QSB-095: Missing IOMMU TLB flushing on x86 AMD systems

We have published Qubes Security Bulletin 095: Missing IOMMU TLB flushing on x86 AMD systems. 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 095


             ---===[ Qubes Security Bulletin 095 ]===---

                              2023-10-10

            Missing IOMMU TLB flushing on x86 AMD systems

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 2023-10-10, the Xen Project published XSA-442, "x86/AMD: missing
IOMMU TLB flushing" [3]:

| The caching invalidation guidelines from the AMD-Vi specification (48882—Rev
| 3.07-PUB—Oct 2022) is incorrect on some hardware, as devices will malfunction
| (see stale DMA mappings) if some fields of the DTE are updated but the IOMMU
| TLB is not flushed.
|
| Such stale DMA mappings can point to memory ranges not owned by the guest,
| thus allowing access to unindented memory regions.

Impact
-------

On affected systems, an attacker who compromises a qube with access to a PCI
device could attempt to exploit this vulnerability in order to escalate the
attacker's privileges, perform a denial-of-service (DoS) attack against the
host, and leak information. In the default Qubes OS configuration, the qubes
that have access to PCI devices are sys-net and sys-usb.

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

Only x86 AMD systems are vulnerable.

Patching
---------

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

  For Qubes 4.1, in dom0:
  - Xen packages, version 4.14.6-3

  For Qubes 4.2, in dom0:
  - Xen packages, version 4.17.2-3

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-442.html

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

Source: https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-095-2023.txt

Marek Marczykowski-Górecki’s PGP signature

-----BEGIN PGP SIGNATURE-----
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=NYhK
-----END PGP SIGNATURE-----

Source: https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-095-2023.txt.sig.marmarek

Simon Gaiser (aka HW42)’s PGP signature

-----BEGIN PGP SIGNATURE-----
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=Sojp
-----END PGP SIGNATURE-----

Source: https://github.com/QubesOS/qubes-secpack/blob/main/QSBs/qsb-095-2023.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-095), the commands are:

$ gpg --verify qsb-095-2023.txt.sig.marmarek qsb-095-2023.txt
$ gpg --verify qsb-095-2023.txt.sig.simon qsb-095-2023.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-095 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/2023/10/10/qsb-095/
2 Likes

Thanks.

Can someone explain this:

What host? dom0? Leak information from where?

I asked @marmarek about this. He replied that “host” refers to the running Qubes OS system as a whole. As for the information leak, that can be from anything running on the system.

1 Like

Thanks for taking time to both of you. Wow! I admit I’m not sure if I reviewed all 95 of QSBs, but a lot of them for sure, and I can’t remember I read anything sounding more direct and more threatening than this on the first read?

At least, it’s my first reaction on any QSB anyway…

This is a vulnerability affecting only some AMD CPUs so the impact is somewhat limited - says the guy who is not affected :sunglasses:

1 Like