QSB-100: Incorrect handling of PCI devices with phantom functions (XSA-449)

We have published Qubes Security Bulletin 100: Incorrect handling of PCI devices with phantom functions (XSA-449). The text of this QSB and its accompanying cryptographic signatures are reproduced below. For an explanation of this announcement and instructions for authenticating this QSB, please see the end of this announcement.

Qubes Security Bulletin 100


             ---===[ Qubes Security Bulletin 100 ]===---

                              2024-01-30

   Incorrect handling of PCI devices with phantom functions (XSA-449)

Changelog
----------

2024-01-30: Original QSB published
2024-02-06: Revise language

User action
------------

Continue to update normally [1] in order to receive the security updates
described in the "Patching" section below. No other user action is
required in response to this QSB.

Summary
--------

On 2024-01-30, the Xen Project published XSA-449, "pci: phantom
functions assigned to incorrect contexts" [3]:

| PCI devices can make use of a functionality called phantom functions,
| that when enabled allows the device to generate requests using the IDs
| of functions that are otherwise unpopulated.  This allows a device to
| extend the number of outstanding requests.
|
| Such phantom functions need an IOMMU context setup, but failure to
| setup the context is not fatal when the device is assigned.  Not
| failing device assignment when such failure happens can lead to the
| primary device being assigned to a guest, while some of the phantom
| functions are assigned to a different domain.

Impact
-------

The impact as described by the Xen Project:

| Under certain circumstances a malicious guest assigned a PCI device
| with phantom functions may be able to access memory from a previous
| owner of the device.

In Qubes OS, this means that a PCI device assigned to some qube (like
sys-net or sys-usb) can retain access to dom0 memory. When this happens,
the qube to which the device is assigned can compromise the whole
system. However, a malicious qube cannot itself cause this condition, as
it occurs before the malicious qube starts running. For such an attack
to be feasible, it would have to be combined with some other method for
causing PCI device assignment to fail.

Affected systems
-----------------

Every Qubes OS system that has at least one passthrough PCI device with
phantom functions is affected.

Patching
---------

The following packages contain security updates that address the
vulnerabilities described in this bulletin:

  For Qubes 4.1, in dom0:
  - Xen packages, version 4.14.6-6

  For Qubes 4.2, in dom0:
  - Xen packages, version 4.17.3-2

These packages will migrate from the security-testing repository to the
current (stable) repository over the next two weeks after being tested
by the community. [2] Once available, the packages are to be installed
via the Qubes Update tool or its command-line equivalents. [1]

Dom0 must be restarted afterward in order for the updates to take
effect.

If you use Anti Evil Maid, you will need to reseal your secret
passphrase to new PCR values, as PCR18+19 will change due to the new
Xen binaries.

Credits
--------

See the original Xen Security Advisory.

References
-----------

[1] https://www.qubes-os.org/doc/how-to-update/
[2] https://www.qubes-os.org/doc/testing/
[3] https://xenbits.xen.org/xsa/advisory-449.html

--
The Qubes Security Team
https://www.qubes-os.org/security/

Source: https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-100-2024.txt

Marek Marczykowski-Górecki’s PGP signature

-----BEGIN PGP SIGNATURE-----
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=fOAF
-----END PGP SIGNATURE-----

Source: https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-100-2024.txt.sig.marmarek

Simon Gaiser (aka HW42)’s PGP signature

-----BEGIN PGP SIGNATURE-----
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=Kk0O
-----END PGP SIGNATURE-----

Source: https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-100-2024.txt.sig.simon

What is the purpose of this announcement?

The purpose of this announcement is to inform the Qubes community that a new Qubes security bulletin (QSB) has been published.

What is a Qubes security bulletin (QSB)?

A Qubes security bulletin (QSB) is a security announcement issued by the Qubes security team. A QSB typically provides a summary and impact analysis of one or more recently-discovered software vulnerabilities, including details about patching to address them. For a list of all QSBs, see Qubes security bulletins (QSBs).

