| Message ID | 20210907160110.2699645-1-eric.snowberg@oracle.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Enroll kernel keys thru MOK | expand |
On Tue, 2021-09-07 at 12:00 -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 What exactly is "trust boundary"? And what do you mean when you say that Linux "trusts" something? AFAIK, software does not have feelings. Please, just speak about exact things. That's the whole point of the cover letter. It's better to not have cover letter at all, than a confusing cover letter that reads like a white paper. Code changes at least tell the exact story, and not speak about feelings. > 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. I use a pre-compiled kernel in my desktop: https://liquorix.net/. When a new version comes up it requires a sbsign one-liner to sign it for secure boot. I'm wondering what is the problem I'm facing because I do not see it. If there are something missing changes that you use as a rationale for this large patch set, you should at least broadly explain what we are missing. How I conclude this paragraph is that, since there is only an xref, they are not really "that important" changes, which are missing. > 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 Which both can be done by end-user as of today, or I'm misreading this. > 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. What is IMA appraisal? I just don't know it because I don't use IMA. Again, this trust boundary is really something I do not. Looking at code changes, you could just speak about exact assets in the kernel. > Downstream Linux distros try to have a single signed kernel for each > architecture. Each end-user may use this kernel in entirely different > ways. Some downstream kernels have chosen to always trust platform keys > within the Linux trust boundary for kernel module signing. These > kernels have no way of using digital signature base IMA appraisal. > > This series introduces a new Linux kernel keyring containing the Machine > Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim. > This variable allows the end-user to decide if they want to trust keys > enrolled in the MOK within the Linux trust boundary. By default, > nothing changes; MOK keys are not trusted within the Linux kernel. They > are only trusted after the end-user makes the decision themselves. The > end-user would set this through mokutil using a new --trust-mok option > [3]. This would work similar to how the kernel uses MOK variables to > enable/disable signature validation as well as use/ignore the db. OK, changes are described here (again speaking about trusting tho). The motivation part is missing. The text before this is more like confusion part. When you describe motivation to do something you should really be in grass roots, e.g. "when you have this feature in the kernel, look, I can do now this". It's not that hard. E.g. with an usage example it is quite quick accomplish this. /Jarkko
On Wed, 2021-09-08 at 19:03 +0300, Jarkko Sakkinen wrote: > On Tue, 2021-09-07 at 12:00 -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 > > What exactly is "trust boundary"? And what do you mean when you say that > Linux "trusts" something? AFAIK, software does not have feelings. Please, > just speak about exact things. > > That's the whole point of the cover letter. It's better to not have cover > letter at all, than a confusing cover letter that reads like a white paper. > Code changes at least tell the exact story, and not speak about feelings. > > > 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. > > I use a pre-compiled kernel in my desktop: https://liquorix.net/. When > a new version comes up it requires a sbsign one-liner to sign it for > secure boot. I'm wondering what is the problem I'm facing because I do > not see it. > > If there are something missing changes that you use as a rationale for > this large patch set, you should at least broadly explain what we are > missing. How I conclude this paragraph is that, since there is only an > xref, they are not really "that important" changes, which are missing. > > > 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 > > Which both can be done by end-user as of today, or I'm misreading this. > > > 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. > > What is IMA appraisal? I just don't know it because I don't use IMA. > Again, this trust boundary is really something I do not. Looking at > code changes, you could just speak about exact assets in the kernel. > > > Downstream Linux distros try to have a single signed kernel for each > > architecture. Each end-user may use this kernel in entirely different > > ways. Some downstream kernels have chosen to always trust platform keys > > within the Linux trust boundary for kernel module signing. These > > kernels have no way of using digital signature base IMA appraisal. > > > > This series introduces a new Linux kernel keyring containing the Machine > > Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim. > > This variable allows the end-user to decide if they want to trust keys > > enrolled in the MOK within the Linux trust boundary. By default, > > nothing changes; MOK keys are not trusted within the Linux kernel. They > > are only trusted after the end-user makes the decision themselves. The > > end-user would set this through mokutil using a new --trust-mok option > > [3]. This would work similar to how the kernel uses MOK variables to > > enable/disable signature validation as well as use/ignore the db. > > OK, changes are described here (again speaking about trusting tho). The > motivation part is missing. The text before this is more like confusion > part. When you describe motivation to do something you should really be in > grass roots, e.g. "when you have this feature in the kernel, look, I can > do now this". It's not that hard. E.g. with an usage example it is quite > quick accomplish this. The code changes overally make sense but this motivotional part is the problem. E.g. if you do a pull request, it is completely *unusable* in that context. In that case I would have to write something that should have been the cover letter. It's 12 patches, so it is perfectly sensible to ask a better one. /Jarkko
> On Sep 8, 2021, at 10:03 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote: > > On Tue, 2021-09-07 at 12:00 -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 > > What exactly is "trust boundary"? And what do you mean when you say that > Linux "trusts" something? AFAIK, software does not have feelings. Please, > just speak about exact things. I am using terminology used previously by others when addressing this issue. If I should be using different terminology, please advise. The kernel does not trust pre-boot keys within it, meaning these pre-boot keys can not be used to validate items within the kernel. This is the “trust boundary”. Preboot keys are on one side of the boundary, compiled-in keys are on the other. MOK keys are pre-boot keys. Currently they can not be used to validate things within the kernel itself (kernel modules, IMA keys, etc).
