On Thu, 2022-12-15 at 20:28 +0000, Eric Snowberg wrote: > > > On Dec 15, 2022, at 12:58 PM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > > > > On Thu, 2022-12-15 at 16:26 +0000, Eric Snowberg wrote: > >> > >>> On Dec 15, 2022, at 3:21 AM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote: > >>> > >>> On Tue, 2022-12-13 at 19:33 -0500, Eric Snowberg wrote: > >>>> Prior to the introduction of the machine keyring, most distros simply > >>>> allowed all keys contained within the platform keyring to be used > >>>> for both kernel and module verification. This was done by an out of > >>>> tree patch. Some distros took it even further and loaded all these keys > >>>> into the secondary trusted keyring. This also allowed the system owner > >>>> to add their own key for IMA usage. > >>>> > >>>> Each distro contains similar documentation on how to sign kernel modules > >>>> and enroll the key into the MOK. The process is fairly straightforward. > >>>> With the introduction of the machine keyring, the process remains > >>>> basically the same, without the need for any out of tree patches. > >>>> > >>>> The machine keyring allowed distros to eliminate the out of tree patches > >>>> for kernel module signing. However, it falls short in allowing the end > >>>> user to add their own keys for IMA. Currently the machine keyring can not > >>>> be used as another trust anchor for adding keys to the ima keyring, since > >>>> CA enforcement does not currently exist. This would expand the current > >>>> integrity gap. The IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY > >>>> Kconfig states that keys may be added to the ima keyrings if the key is > >>>> validly signed by a CA cert in the system built-in or secondary trusted > >>>> keyring. Currently there is not code that enforces the contents of a > >>>> CA cert. Any key in the builtin or secondary keyring can be used. > >>>> > >>>> To allow IMA to be enabled with the machine keyring, this series introduces > >>>> enforcement of key usage in the certificate. This series also applies > >>>> this enforcement across all kernel keyrings. > >>>> > >>>> The machine keyring shares similarities with both the builtin and > >>>> secondary keyrings. Similar to the builtin, no keys may be added to the > >>>> machine keyring following boot. The secondary keyring allows user > >>>> provided keys to be added following boot; however, a previously enrolled > >>>> kernel key must vouch for the key before it may be included. The system > >>>> owner may include their own keys into the machine keyring prior to boot. > >>>> If the end-user is not the system owner, they may not add their own keys > >>>> to the machine keyring. > >>>> > >>>> The machine keyring is only populated when Secure Boot is enabled. A > >>>> system owner has the ability to control the entire Secure Boot keychain > >>>> (PK, KEK, DB, and DBX). The system owner can also turn Secure Boot off. > >>>> With this control, they may use insert-sys-cert to include their own key > >>>> and re-sign their kernel and have it boot. The system owner also has > >>>> control to include or exclude MOK keys. This series does not try to > >>>> interpret how a system owner has configured their machine. If the system > >>>> owner has taken the steps to add their own MOK keys, they will be > >>>> included in the machine keyring and used for verification, exactly > >>>> the same way as keys contained in the builtin and secondary keyrings. > >>>> Since the system owner has the ability to add keys before booting to > >>>> either the machine or builtin keyrings, it is viewed as inconsequential > >>>> if the key originated from one or the other. > >>>> > >>>> This series introduces two different ways to configure the machine keyring. > >>>> By default, nothing changes and all MOK keys are loaded into it. Whenever > >>>> a CA cert is found within the machine, builtin, or secondary, a flag > >>>> indicating this is stored in the public key struct. The other option is > >>>> if the new Kconfig INTEGRITY_CA_MACHINE_KEYRING is enabled, only CA certs > >>>> will be loaded into the machine keyring. All remaining MOK keys will be > >>>> loaded into the platform keyring. > >>>> > >>>> A CA cert shall be defined as any X509 certificate that contains the > >>>> keyCertSign key usage and has the CA bit set to true. > >>> > >>> Hi Eric, > >>> > >>> Allowing CA certificates with the digitalSignature key usage flag > >>> enabled defeats the purpose of the new Kconfig. Please update the > >>> above definition to exclude the digitalSignature key usage flag and > >>> modify the code accordingly. > >> > >> Within v2, the request was made to allow Intermediate CA certificates to be > >> loaded directly. The Intermediate CA referenced was the one used by kernel.org. > >> This Intermediate CA contains both digitalSignature and keyCertSign. If the code > >> is changed to exclude this certificate, now the root CA has to be loaded again. Is that > >> the intent? > > > > That definitely was not the intent. Nor would it address the issue of > > a particular intermediate CA certificate having both keyCertSign and > > digitalSignature. > > Sorry, I’m not following. Why is it an issue that an intermediate CA certificate contains > both keyCertSign and digitalSignature? Why would we want to exclude an Intermediate > CA cert like the one used on kernel.org? I must be missing something. Isn't the purpose of "keyUsage" to minimize how a certificate may be used? Why would we want the same certificate to be used for both certificate signing and code signing? thanks, Mimi
