We must not allow other verifiers to pass things like the GRUB modules.
Instead of maintaining a blocklist, maintain an allowlist of things
that we do not care about.
This allowlist really should be made reusable, and shared by the
lockdown verifier, but this is the minimal patch addressing
security concerns where the TPM verifier was able to mark modules
as verified (or the OpenPGP verifier for that matter), when it
should not do so on shim-powered secure boot systems.
Fixes: CVE-2022-28735
Signed-off-by: Julian Andres Klode <julian.klode@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Given no core functions on i386-pc would require verifiers to work and
the only consumer of the verifier API is the pgp module, it looks good
to me that we can move the verifiers out of the kernel image and let
moddep.lst to auto-load it when pgp is loaded on i386-pc platform.
This helps to reduce the size of core image and thus can relax the
tension of exploding on some i386-pc system with very short MBR gap
size. See also a very comprehensive summary from Colin [1] about the
details.
[1] https://lists.gnu.org/archive/html/grub-devel/2021-03/msg00240.html
V2:
Drop COND_NOT_i386_pc and use !COND_i386_pc.
Add comment in kern/verifiers.c to help understanding what's going on
without digging into the commit history.
Reported-by: Colin Watson <cjwatson@debian.org>
Reviewed-by: Colin Watson <cjwatson@debian.org>
Signed-off-by: Michael Chang <mchang@suse.com>
Origin: other, https://lists.gnu.org/archive/html/grub-devel/2021-03/msg00251.html
Bug-Debian: https://bugs.debian.org/984488
Bug-Debian: https://bugs.debian.org/985374
Last-Update: 2021-09-24
Patch-Name: pc-verifiers-module.patch
Move verifiers API from a module to the kernel image, so it can be
used there as well. There are no functional changes in this patch.
Signed-off-by: Marco A Benatto <mbenatto@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Pass all commands executed by GRUB to the verifiers layer. Most verifiers will
ignore this, but some (such as the TPM verifier) want to be able to measure and
log each command executed in order to ensure that the boot state is as expected.
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
verify.h was added without include guards. This means compiling anything
including both include/grub/verify.h and include/grub/lib/cmdline.h fails
(at least grub-core/loader/arm64/linux.c.
Add the necessary include guard.
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This way if a verifier requires verification of a given file it can defer task
to another verifier (another authority) if it is not able to do it itself. E.g.
shim_lock verifier, posted as a subsequent patch, is able to verify only PE
files. This means that it is not able to verify any of GRUB2 modules which have
to be trusted on UEFI systems with secure boot enabled. So, it can defer
verification to other verifier, e.g. PGP one.
I silently assume that other verifiers are trusted and will do good job for us.
Or at least they will not do any harm.
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>
Verifiers framework provides core file verification functionality which
can be used by various security mechanisms, e.g., UEFI secure boot, TPM,
PGP signature verification, etc.
The patch contains PGP code changes and probably they should be extracted
to separate patch for the sake of clarity.
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>
