Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Michal Suchánek]

Adding more CC's from the original patch, looks like get_maintainers is
not that great for this file.

On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> No other platform needs CA_MACHINE_KEYRING, either.
> 
> This is policy that should be decided by the administrator, not Kconfig
> dependencies.
> 
> cc: joeyli <jlee@suse.com>
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> ---
>  security/integrity/Kconfig | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
> index 232191ee09e3..b6e074ac0227 100644
> --- a/security/integrity/Kconfig
> +++ b/security/integrity/Kconfig
> @@ -68,8 +68,6 @@ config INTEGRITY_MACHINE_KEYRING
>  	depends on INTEGRITY_ASYMMETRIC_KEYS
>  	depends on SYSTEM_BLACKLIST_KEYRING
>  	depends on LOAD_UEFI_KEYS || LOAD_PPC_KEYS
> -	select INTEGRITY_CA_MACHINE_KEYRING if LOAD_PPC_KEYS
> -	select INTEGRITY_CA_MACHINE_KEYRING_MAX if LOAD_PPC_KEYS
>  	help
>  	 If set, provide a keyring to which Machine Owner Keys (MOK) may
>  	 be added. This keyring shall contain just MOK keys.  Unlike keys
> -- 
> 2.41.0
> 

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Nayna]

On 9/7/23 13:32, Michal Suchánek wrote:
> Adding more CC's from the original patch, looks like get_maintainers is
> not that great for this file.
>
> On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
>> No other platform needs CA_MACHINE_KEYRING, either.
>>
>> This is policy that should be decided by the administrator, not Kconfig
>> dependencies.

We certainly agree that flexibility is important. However, in this case, 
this also implies that we are expecting system admins to be security 
experts. As per our understanding, CA based infrastructure(PKI) is the 
standard to be followed and not the policy decision. And we can only 
speak for Power.

INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf 
certs.

INTEGRITY_CA_MACHINE_KEYRING_MAX ensures that CA is only allowed to do 
key signing and not code signing.

Having CA signed certs also permits easy revocation of all leaf certs.

Loading certificates is completely new for Power Systems. We would like 
to make it as clean as possible from the start. We want to enforce CA 
signed leaf certificates(INTEGRITY_CA_MACHINE_KEYRING). As per 
keyUsage(INTEGRITY_CA_MACHINE_KEYRING_MAX), if we want more flexibility, 
probably a boot time override can be considered.

Thanks & Regards,

     - Nayna


>>
>> cc: joeyli <jlee@suse.com>
>> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
>> ---
>>   security/integrity/Kconfig | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
>> index 232191ee09e3..b6e074ac0227 100644
>> --- a/security/integrity/Kconfig
>> +++ b/security/integrity/Kconfig
>> @@ -68,8 +68,6 @@ config INTEGRITY_MACHINE_KEYRING
>>   	depends on INTEGRITY_ASYMMETRIC_KEYS
>>   	depends on SYSTEM_BLACKLIST_KEYRING
>>   	depends on LOAD_UEFI_KEYS || LOAD_PPC_KEYS
>> -	select INTEGRITY_CA_MACHINE_KEYRING if LOAD_PPC_KEYS
>> -	select INTEGRITY_CA_MACHINE_KEYRING_MAX if LOAD_PPC_KEYS
>>   	help
>>   	 If set, provide a keyring to which Machine Owner Keys (MOK) may
>>   	 be added. This keyring shall contain just MOK keys.  Unlike keys
>> -- 
>> 2.41.0
>>

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Michal Suchánek]

On Mon, Sep 11, 2023 at 11:39:38PM -0400, Nayna wrote:
> 
> On 9/7/23 13:32, Michal Suchánek wrote:
> > Adding more CC's from the original patch, looks like get_maintainers is
> > not that great for this file.
> > 
> > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> > > No other platform needs CA_MACHINE_KEYRING, either.
> > > 
> > > This is policy that should be decided by the administrator, not Kconfig
> > > dependencies.
> 
> We certainly agree that flexibility is important. However, in this case,
> this also implies that we are expecting system admins to be security
> experts. As per our understanding, CA based infrastructure(PKI) is the
> standard to be followed and not the policy decision. And we can only speak
> for Power.
> 
> INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf
> certs.

And that's the problem.

