[PATCH 00/16] tools: Add support for signing devicetree blobs
François Ozog
francois.ozog at linaro.org
Sat Nov 13 11:18:11 CET 2021
Hi Simon,
Le sam. 13 nov. 2021 à 04:31, Simon Glass <sjg at chromium.org> a écrit :
> Hi Heinrich,
>
> On Fri, 12 Nov 2021 at 17:02, Heinrich Schuchardt <xypron.glpk at gmx.de>
> wrote:
> >
> >
> >
> > On 11/12/21 20:49, François Ozog wrote:
> > > Hi Simon
> > >
> > > Le ven. 12 nov. 2021 à 20:36, Simon Glass <sjg at chromium.org
> > > <mailto:sjg at chromium.org>> a écrit :
> > >
> > > At present mkimage supports signing FITs, the standard U-Boot image
> > > type.
> > >
> > > Various people are opposed to using FIT since:
> > >
> > > just to be sure: I am not one of those.
> > >
> > >
> > > a) it requires adding support for FIT into other bootloaders,
> notably
> > > UEFI
> > >
> > > whatever happens to FIT is entirely orthogonal to U-Boot UEFI
> subsystem.
> > > FIT can evolve, U-Boot UEFI does not have to change.
> >
> > We already can create signed FIT images containing a UEFI binary and a
> > devcie-tree and launch the FIT image with the bootm command.
> >
> > Cf.
> > CONFIG_BOOTM_EFI
> > test/py/tests/test_efi_fit.py
> > doc/usage/bootefi.rst
> >
> > Simon, what are you missing?
>
> Some people don't want to use FIT.
>
> >
> > >
> > >
> > > b) it requires packaging a kernel in this standard U-Boot format,
> > > meaning
> > > that distros must run 'mkimage' and deal with the kernel and
> initrd
> > > being inside a FIT
> >
> > U-Boot tools are contained in distros like Debian and Ubuntu.
> > Package flash-kernel uses a script in /etc/initramfs/post-update.d/ for
> > a similar purpose. The same hook directory can be used to create a FIT
> > image with a simple bash script.
> >
> > Why do we need a new tool for signing device-trees?
> >
> > The real problem to solve is the protection of the private key used for
> > signing any file containing an initrd.
>
> Well FIT already solves that one. Either FIT is not being used, in
> which case this series is useful, or it is being used, in which case
> the initrd problem is solved.
>
> >
> > >
> > > The kernel and initrd can be dealt with in other ways. But without
> FIT,
> >
> > How can the initrd be checked without FIT?
>
> I don't know. Please check with the EFI people.
>
Ilias has made a proposal to “measure” files that do not have signatures
until files include signature.
>
> >
> > > we have no standard way of signing and grouping FDT files. Instead
> > > we must
> > > include them in the distro as separate files.
> > >
> > > In particular, some sort of mechanism for verifying FDT files is
> needed.
> > > One option would be to tack a signature on before or after the
> file,
> > > processing it accordingly. But due to the nature of the FDT binary
> > > format,
> > > it is possible to embed a signature inside the FDT itself, which
> is very
> > > convenient.
> > >
> > > This series provides a tool, fdt_sign, which can add a signature
> to an
> > > FDT. The signature can be checked later, preventing any change to
> > > the FDT,
> > > other than in permitted nodes (e.g. /chosen).
> >
Shouldn’t devicetree.org and kernel.org folks involved in this DT signing
effort ? I believe there are parrallel efforts in this area. Or is it a
private <u-boot FDT sign>? in that case, they do not need to be involved.
Depending on the case, you may want to split the patch series in a number
of chunks.
>
> > I am not aware of any standard defining which nodes may be changed in
> > the FDT fixup and which may not be changed.
> >
> > How can we discover which nodes were excluded from the signature after
> > the signature?
>
> There is no way at present. I decided against adding a list of signed
> nodes. We can of course add whatever is useful here.
>
> >
> > >
> > > This series also provides a fdt_check_sign tool, used to check
> > > signatures.
> > >
> > > Both of these tools are stand-alone do not require mkimage or FIT.
> > >
> > > As with FIT signing, multiple signatures are possible, but in this
> case
> > > that requires that fit_sign be called once for each signature. To
> > > make the
> > > check fail if a signature does not match, it should be marked as
> > > 'required' using the -r flag to fdt_sign.
> > >
> > > Run-time support for checking FDT signatures could be added to
> U-Boot
> > > fairly easily, but needs further discussion as the correct plumbing
> > > needs
> > > to be determined.
> > >
> > > For now there is absolutely no configurability in the signature
> > > mechanism.
> >
> > I would have expected a description of what a signature looks like. I
> > don't wont to reverse engineer your patches.
> >
> > Please, describe this in doc/develop/ and in this cover-letter.
>
> It is the same format as the FIT signature, an RSA signature. See here:
>
>
> https://github.com/u-boot/u-boot/blob/master/doc/uImage.FIT/signature.txt#L162
>
> >
> > This series should have been sent as RFC.
>
> The last time I did that it disappeared without trace. You can of
> course make comments on any series I send.
