved-memory/ramoops.yaml
> +++ b/Documentation/devicetree/bindings/reserved-memory/ramoops.yaml
> @@ -10,7 +10,8 @@ description: |
>    ramoops provides persistent RAM storage for oops and panics, so they can be
>    recovered after a reboot. This is a child-node of "/reserved-memory", and
>    is named "ramoops" after the backend, rather than "pstore" which is the
> -  subsystem.
> +  subsystem. This region can be reserved both statically or dynamically by
> +  using appropriate property in device tree.
>
>    Parts of this storage may be set aside for other persistent log buffers, such
>    as kernel log messages, or for optional ECC error-correction data.  The total
> @@ -112,7 +113,13 @@ unevaluatedProperties: false
>
>  required:
>    - compatible
> -  - reg
> +
> +oneOf:
> +  - required:
> +      - reg
> +
> +  - required:
> +      - size
>
>  anyOf:
>    - required: [record-size]
> @@ -142,3 +149,26 @@ examples:
>              };
>          };
>      };
> +
> +  - |
> +    / {

You can't have multiple root node examples. Check the example dts, the
examples will be merged together.

> +        compatible = "foo";
> +        model = "foo";
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +
> +        reserved-memory {
> +            #address-cells = <1>;
> +            #size-cells = <1>;
> +            ranges;
> +
> +            ramoops_region: ramoops {
> +                compatible = "ramoops";
> +                alloc-ranges = <0x00000000 0xffffffff>;
> +                size = <0x0 0x10000>;       /* 64kB */
> +                console-size = <0x8000>;    /* 32kB */
> +                record-size = <0x400>;      /*  1kB */
> +                ecc-size = <16>;
> +            };
> +        };
> +    };
> --
> 2.7.4
>