[Bug 1869792] Re: [MIR] u-boot-rpi

Fri Apr 10 23:21:54 UTC 2020

This is an awkward case, I'm not sure we've got a perfect plan here.

u-boot has been in main for a while; a previous release did need to go
through -security but it appears it wasn't for security reasons:

https://launchpad.net/ubuntu/+source/u-boot/2016.01+dfsg1-2ubuntu3

The rpi family does not have any secure boot mechanism. Most of these
machines are hobbiest machines, quite often the storage is accessible
without even undoing any screws, so it's easy to say the boot process is
unlikely to be a security boundary.

So, with that in mind, I looked at only what's new, here:

$ tar tf data.tar.xz 
./
./usr/
./usr/lib/
./usr/lib/u-boot/
./usr/lib/u-boot/rpi_3/
./usr/lib/u-boot/rpi_3/u-boot.bin
./usr/lib/u-boot/rpi_3/uboot.elf
./usr/lib/u-boot/rpi_4/
./usr/lib/u-boot/rpi_4/u-boot.bin
./usr/lib/u-boot/rpi_4/uboot.elf
./usr/share/
./usr/share/doc/
./usr/share/doc/u-boot-rpi/
./usr/share/doc/u-boot-rpi/README.Debian
./usr/share/doc/u-boot-rpi/changelog.Debian.gz
./usr/share/doc/u-boot-rpi/configs/
./usr/share/doc/u-boot-rpi/configs/config.rpi_3.gz
./usr/share/doc/u-boot-rpi/configs/config.rpi_4.gz
./usr/share/doc/u-boot-rpi/copyright
./usr/share/lintian/
./usr/share/lintian/overrides/
./usr/share/lintian/overrides/u-boot-rpi
./usr/share/u-boot/
./usr/share/u-boot/rpi-config-migration

$ tar tf control.tar.xz 
./
./control
./md5sums
./postinst

The .bin and .elf files are probably safe to treat as binary blobs from
rpi and not worry about their maintenance.

The postinst and rpi-config-migration are a bit interesting. I don't
understand why they are split apart. I'd feel better if the rpi-config-
migration were run rather than sourced, just out of a sense of trying to
reduce coupling between parts that are not obviously connected.

There's no shbang line for rpi-config-migration, no set -e directly in
that file, and since it uses pipelines heavily, set -o pipefail would
probably also be useful.

Security team ACK for promoting u-boot-rpi.

If u-boot deserves a deeper look from the security team, we can arrange
that. Giving it a deeper look before 20.04 release feels infeasible, and
anyway this has been de-facto 'main' in all but process for a while
anyway, right?

Thanks

** Changed in: u-boot (Ubuntu)
       Status: New => In Progress

** Changed in: u-boot (Ubuntu)
     Assignee: Ubuntu Security Team (ubuntu-security) => (unassigned)

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https://bugs.launchpad.net/bugs/1869792

Title:
  [MIR] u-boot-rpi

Status in u-boot package in Ubuntu:
  In Progress

Bug description:
  [Availability]
  The package is already in universe.

  [Rationale]
  The package is in use in the boot sequence on all supported Raspberry Pi images, both classic and core.

  [Security]
  While there are (recent) open CVEs against u-boot, none appear relevant to the RPi port specifically. Notably:

  * CVE-2020-8432 deals with a double-free in cmd/gpt.c; GPT_CMD is not
  enabled in our rpi related u-boot configuration (because the pi does
  not support GUID partition tables).

  * CVE-2020-10648 deals with bypassing verified boot restrictions on
  FIT images; we don't use FIT u-boot images on our pi builds.

  * CVE-2019-16258 deals with attackers gaining root access by
  manipulating the u-boot console via UART; there's no expectation of
  boot security against physical access to a pi so this is irrelevant.

  * CVE-2019-14192..14204 deal with stack-based overflows against NFS
  and RPC commands. While our u-boot-rpi build does include NFS
  commands, they are not used in our boot scripts.

  All further CVEs deal with versions prior to 2019.07 (the current
  version in focal). Although it is clear vulnerabilities are reported
  with some regularity against the package, it is also evident that
  upstream responds rapidly to such reports and that many don't apply to
  our usage of the package on the pi. Furthermore, the pi is a
  relatively "open" platform with little expectation of security against
  direct physical access (after all, the storage is removable and
  unencrypted) which negates several of the reported vulnerabilities.

  [Quality assurance]
  As mentioned above, the package is already in active use in the Pi boot sequence. There are no outstanding bugs which significantly affect the usability (i.e. our images boot successfully on all supported pi models) and no important bugs open.

  There is no meaningful test suite included in the package, but then
  for a bootloader dealing with a novel platform the ultimate test is
  "does it boot?", and each update of the package is extensively
  (manually) tested against the supported models.

  The current version of the package does build-depend against python2.
  This is an issue noted in an upstream report (Debian: #943273),
  corrected in the current version in sid
  (https://salsa.debian.org/debian/u-boot/-/commit/f8a0fc63adbe13e0a3365af9b03e8315f1328913),
  and hence will be corrected next time our package is synced with
  upstream.

  [UI standards]
  The sole interactive element is the u-boot console which is only expected to be used in the circumstance that the system is un-bootable. This is (hopefully!) a sufficiently rare circumstance that the lack of localization does not pose an issue (further, it's hard to see how a bootloader could be localized given it is running prior to the OS starting and thus without knowledge of user configuration).

  [Dependencies]
  The sole runtime dependency is "awk", the installation candidates for which (gawk or mawk) are already present in main.

  [Standards compliance]
  The package installs its binaries under /usr/lib which may seem odd for something essential to booting the system but this is merely a "storage location". These binaries are then copied (via postinst currently, hopefully in future via flash-kernel) to the more appropriate /boot hierarchy.

  [Maintenance]
  The package is maintained by the Ubuntu Foundations team.

  [Background information]
  As mentioned above the package is already in active use on all our Raspberry Pi images (both classic and core). It's only recently that it was brought to my attention that the package isn't in main already. The package is essential to both the classic and core boot experiences: in the classic case for providing unpacking duties for compressed kernels, and in the core case for handling A/B boot states (neither of these facilities is currently supported by the pi's own firmware bootloader).

  This package is currently pulled into the images via the "pi-gadget"
  (https://github.com/snapcore/pi-gadget) snap which forms the basis of
  both the classic and core pi images.

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