>
> Regards,
> Simon
>
> >
> > Best regards
> >
> > Heinrich
> >
> > > It would of course be possible to adjust which nodes are signed,
> as is
> > > done for FIT, but that needs further discussion also. The omission
> > > of the
> > > /chosen node is implemented in h_exclude_nodes() like this:
> > >
> > > if (type == FDT_IS_NODE) {
> > > /* Ignore the chosen node as well as /signature and
> subnodes */
> > > if (!strcmp("/chosen", data) || !strncmp("/signature",
> data, 10))
> > > return 0;
> > > }
> > >
> > > Man pages are provided with example usage of the tools. Use this
> to view
> > > them:
> > >
> > > man -l doc/fdt_check_sign.1
> > >
> > > This series also includes various clean-ups noticed along the way,
> > > as well
> > > as refactoring to avoid code duplication with the new tools. The
> > > last four
> > > patches are the new code.
> > >
> > > This series is available at u-boot-dm/fdt-sign-working :
> > >
> > >
> https://source.denx.de/u-boot/custodians/u-boot-dm/-/tree/fdt-sign-working
> > > <
> https://source.denx.de/u-boot/custodians/u-boot-dm/-/tree/fdt-sign-working
> >
> > >
> > >
> > > Simon Glass (16):
> > > rsa: Add debugging for failure cases
> > > fit_check_sign: Update help to mention the key is in a dtb
> > > tools: Move copyfile() into a common file
> > > tools: Avoid leaving extra data at the end of copied files
> > > tools: Improve comments in signing functions
> > > tools: Drop unused name in image-host
> > > tools: Avoid confusion between keys and signatures
> > > tools: Tidy up argument order in fit_config_check_sig()
> > > tools: Pass the key blob around
> > > image: Return destination node for add_verify_data() method
> > > tools: Pass public-key node through to caller
> > > tools: mkimage: Show where signatures/keys are written
> > > tools: Add a new tool to sign FDT blobs
> > > tools: Add a new tool to check FDT-blob signatures
> > > test: Add a test for FDT signing
> > > tools: Add man pages for fdt_sign and fdt_check_sign
> > >
> > > MAINTAINERS | 7 +
> > > boot/image-fit-sig.c | 151 +++++++++----
> > > boot/image-fit.c | 12 +-
> > > common/spl/spl_fit.c | 3 +-
> > > doc/fdt_check_sign.1 | 74 +++++++
> > > doc/fdt_sign.1 | 111 ++++++++++
> > > include/image.h | 80 ++++++-
> > > include/u-boot/ecdsa.h | 5 +-
> > > include/u-boot/rsa.h | 5 +-
> > > lib/ecdsa/ecdsa-libcrypto.c | 4 +-
> > > lib/rsa/rsa-sign.c | 5 +-
> > > lib/rsa/rsa-verify.c | 13 +-
> > > test/py/tests/test_fdt_sign.py | 83 ++++++++
> > > test/py/tests/test_vboot.py | 21 +-
> > > test/py/tests/vboot/sign-fdt.dts | 23 ++
> > > test/py/tests/vboot_comm.py | 22 ++
> > > tools/Makefile | 10 +-
> > > tools/fdt-host.c | 353
> +++++++++++++++++++++++++++++++
> > > tools/fdt_check_sign.c | 85 ++++++++
> > > tools/fdt_host.h | 46 ++++
> > > tools/fdt_sign.c | 210 ++++++++++++++++++
> > > tools/fit_check_sign.c | 4 +-
> > > tools/fit_common.c | 69 ++++++
> > > tools/fit_common.h | 23 ++
> > > tools/fit_image.c | 59 +-----
> > > tools/image-fdt-sig.c | 254 ++++++++++++++++++++++
> > > tools/image-host.c | 155 +++++++++++---
> > > tools/imagetool.h | 4 +
> > > tools/mkimage.c | 4 +
> > > 29 files changed, 1714 insertions(+), 181 deletions(-)
> > > create mode 100644 doc/fdt_check_sign.1
> > > create mode 100644 doc/fdt_sign.1
> > > create mode 100644 test/py/tests/test_fdt_sign.py
> > > create mode 100644 test/py/tests/vboot/sign-fdt.dts
> > > create mode 100644 test/py/tests/vboot_comm.py
> > > create mode 100644 tools/fdt-host.c
> > > create mode 100644 tools/fdt_check_sign.c
> > > create mode 100644 tools/fdt_sign.c
> > > create mode 100644 tools/image-fdt-sig.c
> > >
> > > --
> > > 2.34.0.rc1.387.gb447b232ab-goog
> > >
> > > --
> > >
> > > François-Frédéric Ozog | /Director Business Development/
> > > T: +33.67221.6485
> > > francois.ozog at linaro.org <mailto:francois.ozog at linaro.org> | Skype:
> ffozog
> > >
> > >
>
--
François-Frédéric Ozog | *Director Business Development*
T: +33.67221.6485
francois.ozog at linaro.org | Skype: ffozog
More information about the U-Boot
mailing list