[Bug 1921387] Re: launchpad signing shimaa64.efi fails to validate

[Colin Watson]

Do we need to do anything in Launchpad other than making sure that the
relevant machines are upgraded to the latest sbsigntool?

** Project changed: launchpad => lp-signing

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to sbsigntool in Ubuntu.
https://bugs.launchpad.net/bugs/1921387

Title:
  launchpad signing shimaa64.efi fails to validate

Status in lp-signing:
  New
Status in sbsigntool package in Ubuntu:
  Fix Released
Status in sbsigntool source package in Bionic:
  Fix Committed

Bug description:
  [Impact]

   * Calculating the hash of the binary is ill defined if there are gaps
  in sections, or sections are not aligned to ensure that signature
  table is aligned.

   * This results in sbsign/sbverify to calculate incorrect hash when
  there are gaps, such as in shimaa64.efi as built on focal with sbat.

   * This was fixed in eoan, but launchpad signing service uses sbsign
  from bionic.

   * Thus if binaries have gaps launchpad is producing signatures that
  are covering the wrong authenticode hash.

  [Test Plan]

   * Signatures produced by sbsign in bionic, must be able to verify
  with sbverify from focal or later.

   * Old signatures generated by launchpad should fail validation

   * Enrolling certificate into db and booting secureboot arm VM must
  work

  ie.

  # install old sbsign

  # Test old launchpad generated signature, ensure that it fails:

  cd $(mktemp -d)
  wget http://ppa.launchpad.net/xnox/nonvirt/ubuntu/dists/hirsute/main/signed/shim-arm64/15.3-0ubuntu1~ppa1/signed.tar.gz
  tar xvf ./signed.tar.gz

  sbverify --cert 15.3-0ubuntu1~ppa1/control/uefi.crt
  15.3-0ubuntu1~ppa1/shimaa64.efi.signed

  Verification will pass with old sbsign, but it is wrong.

  # Generate new key on bionic

  update-secureboot-policy --new-key
  openssl x509 -inform der -outform pem -in /var/lib/shim-signed/mok/MOK.der -out /var/lib/shim-signed/mok/MOK.pem

  cp 15.3-0ubuntu1~ppa1/shimaa64.efi old-sbsign.efi
  cp 15.3-0ubuntu1~ppa1/shimaa64.efi new-sbsign.efi

  # self-sign the binary using the old sbsign
  sbsign --key /var/lib/shim-signed/mok/MOK.priv --cert /var/lib/shim-signed/mok/MOK.pem old-sbsign.efi

  # Detach the signature and print the message digest

  sbattach --detach old-sbsign-signature.p7c old-sbsign.efi.signed

  openssl pkcs7 -inform der -in old-sbsign-signature.p7c -print | grep
  -A5 messageDi

  # upgrade to new sbsign

  # check that verifcation now fails

  sbverify --cert 15.3-0ubuntu1~ppa1/control/uefi.crt
  15.3-0ubuntu1~ppa1/shimaa64.efi.signed

  should now fail.

  # self-sign with new sbsign
  sbsign --key /var/lib/shim-signed/mok/MOK.priv --cert /var/lib/shim-signed/mok/MOK.pem new-sbsign.efi

  # Detach the signature and print the message digest
  sbattach --detach new-sbsign-signature.p7c new-sbsign.efi.signed

  openssl pkcs7 -inform der -in new-sbsign-signature.p7c -print | grep
  -A5 messageDi

  # Also detach the launchpad signature and print digest

  sbattach --detach lp-sbsign-signature.p7c
  15.3-0ubuntu1~ppa1/shimaa64.efi.signed

  openssl pkcs7 -inform der -in lp-sbsign-signature.p7c -print | grep
  -A5 messageDi

  The correct digest is, which should be in the new-sbsign-signature.p7c:
              object: messageDigest (1.2.840.113549.1.9.4)
              set:
                OCTET STRING:
                  0000 - 6a 83 1f 9e cb 7a 68 7f-17 c0 9d 81 c0   j....zh......
                  000d - 6b 17 b2 c3 1c d7 ed b5-b3 89 49 a3 c1   k.........I..
                  001a - 8d 75 59 d3 b3 11                        .uY...

  The wrong digest is, which is in lp & old sbsign signatures:
              object: messageDigest (1.2.840.113549.1.9.4)
              set:
                OCTET STRING:
                  0000 - 2a c3 bb e6 20 27 6b b2-58 f8 8d 50 eb   *... 'k.X..P.
                  000d - 1e 88 68 a3 12 08 7a 1d-27 e5 42 e6 0e   ..h...z.'.B..
                  001a - e4 24 9a 5c 0a 92                        .$.\..

   * Additionally to that, check that existing bionic x64 binaries still
  verify correctly. I.e. grub / kernel.

  [Where problems could occur]

   * Existing edk2 OVMF machines in bionic possibly are calculating
  checksums unpadded, and thus this change will make the new signatures
  fail to validate in edk2 OVMF. However, the binaries on amd64 do not
  have gaps and thus have always had correct signatures. arm64 binaries
  with gaps do not exist in bionic.

  [Other Info]

  Original bug report:

  launchpad signed shimaa64.efi fails to validate on focal

  cd $(mktemp -d)

  wget
  http://ppa.launchpad.net/xnox/nonvirt/ubuntu/dists/hirsute/main/signed
  /shim-arm64/15.3-0ubuntu1~ppa1/signed.tar.gz

  tar xvf ./signed.tar.gz

  sbverify --cert 15.3-0ubuntu1~ppa1/control/uefi.crt
  15.3-0ubuntu1~ppa1/shimaa64.efi.signed

  Signature verification failed

  And yet inside bionic-amd64 chroot I get:

  # sbverify --cert 15.3-0ubuntu1~ppa1/control/uefi.crt 15.3-0ubuntu1~ppa1/shimaa64.efi.signed
  warning: gap in section table:
      .data   : 0x0007f000 - 0x000b3800,
      .sbat   : 0x000b4000 - 0x000b5000,
  gaps in the section table may result in different checksums
  warning: data remaining[740864 vs 800872]: gaps between PE/COFF sections?
  Signature verification OK

  However,

  If in xenial-amd64 I perform

  update-secureboot-policy new-key
  openssl x509 -inform der -outform pem -in /var/lib/shim-signed/mok/MOK.der -out /var/lib/shim-signed/mok/MOK.pem

  sbsign --key /var/lib/shim-signed/mok/MOK.priv --cert /var/lib/shim-
  signed/mok/MOK.pem 15.3-0ubuntu1~ppa1/shimaa64.efi

  sbverify --cert /var/lib/shim-signed/mok/MOK.pem 15.3-0ubuntu1~ppa1/shimaa64.efi.signed
  Signature verification OK

  Looks like something is dodgy in sbverify in bionic; i.e. it
  calculates / signs / verifies wrong hash.

To manage notifications about this bug go to:
https://bugs.launchpad.net/lp-signing/+bug/1921387/+subscriptions