Why should I care about QSBs?

QSBs tell you what actions you must take in order to protect yourself from recently-discovered security vulnerabilities. In most cases, security vulnerabilities are addressed by updating normally. However, in some cases, special user action is required. In all cases, the required actions are detailed in QSBs.

What are the PGP signatures that accompany QSBs?

A PGP signature is a cryptographic digital signature made in accordance with the OpenPGP standard. PGP signatures can be cryptographically verified with programs like GNU Privacy Guard (GPG). The Qubes security team cryptographically signs all QSBs so that Qubes users have a reliable way to check whether QSBs are genuine. The only way to be certain that a QSB is authentic is by verifying its PGP signatures.

Why should I care whether a QSB is authentic?

A forged QSB could deceive you into taking actions that adversely affect the security of your Qubes OS system, such as installing malware or making configuration changes that render your system vulnerable to attack. Falsified QSBs could sow fear, uncertainty, and doubt about the security of Qubes OS or the status of the Qubes OS Project.

How do I verify the PGP signatures on a QSB?

The following command-line instructions assume a Linux system with git and gpg installed. (For Windows and Mac options, see OpenPGP software.)

  1. Obtain the Qubes Master Signing Key (QMSK), e.g.:

    $ gpg --fetch-keys https://keys.qubes-os.org/keys/qubes-master-signing-key.asc
    gpg: directory '/home/user/.gnupg' created
    gpg: keybox '/home/user/.gnupg/pubring.kbx' created
    gpg: requesting key from 'https://keys.qubes-os.org/keys/qubes-master-signing-key.asc'
    gpg: /home/user/.gnupg/trustdb.gpg: trustdb created
    gpg: key DDFA1A3E36879494: public key "Qubes Master Signing Key" imported
    gpg: Total number processed: 1
    gpg:               imported: 1
    

    (For more ways to obtain the QMSK, see How to import and authenticate the Qubes Master Signing Key.)

  2. View the fingerprint of the PGP key you just imported. (Note: gpg> indicates a prompt inside of the GnuPG program. Type what appears after it when prompted.)

    $ gpg --edit-key 0x427F11FD0FAA4B080123F01CDDFA1A3E36879494
    gpg (GnuPG) 2.2.27; Copyright (C) 2021 Free Software Foundation, Inc.
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.
       
       
    pub  rsa4096/DDFA1A3E36879494
         created: 2010-04-01  expires: never       usage: SC
         trust: unknown       validity: unknown
    [ unknown] (1). Qubes Master Signing Key
       
    gpg> fpr
    pub   rsa4096/DDFA1A3E36879494 2010-04-01 Qubes Master Signing Key
     Primary key fingerprint: 427F 11FD 0FAA 4B08 0123  F01C DDFA 1A3E 3687 9494
    
  3. Important: At this point, you still don’t know whether the key you just imported is the genuine QMSK or a forgery. In order for this entire procedure to provide meaningful security benefits, you must authenticate the QMSK out-of-band. Do not skip this step! The standard method is to obtain the QMSK fingerprint from multiple independent sources in several different ways and check to see whether they match the key you just imported. For more information, see How to import and authenticate the Qubes Master Signing Key.

    Tip: After you have authenticated the QMSK out-of-band to your satisfaction, record the QMSK fingerprint in a safe place (or several) so that you don’t have to repeat this step in the future.

  4. Once you are satisfied that you have the genuine QMSK, set its trust level to 5 (“ultimate”), then quit GnuPG with q.

    gpg> trust
    pub  rsa4096/DDFA1A3E36879494
         created: 2010-04-01  expires: never       usage: SC
         trust: unknown       validity: unknown
    [ unknown] (1). Qubes Master Signing Key
       
    Please decide how far you trust this user to correctly verify other users' keys
    (by looking at passports, checking fingerprints from different sources, etc.)
       
