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

Thu Mar 25 14:23:16 UTC 2021

** Description changed:

  [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.

-  * Signatures produced by sbsign in bionic, must be able to verify with
- pesigcheck
+  * Old signatures generated by launchpad should fail validation

-  * Existing signatures generated by launchpad should fail validation
+  * Enrolling certificate into db and booting secureboot arm VM must work

  ie.

  # 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
  ...
  Signature verification failed

  Is the correct output

- # Test that pesigcheck fails too
- 
- openssl x509 -outform der -out 15.3-0ubuntu1~ppa1/control/uefi.der -in
- 15.3-0ubuntu1~ppa1/control/uefi.crt
- 
- pesigcheck -i 15.3-0ubuntu1~ppa1/shimaa64.efi.signed -c 15.3-0ubuntu1~ppa1/control/uefi.der
- pesigcheck: "15.3-0ubuntu1~ppa1/shimaa64.efi.signed" is invalid.
- 
  # Generate new key on bionic, resign using new sbsigntool, and check
  that it is now all good:

  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

- pesigcheck -i 15.3-0ubuntu1~ppa1/shimaa64.efi.signed -c /var/lib/shim-
- signed/mok/MOK.der
+ Copy the signed binary & cert to focal, and check that sbverify verifies
+ them.
+ 

  [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.

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https://bugs.launchpad.net/bugs/1921387

Title:
  launchpad signing shimaa64.efi fails to validate

Status in Launchpad itself:
  New
Status in sbsigntool package in Ubuntu:
  Fix Released
Status in sbsigntool source package in Bionic:
  New

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.

  # 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
  ...
  Signature verification failed

  Is the correct output

  # Generate new key on bionic, resign using new sbsigntool, and check
  that it is now all good:

  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

  Copy the signed binary & cert to focal, and check that sbverify
  verifies them.

  [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.

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