linux-kernel - Re: [PATCH RFC 1/2] dt-bindings: mtd: ubi-volume: add 'volume-is-critical' property

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Message-ID: <3fbc4221-5967-fb9a-3cee-91cd5de2b805@huawei.com>
Date: Sun, 29 Sep 2024 19:23:12 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: Daniel Golle <daniel@...rotopia.org>
CC: Krzysztof Kozlowski <krzk@...nel.org>, Miquel Raynal
	<miquel.raynal@...tlin.com>, Richard Weinberger <richard@....at>, Vignesh
 Raghavendra <vigneshr@...com>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, John
 Crispin <john@...ozen.org>, <linux-mtd@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/2] dt-bindings: mtd: ubi-volume: add
 'volume-is-critical' property

在 2024/9/29 18:52, Daniel Golle 写道:
> On Sun, Sep 29, 2024 at 12:03:11PM +0800, Zhihao Cheng wrote:
>> 在 2024/9/28 22:38, Daniel Golle 写道:
>>> On Sat, Sep 28, 2024 at 03:45:49PM +0200, Krzysztof Kozlowski wrote:
>>>> On 28/09/2024 15:09, Daniel Golle wrote:
>>>>> On Sat, Sep 28, 2024 at 03:02:47PM +0200, Krzysztof Kozlowski wrote:
>>>>>> On 28/09/2024 14:47, Daniel Golle wrote:
>>>>>>> Add the 'volume-is-critical' boolean property which marks a UBI volume
>>>>>>> as critical for the device to boot. If set it prevents the user from
>>>>>>> all kinds of write access to the volume as well as from renaming it or
>>>>>>> detaching the UBI device it is located on.
>>>>>>>
>>>>>>> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
>>>>>>> ---
>>>>>>>    .../devicetree/bindings/mtd/partitions/ubi-volume.yaml   | 9 +++++++++
>>>>>>>    1 file changed, 9 insertions(+)
>>>>>>>
>>>>>>> diff --git a/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml b/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml
>>>>>>> index 19736b26056b..2bd751bb7f9e 100644
>>>>>>> --- a/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml
>>>>>>> +++ b/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml
>>>>>>> @@ -29,6 +29,15 @@ properties:
>>>>>>>        description:
>>>>>>>          This container may reference an NVMEM layout parser.
>>>>>>> +  volume-is-critical:
>>>>>>> +    description: This parameter, if present, indicates that the UBI volume
>>>>>>> +      contains early-boot firmware images or data which should not be clobbered.
>>>>>>> +      If set, it prevents the user from renaming the volume, writing to it or
>>>>>>> +      making any changes affecting it, as well as detaching the UBI device it is
>>>>>>> +      located on, so direct access to the underlying MTD device is prevented as
>>>>>>> +      well.
>>>>>>> +    type: boolean
>>>>>>
>>>>>> UBI volumes are mapping to partitions 1-to-1, right? So rather I would
>>>>>> propose to use partition.yaml - we already have read-only there with
>>>>>> very similar description.
>>>>>
>>>>> No, that's not the case.
>>>>>
>>>>> An MTD partition can be used as UBI device. A UBI device (and hence MTD
>>>>> partition) can host *several* UBI volumes.
>>>>>
>>>>> Marking the MTD partition as 'read-only' won't work, as UBI needs
>>>>> read-write access to perform bad block relocation, scrubbing, ...
>>>>
>>>> OK, so not partition but read-only volume.
>>>
>>> +1
>>>
>>>>
>>>>>
>>>>> Also, typically not all UBI volumes on a UBI device are
>>>>> read-only/critical but only a subset of them.
>>>>>
>>>>> But you are right that the description is inspired by the description
>>>>> of the 'read-only' property in partition.yaml ;)
>>>>>
>>>>> I initially thought to also name the property 'read-only', just like
>>>>> for MTD partitions. However, as the desired effect goes beyond
>>>>> preventing write access to the volume itself, I thought it'd be
>>>>> better to use a new name.
>>>>
>>>> Yeah, maybe... critical indeed covers multiple cases but is also
>>>> subjective. For some bootloader is critical, for other bootloader still
>>>> might be fully A/B updateable thus could be modifiable. For others, they
>>>> want to use fw_setenv from user-space so not critical at all.
>>>
>>> The case I want to cover here is the bootloader itself being stored
>>> inside a UBI volume. MediaTek's fork of ARM TrustedFirmware-A bl2 comes
>>> with support for UBI and loads BL3 (which is TF-A BL31 and U-Boot, and
>>> maybe OP-TEE as well) from a static UBI volume. Removing, renaming or
>>> altering that volume results in the device not being able to boot any
>>> more and requiring a complicated intervention (at attaching debugging
>>> UART and using low-level recovery tool) in order to recover.
>>
>> Who removes/renames the 'critical' volume? I suggest to fix it in the upper
>> layer(not in kernel). After looking through the patch 2, it seems a hack
>> solution.
> 
> The enemy is the user, the upper layer is between the keyboard and the
> screen. Just like for 'read-only' MTD partitions I'm looking
> for a similar solution for UBI which prevents the user from accidentally
> deleting or destroying the bootloader, lets say, when logged in via SSH.
> .
> 

I guess that other partitions(excepts mtd) have the similar situations, 
users could delete a rootfs(ext4) partition by operation the raw block 
device. The kernel has no way to stop user doing this, what if the user 
just want to rebuild partions?
Marking volume as critical(by a stopper in kernel) could prevent user 
mistakenly operating, but I think it is more important that user need to 
know what he/she is doing.