      1 = I don't know or won't say
      2 = I do NOT trust
      3 = I trust marginally
      4 = I trust fully
      5 = I trust ultimately
      m = back to the main menu
       
    Your decision? 5
    Do you really want to set this key to ultimate trust? (y/N) y
       
    pub  rsa4096/DDFA1A3E36879494
         created: 2010-04-01  expires: never       usage: SC
         trust: ultimate      validity: unknown
    [ unknown] (1). Qubes Master Signing Key
    Please note that the shown key validity is not necessarily correct
    unless you restart the program.
       
    gpg> q
    
  5. Use Git to clone the qubes-secpack repo.

    $ git clone https://github.com/QubesOS/qubes-secpack.git
    Cloning into 'qubes-secpack'...
    remote: Enumerating objects: 4065, done.
    remote: Counting objects: 100% (1474/1474), done.
    remote: Compressing objects: 100% (742/742), done.
    remote: Total 4065 (delta 743), reused 1413 (delta 731), pack-reused 2591
    Receiving objects: 100% (4065/4065), 1.64 MiB | 2.53 MiB/s, done.
    Resolving deltas: 100% (1910/1910), done.
    
  6. Import the included PGP keys. (See our PGP key policies for important information about these keys.)

    $ gpg --import qubes-secpack/keys/*/*
    gpg: key 063938BA42CFA724: public key "Marek Marczykowski-Górecki (Qubes OS signing key)" imported
    gpg: qubes-secpack/keys/core-devs/retired: read error: Is a directory
    gpg: no valid OpenPGP data found.
    gpg: key 8C05216CE09C093C: 1 signature not checked due to a missing key
    gpg: key 8C05216CE09C093C: public key "HW42 (Qubes Signing Key)" imported
    gpg: key DA0434BC706E1FCF: public key "Simon Gaiser (Qubes OS signing key)" imported
    gpg: key 8CE137352A019A17: 2 signatures not checked due to missing keys
    gpg: key 8CE137352A019A17: public key "Andrew David Wong (Qubes Documentation Signing Key)" imported
    gpg: key AAA743B42FBC07A9: public key "Brennan Novak (Qubes Website & Documentation Signing)" imported
    gpg: key B6A0BB95CA74A5C3: public key "Joanna Rutkowska (Qubes Documentation Signing Key)" imported
    gpg: key F32894BE9684938A: public key "Marek Marczykowski-Górecki (Qubes Documentation Signing Key)" imported
    gpg: key 6E7A27B909DAFB92: public key "Hakisho Nukama (Qubes Documentation Signing Key)" imported
    gpg: key 485C7504F27D0A72: 1 signature not checked due to a missing key
    gpg: key 485C7504F27D0A72: public key "Sven Semmler (Qubes Documentation Signing Key)" imported
    gpg: key BB52274595B71262: public key "unman (Qubes Documentation Signing Key)" imported
    gpg: key DC2F3678D272F2A8: 1 signature not checked due to a missing key
    gpg: key DC2F3678D272F2A8: public key "Wojtek Porczyk (Qubes OS documentation signing key)" imported
    gpg: key FD64F4F9E9720C4D: 1 signature not checked due to a missing key
    gpg: key FD64F4F9E9720C4D: public key "Zrubi (Qubes Documentation Signing Key)" imported
    gpg: key DDFA1A3E36879494: "Qubes Master Signing Key" not changed
    gpg: key 1848792F9E2795E9: public key "Qubes OS Release 4 Signing Key" imported
    gpg: qubes-secpack/keys/release-keys/retired: read error: Is a directory
    gpg: no valid OpenPGP data found.
    gpg: key D655A4F21830E06A: public key "Marek Marczykowski-Górecki (Qubes security pack)" imported
    gpg: key ACC2602F3F48CB21: public key "Qubes OS Security Team" imported
    gpg: qubes-secpack/keys/security-team/retired: read error: Is a directory
    gpg: no valid OpenPGP data found.
    gpg: key 4AC18DE1112E1490: public key "Simon Gaiser (Qubes Security Pack signing key)" imported
    gpg: Total number processed: 17
    gpg:               imported: 16
    gpg:              unchanged: 1
    gpg: marginals needed: 3  completes needed: 1  trust model: pgp
    gpg: depth: 0  valid:   1  signed:   6  trust: 0-, 0q, 0n, 0m, 0f, 1u
    gpg: depth: 1  valid:   6  signed:   0  trust: 6-, 0q, 0n, 0m, 0f, 0u
    
