linux-hardening - Re: [PATCH v2] arm64: dts: pinephone: Add pstore support for PinePhone A64

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Date:   Fri, 25 Aug 2023 13:36:44 +0300
From:   Andrey Skvortsov <andrej.skvortzov@...il.com>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Jernej Škrabec <jernej.skrabec@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        Jarrah Gosbell <kernel@...ef.tools>,
        Arnaud Ferraris <arnaud.ferraris@...labora.com>,
        Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v2] arm64: dts: pinephone: Add pstore support for
 PinePhone A64

Hi Andre,

On 23-08-24 14:50, Andre Przywara wrote:
> On Wed, 23 Aug 2023 21:36:51 +0200
> Jernej Škrabec <jernej.skrabec@...il.com> wrote:
> 
> 
> Hi Andrey,
> 
> > send new revision as standalone e-mail, not as reply to old discussion.
> > 
> > Dne torek, 22. avgust 2023 ob 11:23:58 CEST je Andrey Skvortsov napisal(a):
> > > This patch reserves some memory in the DTS and sets up a
> > > pstore device tree node to enable pstore support.
> > > 
> > > In general any DRAM address, that isn't overwritten during a boot is
> > > suitable for pstore.
> > > 
> > > Range from 0x40000000 - 0x50000000 is heavily used by u-boot for
> > > internal use and to load kernel, fdt, fdto, scripts, pxefile and ramdisk
> > > later in the boot process. Ramdisk start address is 0x4FF00000,
> > > initramfs for kernel with some hacking features and debug info enabled
> > > can take more than 100Mb and final address will be around 0x58000000.
> > > Address 0x61000000 will most likely not overlap with that.  
> > 
> > There are other bootloaders as U-Boot, especially on PinePhone. Are you sure 
> > it works there too? What about U-Boot configuration, will those addresses still 
> > be used if configuration is changed?
> 
> Also going along with what Pavel said (that's it more a policy
> decision, not a device property), I feel like this node should be added
> by the bootloader then. And indeed U-Boot has support for that already.
> From skimming over the code in cmd/pstore.c: if you enable
> CONFIG_CMD_PSTORE and set CONFIG_CMD_PSTORE_MEM_ADDR to your chosen
> address, then the U-Boot code will insert a reserved memory node on the
> fly. Would that solve your problem?
>

I've tried pstore command in u-boot in the past to make sure it's
working there as well. I didn't know, that it adds reserved-memory
node as well. Thanks, Andre. That is very helpful.

I've tried it again without patching a kernel as you
suggested. Unfortunately it's not working on A64.

If there is no reserved-memory defined, u-boot adds a new one with
following properties:
    
    reserved-memory {
         #address-cells = <2>;
         #size-cells = <2>;
         ranges;
    }
    

But with these default address-cells and size-cells values, pstore
isn't working on A64. Root node for A64 defines 'address-cells' and 'size-cells' as 1.
    
dtc complains if reserved-memory has different address-cells and
size-cells.

```
     Warning (ranges_format): /reserved-memory:ranges: empty "ranges" property but its #address-cells (2) differs from / (1)
```

If empty reserved-memory is added to
arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi in the kernel, then
u-boot adds working pstore subnode.

```
       reserved-memory {
               #address-cells = <1>;
               #size-cells = <1>;
               ranges;

               /* bootloader will add new entries here
                * for example, for pstore.
                */
       };
```

It looks like a bug in u-boot for me. IMHO, it should look at
#address-cells/#size-cells of the root-node for default values. I have
tried that and this way pstore is working without any changes to the
kernel dts. What do you think? Should I submit fix to u-boot instead?

-- 
Best regards,
Andrey Skvortsov