> On Sep 8, 2021, at 10:49 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote: > > On Wed, 2021-09-08 at 19:03 +0300, Jarkko Sakkinen wrote: >> >>> Downstream Linux distros try to have a single signed kernel for each >>> architecture. Each end-user may use this kernel in entirely different >>> ways. Some downstream kernels have chosen to always trust platform keys >>> within the Linux trust boundary for kernel module signing. These >>> kernels have no way of using digital signature base IMA appraisal. >>> >>> This series introduces a new Linux kernel keyring containing the Machine >>> Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim. >>> This variable allows the end-user to decide if they want to trust keys >>> enrolled in the MOK within the Linux trust boundary. By default, >>> nothing changes; MOK keys are not trusted within the Linux kernel. They >>> are only trusted after the end-user makes the decision themselves. The >>> end-user would set this through mokutil using a new --trust-mok option >>> [3]. This would work similar to how the kernel uses MOK variables to >>> enable/disable signature validation as well as use/ignore the db. >> >> OK, changes are described here (again speaking about trusting tho). The >> motivation part is missing. The text before this is more like confusion >> part. When you describe motivation to do something you should really be in >> grass roots, e.g. "when you have this feature in the kernel, look, I can >> do now this". It's not that hard. E.g. with an usage example it is quite >> quick accomplish this. > > The code changes overally make sense but this motivotional part is the > problem. E.g. if you do a pull request, it is completely *unusable* in > that context. In that case I would have to write something that should > have been the cover letter. It's 12 patches, so it is perfectly sensible > to ask a better one. Would this be a more appropriate cover letter that includes a better motivation? Back in 2013 Linus requested a feature to allow end-users to have the ability "to add their own keys and sign modules they trust". This was his *second* order outlined here [1]. There have been many attempts over the years to solve this problem, all have been rejected. Many distributions carry one of these rejected attempts. This series tries to solve this problem with a solution that takes into account all the problems brought up in the previous attempts. This series introduces a new Linux kernel keyring containing the Machine Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim. This variable allows the end-user to decide if they want to load keys enrolled in the MOK within the Linux kernel. By default, nothing changes; MOK keys are not loaded within the Linux kernel. They are only loaded after the end-user makes the decision themselves. The end-user would set this through mokutil using a new --trust-mok option [2]. This would work similar to how the kernel uses MOK variables to enable/disable signature validation as well as use/ignore the db. Mimi has suggested that only CA keys be loaded into this keyring. All other certs will load into the platform keyring instead. Secure Boot keys will never be loaded. They will always be loaded into the platform keyring. If an end-user wanted to load one, they would need to enroll it into the MOK. Steps required by the end user: Sign kernel module with user created key: $ /usr/src/kernels/$(uname -r)/scripts/sign-file sha512 signing_key.priv \ signing_key.x509 my_module.ko Import the key into the MOK $ mokutil --import signing_key.x509 Setup the kernel to load MOK keys into the .machine keyring $ mokutil —trust-mok Then reboot, the MokManager will load and ask if you want to trust the MOK key and enroll the MOK into the MOKList. Afterwards the signed kernel module will load. I have included links to both the mokutil [2] and shim [3] changes I have made to support this new functionality. [1] https://marc.info/?l=linux-kernel&m=136185386310140&w=2 [2] https://github.com/esnowberg/mokutil/tree/0.3.0-mokvars-v2 [3] https://github.com/esnowberg/shim/tree/mokvars-v2