From a distribution point of view there are two types of leaf certs:

 - leaf certs signed by the distribution CA which need not be imported
   because the distribution CA cert is enrolled one way or another
 - user generated ad-hoc certificates that are not signed in any way,
   and enrolled by the user

The latter are vouched for by the user by enrolling the certificate, and
confirming that they really want to trust this certificate. Enrolling
user certificates is vital for usability or secure boot. Adding extra
step of creating a CA certificate stored on the same system only
complicates things with no added benefit.

> INTEGRITY_CA_MACHINE_KEYRING_MAX ensures that CA is only allowed to do key
> signing and not code signing.
> 
> Having CA signed certs also permits easy revocation of all leaf certs.

Revocation can be also done be removing the certificate from the keyring.

If the user can add it they should also be able to remove it.

> Loading certificates is completely new for Power Systems. We would like to
> make it as clean as possible from the start. We want to enforce CA signed
> leaf certificates(INTEGRITY_CA_MACHINE_KEYRING). As per
> keyUsage(INTEGRITY_CA_MACHINE_KEYRING_MAX), if we want more flexibility,
> probably a boot time override can be considered.

If boot time override can exist it can as well be made permanent with a
Kconfig option.

I think that a boot time override is even more problematic for security
than a Kconfig option - the kernel arguments are rarely signed.

Thanks

Michal

> 
> Thanks & Regards,
> 
>     - Nayna
> 
> 
> > > 
> > > cc: joeyli <jlee@suse.com>
> > > Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> > > ---
> > >   security/integrity/Kconfig | 2 --
> > >   1 file changed, 2 deletions(-)
> > > 
> > > diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
> > > index 232191ee09e3..b6e074ac0227 100644
> > > --- a/security/integrity/Kconfig
> > > +++ b/security/integrity/Kconfig
> > > @@ -68,8 +68,6 @@ config INTEGRITY_MACHINE_KEYRING
> > >   	depends on INTEGRITY_ASYMMETRIC_KEYS
> > >   	depends on SYSTEM_BLACKLIST_KEYRING
> > >   	depends on LOAD_UEFI_KEYS || LOAD_PPC_KEYS
> > > -	select INTEGRITY_CA_MACHINE_KEYRING if LOAD_PPC_KEYS
> > > -	select INTEGRITY_CA_MACHINE_KEYRING_MAX if LOAD_PPC_KEYS
> > >   	help
> > >   	 If set, provide a keyring to which Machine Owner Keys (MOK) may
> > >   	 be added. This keyring shall contain just MOK keys.  Unlike keys
> > > -- 
> > > 2.41.0
> > > 

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Jarkko Sakkinen]

On Tue Sep 12, 2023 at 10:41 AM EEST, Michal Suchánek wrote:
> On Mon, Sep 11, 2023 at 11:39:38PM -0400, Nayna wrote:
> > 
> > On 9/7/23 13:32, Michal Suchánek wrote:
> > > Adding more CC's from the original patch, looks like get_maintainers is
> > > not that great for this file.
> > > 
> > > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> > > > No other platform needs CA_MACHINE_KEYRING, either.
> > > > 
> > > > This is policy that should be decided by the administrator, not Kconfig
> > > > dependencies.
> > 
> > We certainly agree that flexibility is important. However, in this case,
> > this also implies that we are expecting system admins to be security
> > experts. As per our understanding, CA based infrastructure(PKI) is the
> > standard to be followed and not the policy decision. And we can only speak
> > for Power.
> > 
> > INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf
> > certs.
>
> And that's the problem.
>
> From a distribution point of view there are two types of leaf certs:
>
>  - leaf certs signed by the distribution CA which need not be imported
>    because the distribution CA cert is enrolled one way or another
>  - user generated ad-hoc certificates that are not signed in any way,
>    and enrolled by the user
>
> The latter are vouched for by the user by enrolling the certificate, and
> confirming that they really want to trust this certificate. Enrolling
> user certificates is vital for usability or secure boot. Adding extra
> step of creating a CA certificate stored on the same system only
> complicates things with no added benefit.

This all comes down to the generic fact that kernel should not
proactively define what it *expects* sysadmins.

CA based infrastructure like anything is a policy decision not
a decision to be enforced by kernel.

