Mike,

2017-04-18 19:37 GMT+02:00 Kees Cook [off-list ref]:

On Tue, Apr 18, 2017 at 9:42 AM, Enric Balletbo i Serra
[off-list ref] wrote:

quoted

Hello,

Some of these patches were send few years back, I saw that first
version was send to this list in 2010, and after version 4 did not
land [1]. Some days ago I resend the patches [2] and few hours later I
noticed that one year ago was send a v5 version [3] and I was not aware.

There was some discussion about v5 and during the discussion Mike Snitzer
proposed that at least a change of the syntax is required, we're really
interested on see this upstream as is extensively used in ChromeOS based
devices so I'm wondering if we can restart the discussion and hopefully
we will be able to do the modifications needed.

So my first question is, apart of the change of the syntax, what more
should be changed?

AFAIK, this was the main change needed. Change the syntax and plumb
into the ioctl interface. The discussion ended with Mike being open to
the idea, and for me to go work on it. I haven't had time to work on
it, though, so it has continued to be a locally carried patch:
https://www.redhat.com/archives/dm-devel/2016-February/msg00199.html

From your email:

quoted

quoted

quoted

2) If you are able to adequately justify the need for dm=:
I'd much rather the dm= kernel commandline be a simple series of
comma-delimited dmsetup-like commands.

You'd handle each command with extremely basic parsing:
 <dm_ioctl_cmd> <args> [, <dm_ioctl_cmd> <args>]
(inventing a special token to denote <newline>, to support tables with
multiple entries, rather than relying on commas and counts, etc)

I'm wondering if a command line like this would be acceptable.

Format is:
  dm="<dev_name> <uuid> <mode>,  <table>[, <table>][; <dev_name>
<uuid> <mode>,  <table>[, <table>]][; ... ]"

where:
  <dev_name> ::=  The device name
  <uuid>          ::=  xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx | "none"
  <mode>        ::= "ro" | "rw"
  <table>         ::= <start sector> <end sector> <target name>
<target parmaters>

An example of booting to a linear array:

 dm="lroot none rw, 0 2097152 linear /dev/sda2 0, 2097152 2097152
linear /dev/sda3 0, 4194304 2097152 linear /dev/sda4 0"

Equivalent dmsetup command:

echo -e "0 2097152 linear /dev/sda2 0"\\n"2097152 2097152 linear
/dev/sda3 0"\\n"4194304 2097152 linear /dev/sda4 0" | sudo dmsetup
create lroot

An example of multiple device-mappers, with the dm="..." contents shown
here split on multiple lines for readability:

    vroot none ro,
      0 2097152 verity 1 /dev/sdb2 /dev/sdb3 4096 4096 262144 1 sha256 \
      289b52edac1ac4f4c32c8f765795615a85d4daa454677d21a6d8767c4627dc48 \
      632d7fe427a23a8e88493c553298a779997478a143d86da5d56a65db8a1f2a38;
    vram none rw,
      0 32768 linear 1:0 0,
      32768 32768 linear 1:1 0

Thanks,
 Enric

More recently David Zeuthen has been poking at this code, so I've
included him on CC here, in case there are new developments.

-Kees

quoted

Thanks for your help,
 Enric

[1] Patchwork links:
    https://patchwork.kernel.org/patch/104857/
    https://patchwork.kernel.org/patch/104856/
    https://patchwork.kernel.org/patch/104858/

[2] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1375276.html

[3] https://www.redhat.com/archives/dm-devel/2016-February/msg00112.html


Brian Norris (1):
  dm: make some mapped_device functions available

Will Drewry (2):
  dm: export a table+mapped device to the ioctl interface
  init: add support to directly boot to a mapped device

 Documentation/admin-guide/kernel-parameters.rst |   1 +
 Documentation/admin-guide/kernel-parameters.txt |   3 +
 Documentation/device-mapper/boot.txt            |  65 ++++
 drivers/md/dm-ioctl.c                           |  36 ++
 drivers/md/dm.h                                 |   8 -
 include/linux/device-mapper.h                   |  19 +
 init/Makefile                                   |   1 +
 init/do_mounts.c                                |   1 +
 init/do_mounts.h                                |  10 +
 init/do_mounts_dm.c                             | 448 ++++++++++++++++++++++++
 10 files changed, 584 insertions(+), 8 deletions(-)
 create mode 100644 Documentation/device-mapper/boot.txt
 create mode 100644 init/do_mounts_dm.c

--
2.9.3

--
Kees Cook
Pixel Security

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