On Wed, 2021-09-08 at 16:25 -0600, Eric Snowberg wrote: > > On Sep 8, 2021, at 10:49 AM, Jarkko Sakkinen <jarkko@kernel.org> wrote: > > > > On Wed, 2021-09-08 at 19:03 +0300, Jarkko Sakkinen wrote: > >> > >>> Downstream Linux distros try to have a single signed kernel for each > >>> architecture. Each end-user may use this kernel in entirely different > >>> ways. Some downstream kernels have chosen to always trust platform keys > >>> within the Linux trust boundary for kernel module signing. These > >>> kernels have no way of using digital signature base IMA appraisal. > >>> > >>> This series introduces a new Linux kernel keyring containing the Machine > >>> Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim. > >>> This variable allows the end-user to decide if they want to trust keys > >>> enrolled in the MOK within the Linux trust boundary. By default, > >>> nothing changes; MOK keys are not trusted within the Linux kernel. They > >>> are only trusted after the end-user makes the decision themselves. The > >>> end-user would set this through mokutil using a new --trust-mok option > >>> [3]. This would work similar to how the kernel uses MOK variables to > >>> enable/disable signature validation as well as use/ignore the db. > >> > >> OK, changes are described here (again speaking about trusting tho). The > >> motivation part is missing. The text before this is more like confusion > >> part. When you describe motivation to do something you should really be in > >> grass roots, e.g. "when you have this feature in the kernel, look, I can > >> do now this". It's not that hard. E.g. with an usage example it is quite > >> quick accomplish this. > > > > The code changes overally make sense but this motivotional part is the > > problem. E.g. if you do a pull request, it is completely *unusable* in > > that context. In that case I would have to write something that should > > have been the cover letter. It's 12 patches, so it is perfectly sensible > > to ask a better one. > > Would this be a more appropriate cover letter that includes a better > motivation? > > Back in 2013 Linus requested a feature to allow end-users to have the > ability "to add their own keys and sign modules they trust". This was his > *second* order outlined here [1]. There have been many attempts over the > years to solve this problem, all have been rejected. Many distributions > carry one of these rejected attempts. This series tries to solve this problem > with a solution that takes into account all the problems brought up in the > previous attempts. Instead of making the reviewer look up the failed attempts, please summarize why they failed (e.g. all preboot firmware keys were trusted), and then continue, like below, with how this attempt differs. > > This series introduces a new Linux kernel keyring containing the Machine > Owner Keys (MOK) called .machine. Other archs will also want to allow loading "end-users" key. Please prefix this paragraph with something like "On UEFI based systems". > It also adds a new MOK variable to shim. Replace "adds" with "defines". > This variable allows the end-user to decide if they want to load keys > enrolled in the MOK within the Linux kernel. By default, nothing changes; > MOK keys are not loaded within the Linux kernel. They are only loaded after > the end-user makes the decision themselves. The end-user would set this > through mokutil using a new --trust-mok option [2]. This would work similar > to how the kernel uses MOK variables to enable/disable signature validation > as well as use/ignore the db. Mimi has suggested that only CA keys be loaded > into this keyring. All other certs will load into the platform keyring instead. Thank you for crediting me for limiting loading only the CA keys stored in the MOK db onto the "machine" keyring, but the limitation should be better integrated in the paragraph. > Secure Boot keys will never be loaded. They will always be loaded into > the platform keyring. If an end-user wanted to load one, they would > need to enroll it into the MOK. > > Steps required by the end user: > > Sign kernel module with user created key: > $ /usr/src/kernels/$(uname -r)/scripts/sign-file sha512 signing_key.priv \ > signing_key.x509 my_module.ko > > Import the key into the MOK > $ mokutil --import signing_key.x509 To differentiate this "signing_key" from others, perhaps name the file "machine_sigining_key" or "local_signing_key". thanks, Mimi > > Setup the kernel to load MOK keys into the .machine keyring > $ mokutil —trust-mok > > Then reboot, the MokManager will load and ask if you want to trust the MOK > key and enroll the MOK into the MOKList. Afterwards the signed kernel module > will load. > > I have included links to both the mokutil [2] and shim [3] changes I > have made to support this new functionality. > > [1] https://marc.info/?l=linux-kernel&m=136185386310140&w=2 > [2] https://github.com/esnowberg/mokutil/tree/0.3.0-mokvars-v2 > [3] https://github.com/esnowberg/shim/tree/mokvars-v2
