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Bug#960195: linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y

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  Bug#960195: linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y Timo Lindfors <timo.lindfors@iki.fi> - 2020-05-10 16:10 +0200
    Bug#960195: #960195 linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y Timo Lindfors <timo.lindfors@iki.fi> - 2020-10-26 17:50 +0100
    Bug#960195: marked as done (linux-image-5.6.0-1-amd64: Please  enable CONFIG_INTEL_TXT=y) "Debian Bug Tracking System" <owner@bugs.debian.org> - 2020-12-17 13:10 +0100

#67051 — Bug#960195: linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y

Package: src:linux
Version: 5.6.7-1
Severity: wishlist

Hi,

can you please enable CONFIG_INTEL_TXT=y on x86? I am in the process
of packaging tboot for Debian (#803180) and it would be nice if users
would not need to rebuild their kernels for this.

I have used Debian kernels rebuilt with CONFIG_INTEL_TXT=y on both
servers and laptops for around three years now without noticing any
drawbacks at all.

Here's a work-in-progress README.Debian file for tboot that might give
you some perspective on how tboot is used.


tboot for Debian
---------------

Background
----------

Trusted computing is a broad and complex topic but here is a short
summary on how tboot fits to the picture.

There are two main ways of performing measured boot. In SRTM (Static
Root of Trust Measurement) each component measures the subsequent
component in the boot chain to the TPM chip. The TPM chip cannot stop
the boot process but you can store secrets (e.g. disk encryption keys)
to the TPM such that they can only be accessed if the TPM has observed
unmodified measurements of the boot chain.

In DRTM (Dynamic Root of Trust Measurement) a special CPU instruction
(SENTER) is used to enter a measured launch environment that cannot be
affected by the software that was running earlier during the boot
process. Similarly to SRTM this environment is measured to the
TPM. The main benefit of DRTM is that bugs in your BIOS or boot loader
cannot be used to send fake measurements to the TPM. The main
drawbacks are that it requires a CPU that supports the SENTER
instruction and that it is vulnerable to malicious code running in SMM
(System Management Mode) or ME (Management Engine).

It is possible to combine SRTM and DRTM. It is also possible to use
them together with Secure Boot to prevent loading untrusted code.

The tpm.mod module in the Debian package grub-efi-amd64-bin can be
used for SRTM. This package can be used for DRTM.

AMD has its own instruction for DRTM, called SKINIT, but tboot does
not support it at the moment.

Getting started
---------------

If you want to boot Linux with tboot you need a kernel built with
CONFIG_INTEL_TXT=y. Currently Debian kernels are not built with this
option so you need to rebuild the kernel. One way to do that is as
follows:

1) $ sudo apt-get install devscripts
2) $ apt-get source linux
3) Edit debian/config/config and add CONFIG_INTEL_TXT=y
4) Edit debian/config/defines and add "+txt.1" to abiname. If you
    don't need real-time kernels and want to save build-time you can also
    set "enabled: false" for featureset-rt_base
5) $ dch -i
6) Add "+txt.1" to the version number and save the file.
7) $ sudo apt-get build-dep linux
8) $ env DEB_BUILD_OPTIONS="parallel=$(nproc)" dpkg-buildpackage 
-rfakeroot -us -uc
9) Run the previous command again since it intentionally fails on the
    first run. The build should take around 2-3 hours.

Note that you also either need to specify the boot option
intel_iommu=on or use a kernel that has
CONFIG_INTEL_IOMMU_DEFAULT_ON=y set.

The boot firmware should provide the ACMs (authenticated code modules)
needed for Intel TXT to function. If the boot firmware does not do
this then it might still be possible to use TXT if tboot loads the ACM
modules from the filesystem. These ACM modules are non-free and not
recommended. For more information, see for example
https://doc.coreboot.org/security/intel/acm.html

Common misconfigurations
------------------------

This package does not provide a complete solution for e.g. TPM-based
disk encryption. However, regardless of what solution you end up using
you should make sure that it avoids at least the following common
misconfigurations:

1) If you use a normal Debian initramfs you can easily get a root
    shell without affecting TPM measurements e.g. by disconnecting the
    hard disk during the boot process. One way to solve this issue is
    to use the boot parameter panic=86400.

2) If you use LVM inside your encrypted LUKS volume it is possible to
    trick LVM into activating an LVM PV from unencrypted media. If you
    provide your own /sbin/init on that media you can execute arbitrary
    code as root. One way to solve this to use e.g.

    filter = [ "a|/dev/mapper/md1_crypt|" ]

    in /etc/lvm/lvm.conf.

3) If you use an UUID or GUID to find the root partition an attacker
    can similarly trick the boot process into running their own
    /sbin/init. The default configuration in Debian with LVM on LUKS
    avoids this issue by specifying the boot parameter
    root=/dev/mapper/HOSTNAME--vg-root.

4) It is possible to trick systemd-gpt-auto-generator into activating
    an unencrypted swap device and mounting an unencrypted /srv
    partition. This can lead into arbitrary code execution.  One way to
    solve this problem is to use the boot parameter
    systemd.gpt_auto=no.

5) An attacker can tamper with the files that are stored on the
    unencrypted /boot partition. If you support automatic updates with
    forward-sealing of data for new package versions there is a risk
    that you might seal data for tampered system files. A solution is
    to carefully verify the integrity of files used for measurements
    and to force any generated files to be regenerated. One way to
    implement this is to use the following commands:

    (cd / && grep -h " boot/" /var/lib/dpkg/info/*md5sums | md5sum -c)
    update-initramfs -k all -d
    update-initramfs -k all -c
    update-grub2




-Timo

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#68446 — Bug#960195: #960195 linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y

Hi,

tboot is now in testing, is there anything I could do to make it easier to 
enable this config option in src:linux? It's such hassle for the sysadmin 
to build their own kernels that it would be really nice to be able to use 
tboot with official Debian kernels. (It would be especially nice since the 
cryptographic hashes would be verifiable by a third-party more easily).

-Timo

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#68902 — Bug#960195: marked as done (linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y)

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Your message dated Thu, 17 Dec 2020 12:00:09 +0000
with message-id <E1kprx3-0008yY-Tv@fasolo.debian.org>
and subject line Bug#960195: fixed in linux 5.10.1-1~exp1
has caused the Debian Bug report #960195,
regarding linux-image-5.6.0-1-amd64: Please enable CONFIG_INTEL_TXT=y
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact owner@bugs.debian.org
immediately.)


-- 
960195: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=960195
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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