  7. Verify signed Git tags.

    $ cd qubes-secpack/
    $ git tag -v `git describe`
    object 266e14a6fae57c9a91362c9ac784d3a891f4d351
    type commit
    tag marmarek_sec_266e14a6
    tagger Marek Marczykowski-Górecki 1677757924 +0100
       
    Tag for commit 266e14a6fae57c9a91362c9ac784d3a891f4d351
    gpg: Signature made Thu 02 Mar 2023 03:52:04 AM PST
    gpg:                using RSA key 2D1771FE4D767EDC76B089FAD655A4F21830E06A
    gpg: Good signature from "Marek Marczykowski-Górecki (Qubes security pack)" [full]
    

    The exact output will differ, but the final line should always start with gpg: Good signature from... followed by an appropriate key. The [full] indicates full trust, which this key inherits in virtue of being validly signed by the QMSK.

  8. Verify PGP signatures, e.g.:

    $ cd QSBs/
    $ gpg --verify qsb-087-2022.txt.sig.marmarek qsb-087-2022.txt
    gpg: Signature made Wed 23 Nov 2022 04:05:51 AM PST
    gpg:                using RSA key 2D1771FE4D767EDC76B089FAD655A4F21830E06A
    gpg: Good signature from "Marek Marczykowski-Górecki (Qubes security pack)" [full]
    $ gpg --verify qsb-087-2022.txt.sig.simon qsb-087-2022.txt
    gpg: Signature made Wed 23 Nov 2022 03:50:42 AM PST
    gpg:                using RSA key EA18E7F040C41DDAEFE9AA0F4AC18DE1112E1490
    gpg: Good signature from "Simon Gaiser (Qubes Security Pack signing key)" [full]
    $ cd ../canaries/
    $ gpg --verify canary-034-2023.txt.sig.marmarek canary-034-2023.txt
    gpg: Signature made Thu 02 Mar 2023 03:51:48 AM PST
    gpg:                using RSA key 2D1771FE4D767EDC76B089FAD655A4F21830E06A
    gpg: Good signature from "Marek Marczykowski-Górecki (Qubes security pack)" [full]
    $ gpg --verify canary-034-2023.txt.sig.simon canary-034-2023.txt
    gpg: Signature made Thu 02 Mar 2023 01:47:52 AM PST
    gpg:                using RSA key EA18E7F040C41DDAEFE9AA0F4AC18DE1112E1490
    gpg: Good signature from "Simon Gaiser (Qubes Security Pack signing key)" [full]
    

    Again, the exact output will differ, but the final line of output from each gpg --verify command should always start with gpg: Good signature from... followed by an appropriate key.

For this announcement (QSB-100), the commands are:

$ gpg --verify qsb-100-2024.txt.sig.marmarek qsb-100-2024.txt
$ gpg --verify qsb-100-2024.txt.sig.simon qsb-100-2024.txt

You can also verify the signatures directly from this announcement in addition to or instead of verifying the files from the qubes-secpack. Simply copy and paste the QSB-100 text into a plain text file and do the same for both signature files. Then, perform the same authentication steps as listed above, substituting the filenames above with the names of the files you just created.


This is a companion discussion topic for the original entry at https://www.qubes-os.org/news/2024/01/30/qsb-100/
1 Like