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. Downstream Linux distros try to have a single signed kernel for each architecture. Each end-user may use this kernel in entirely different ways. Some downstream kernels have chosen to always trust platform keys within the Linux trust boundary for kernel module signing. These kernels have no way of using digital signature base IMA appraisal. This series introduces a new Linux kernel keyring containing the Machine Owner Keys (MOK) called .machine. It also adds a new MOK variable to shim. This variable allows the end-user to decide if they want to trust keys enrolled in the MOK within the Linux trust boundary. By default, nothing changes; MOK keys are not trusted within the Linux kernel. They are only trusted after the end-user makes the decision themselves. The end-user would set this through mokutil using a new --trust-mok option [3]. This would work similar to how the kernel uses MOK variables to enable/disable signature validation as well as use/ignore the db. When shim boots, it mirrors the new MokTML Boot Services variable to a new MokListTrustedRT Runtime Services variable and extends PCR14. MokListTrustedRT is written without EFI_VARIABLE_NON_VOLATILE set, preventing an end-user from setting it after booting and doing a kexec. When the kernel boots, if MokListTrustedRT is set and EFI_VARIABLE_NON_VOLATILE is not set, the MokListRT is loaded into the machine keyring instead of the platform keyring. Mimi has suggested that only CA keys be loaded into this keyring. All other certs will load into the platform keyring instead. The machine keyring contains a new keyring permission that only allows CA keys to be loaded. If the permission fails, the key is later loaded into the platform keyring. After all keys are added into the machine keyring, they are linked to the secondary trusted keyring. After the link is created, keys contained in the machine keyring will automatically be searched when searching the secondary trusted keys. Secure Boot keys will never be trusted. They will always be loaded into the platform keyring. If an end-user wanted to trust one, they would need to enroll it into the MOK. I have included links to both the mokutil [3] and shim [4] changes I have made to support this new functionality. V2 changes: - The .mok keyring persists past boot - Removed the unrestricted move into the secondary keyring - Removed the keyring move bypass patch - Added restrictions to allow the .mok to be linked to either the builtin or secondary keyrings - Secondary keyring dependency has been removed V3 changes: - Only CA keys contained in the MOKList are loaded, nothing else - Support for kernels built without the secondary trusted keyring has been dropped. V4 changes: - Add new Kconfig INTEGRITY_MOK_KEYRING and move all mok keyring code behind it - Changed patch series ordering - Consolidated a few patches V5 changes: - Rename from mok keyring to machine keyring [1] https://lore.kernel.org/lkml/1556221605.24945.3.camel@HansenPartnership.com/ [2] https://lore.kernel.org/patchwork/cover/902768/ [3] https://github.com/esnowberg/mokutil/tree/0.3.0-mokvars-v2 [4] https://github.com/esnowberg/shim/tree/mokvars-v2 Eric Snowberg (12): integrity: Introduce a Linux keyring called machine integrity: Do not allow machine keyring updates following init KEYS: CA link restriction integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca integrity: add new keyring handler for mok keys KEYS: add a reference to machine keyring KEYS: Introduce link restriction to include builtin, secondary and machine keys KEYS: integrity: change link restriction to trust the machine keyring KEYS: link secondary_trusted_keys to machine trusted keys integrity: store reference to machine keyring integrity: Trust MOK keys if MokListTrustedRT found integrity: Only use machine keyring when uefi_check_trust_mok_keys is true certs/system_keyring.c | 40 ++++++++- crypto/asymmetric_keys/restrict.c | 40 +++++++++ include/crypto/public_key.h | 5 ++ include/keys/system_keyring.h | 14 +++ security/integrity/Kconfig | 11 +++ security/integrity/Makefile | 1 + security/integrity/digsig.c | 18 +++- security/integrity/integrity.h | 17 +++- .../platform_certs/keyring_handler.c | 17 +++- .../platform_certs/keyring_handler.h | 5 ++ security/integrity/platform_certs/load_uefi.c | 4 +- .../platform_certs/machine_keyring.c | 85 +++++++++++++++++++ 12 files changed, 249 insertions(+), 8 deletions(-) create mode 100644 security/integrity/platform_certs/machine_keyring.c base-commit: e22ce8eb631bdc47a4a4ea7ecf4e4ba499db4f93