Kernel 4.14: Using dm-verity with squashfs rootfs - mounting issue

[Pintu Agarwal]

Dear Thomas, Mikulas,
Need your help in root causing my dm-verity issue with squashfs.
Please see my comments inline.

On Tue, 31 Aug 2021 at 18:49, Pintu Agarwal <pintu.ping at gmail.com> wrote:

> > No, but you can backport it easily. Back at
> > http://lists.infradead.org/pipermail/openwrt-devel/2019-November/025967.html
> > I provided backports of this feature to OpenWrt, for the 4.14 and 4.19
> > kernels.
> >
> Yes, I can backport it to our 4.14 Kernel.
> Can you share the list of patches to be backported to make it work on 4.14 ?
> If it's backported also I need to report to our internal kernel, but
> it might be slightly easier.
> Please share the details.
>

I am interested to backport dm-mod.create related patches to our 4.14 kernel.
Please let me know where can I find all the patches ?
Is it already part of mainline 4.14 ?
Please share the list of commits (from mainline) that we need to pull
and backport.

> > > Here is our kernel command line:
> > >
> > > [    0.000000] Kernel command line: ro rootwait
> > > console=ttyMSM0,115200,n8 ....  verity="95384 11923
> > > 16da5e4bbc706e5d90511d2a3dae373b5d878f9aebd522cd614a4faaace6baa3 12026
> > > " rootfstype=squashfs ubi.mtd=40,0,30 ubi.block=0,0 root=/dev/dm-0
> > > .... init=/sbin/init root=/dev/dm-0 dm="rootfs none ro,0 95384 verity
> > > 1 /dev/ubiblock0_0 /dev/mtdblock53 4096 4096 11923 8 sha256
> > > 16da5e4bbc706e5d90511d2a3dae373b5d878f9aebd522cd614a4faaace6baa3
> > > aee087a5be3b982978c923f566a94613496b417f2af592639bc80d141e34dfe7 10
> > > restart_on_corruption ignore_zero_blocks use_fec_from_device
> > > /dev/mtdblock53 fec_roots 2 fec_blocks 12026 fec_start 12026" ...
> >
> > I don't see how this can work without the dm-mod.create feature. Are
> > you sure the verity= and dm= kernel arguments exist?
>
I checked a little further and yes there is "dm=" command line in
kernel available.
This is already working with ext4 glue, but was never tried with squashfs.
I think it is mainline derived from Android.
https://patchwork.kernel.org/project/dm-devel/patch/2c01b2a43a46fab760208d7af3a7af37eec8c41a.1537936397.git.helen.koike@collabora.com/
https://github.com/projectceladon/device-androidia-kernel/blob/master/init/do_mounts_dm.c

Mostly, this is the main repo where our source might be derived:
https://github.com/android-linux-stable/msm-4.14

Can we backport the patches here ?
If I get the list I can try it.

>
> Also, you mentioned:
> >>> Here, it definitely worked to append the hash tree to the squashfs
> >>> image and store them in the same partition.
> Can you share some details about it ?
> How it can be done since squashfs is readonly.
Can you share your reference, how are you appending the hash tree ?
Let me try the same.

But it seems like the underlying concept is the same for both
"dm-mod.create" and "dm=".
However, I am not sure if there are any changes required for squashfs
as block device..

Errors:
Currently, we are getting this in boot logs:

[    4.962188] device-mapper: init: attempting early device configuration.
[    4.969699] device-mapper: init: created device '253:0'
[    4.975503] device-mapper: init: adding target '0 95384 verity 1
/dev/ubiblock0_0 /dev/mtdblock53 4096 4096 11923 8 sha256
8fc2e4bb751f4b3145a486a0f4f1b58149ba3eedc2a67312f31fbee131380dab
aee087a5be3b982978c923f566a94613496b417f2af592639bc80d141e34dfe7 10
restart_on_corruption ignore_zero_blocks use_fec_from_device
/dev/mtdblock53 fec_roots 2 fec_blocks 12026 fec_start 12026'
[    4.992323] device-mapper: verity: sha256 using implementation
"sha256-generic"
[    5.015568] device-mapper: init: dm-0 is ready
[   10.080065] prepare_namespace: dm_run_setup - done
[   10.080093] prepare_namespace: saved_root_name: /dev/dm-0
[   10.083903] prepare_namespace: Inside: name_to_dev_t
[   10.089605] prepare_namespace: Calling - mount_root() ...
[   10.094519] [PINTU]: mount_block_root: called with input name:
/dev/root, fs_names: squashfs
[   10.263510] [PINTU]: do_mount_root: sys_mount failed: err: -22
[   10.263544] [PINTU]: mount_block_root: do_mount_root: err: -22, p:
squashfs, flags: 32769, root_mount_data: (null)
[..]
[   10.745672] No filesystem could mount root, tried:
[   10.745676]  squashfs
[   10.748015]
[   10.755232] Kernel panic - not syncing: VFS: Unable to mount root
fs on unknown-block(253,0)

It seems the rootfs could not mount due to invalid arguments.
Not sure which arguments are invalid here...


Thanks,
Pintu