On Thu, 2021-08-19 at 09:10 -0400, Mimi Zohar wrote: > On Thu, 2021-08-19 at 14:38 +0300, Jarkko Sakkinen wrote: > > On Wed, 2021-08-18 at 20:20 -0400, Eric Snowberg wrote: > > > Many UEFI Linux distributions boot using shim. The UEFI shim provides > > > what is called Machine Owner Keys (MOK). Shim uses both the UEFI Secure > > > Boot DB and MOK keys to validate the next step in the boot chain. The > > > MOK facility can be used to import user generated keys. These keys can > > > be used to sign an end-user development kernel build. When Linux boots, > > > pre-boot keys (both UEFI Secure Boot DB and MOK keys) get loaded in the > > > Linux .platform keyring. > > > > > > Currently, pre-boot keys are not trusted within the Linux trust boundary > > > [1]. These platform keys can only be used for kexec. If an end-user > > > wants to use their own key within the Linux trust boundary, they must > > > either compile it into the kernel themselves or use the insert-sys-cert > > > script. Both options present a problem. Many end-users do not want to > > > compile their own kernels. With the insert-sys-cert option, there are > > > missing upstream changes [2]. Also, with the insert-sys-cert option, > > > the end-user must re-sign their kernel again with their own key, and > > > then insert that key into the MOK db. Another problem with > > > insert-sys-cert is that only a single key can be inserted into a > > > compressed kernel. > > > > > > Having the ability to insert a key into the Linux trust boundary opens > > > up various possibilities. The end-user can use a pre-built kernel and > > > sign their own kernel modules. It also opens up the ability for an > > > end-user to more easily use digital signature based IMA-appraisal. To > > > get a key into the ima keyring, it must be signed by a key within the > > > Linux trust boundary. > > > > As of today, I can use a prebuilt kernel, crate my own MOK key and sign > > modules. What will be different? > > The UEFI db and MOK keys are being loaded onto the .platform keyring, > which is suppose to be limited to verifying the kexec kernel image > signature. With a downstream patch, kernel modules are being verified > as well. > > Initially Patrick Uiterwijk's "[PATCH 0/3] Load keys from TPM2 NV Index > on IMA keyring" patch set attempted to define a new root of trust based > on a key stored in the TPM. This patch set is similarly attempting to > define a new root of trust based on CA keys stored in the MOK db. > > The purpose of this patch set is to define a new, safe trust source > parallel to the builtin keyring, without relying on a downstream patch. > With the new root of trust, the end user could sign his own kernel > modules, sign third party keys, and load keys onto the IMA keyring, > which can be used for signing the IMA policy and other files. I can, as of today, generate my own mok key and sign my LKM's, and kernel will verify my LKM's. What is different? /Jarkko