BR, Jarkko

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Mimi Zohar]

On Tue, 2023-09-12 at 12:49 +0300, Jarkko Sakkinen wrote:
> On Tue Sep 12, 2023 at 10:41 AM EEST, Michal Suchánek wrote:
> > On Mon, Sep 11, 2023 at 11:39:38PM -0400, Nayna wrote:
> > > 
> > > On 9/7/23 13:32, Michal Suchánek wrote:
> > > > Adding more CC's from the original patch, looks like get_maintainers is
> > > > not that great for this file.
> > > > 
> > > > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> > > > > No other platform needs CA_MACHINE_KEYRING, either.
> > > > > 
> > > > > This is policy that should be decided by the administrator, not Kconfig
> > > > > dependencies.
> > > 
> > > We certainly agree that flexibility is important. However, in this case,
> > > this also implies that we are expecting system admins to be security
> > > experts. As per our understanding, CA based infrastructure(PKI) is the
> > > standard to be followed and not the policy decision. And we can only speak
> > > for Power.
> > > 
> > > INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf
> > > certs.
> >
> > And that's the problem.
> >
> > From a distribution point of view there are two types of leaf certs:
> >
> >  - leaf certs signed by the distribution CA which need not be imported
> >    because the distribution CA cert is enrolled one way or another
> >  - user generated ad-hoc certificates that are not signed in any way,
> >    and enrolled by the user
> >
> > The latter are vouched for by the user by enrolling the certificate, and
> > confirming that they really want to trust this certificate. Enrolling
> > user certificates is vital for usability or secure boot. Adding extra
> > step of creating a CA certificate stored on the same system only
> > complicates things with no added benefit.
> 
> This all comes down to the generic fact that kernel should not
> proactively define what it *expects* sysadmins.
> 
> CA based infrastructure like anything is a policy decision not
> a decision to be enforced by kernel.

Secure boot requires a signature chain of trust.  IMA extends the
secure and trusted boot concepts to the kernel. Missing from that
signature chain of trust is the ability of allowing the end
machine/system owner to load other certificates without recompiling the
kernel. The introduction of the machine keyring was to address this.

I'm not questioning the end user's intent on loading local or third
party keys via the normal mechanisms. If the existing mechanism(s) for
loading local or third party keys were full-proof, then loading a
single certificate, self-signed or not, would be fine. However, that
isn't the reality.  The security of the two-stage approach is simply
not equivalent to loading a single certificate.  Documentation could
help the end user/system owner to safely create (and manage) separate
certificate signing and code signing certs.

Unlike UEFI based systems, PowerVM defines two variables trustedcadb
and moduledb, for storing certificate signing and code signing
certificates respectively.  First the certs on the trustedcadb are
loaded and then the ones on moduledb are loaded.

-- 
thanks,

Mimi

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Jarkko Sakkinen]

On Tue Sep 12, 2023 at 10:22 PM EEST, Mimi Zohar wrote:
> On Tue, 2023-09-12 at 12:49 +0300, Jarkko Sakkinen wrote:
> > On Tue Sep 12, 2023 at 10:41 AM EEST, Michal Suchánek wrote:
> > > On Mon, Sep 11, 2023 at 11:39:38PM -0400, Nayna wrote:
> > > > 
> > > > On 9/7/23 13:32, Michal Suchánek wrote:
> > > > > Adding more CC's from the original patch, looks like get_maintainers is
> > > > > not that great for this file.
> > > > > 
> > > > > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> > > > > > No other platform needs CA_MACHINE_KEYRING, either.
> > > > > > 
> > > > > > This is policy that should be decided by the administrator, not Kconfig
> > > > > > dependencies.
> > > > 
> > > > We certainly agree that flexibility is important. However, in this case,
> > > > this also implies that we are expecting system admins to be security
> > > > experts. As per our understanding, CA based infrastructure(PKI) is the
> > > > standard to be followed and not the policy decision. And we can only speak
> > > > for Power.
> > > > 
> > > > INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf
> > > > certs.
> > >
> > > And that's the problem.
> > >
> > > From a distribution point of view there are two types of leaf certs:
> > >
> > >  - leaf certs signed by the distribution CA which need not be imported
> > >    because the distribution CA cert is enrolled one way or another
> > >  - user generated ad-hoc certificates that are not signed in any way,
> > >    and enrolled by the user
> > >
> > > The latter are vouched for by the user by enrolling the certificate, and
> > > confirming that they really want to trust this certificate. Enrolling
> > > user certificates is vital for usability or secure boot. Adding extra
> > > step of creating a CA certificate stored on the same system only
> > > complicates things with no added benefit.
> > 
> > This all comes down to the generic fact that kernel should not
> > proactively define what it *expects* sysadmins.
> > 
> > CA based infrastructure like anything is a policy decision not
> > a decision to be enforced by kernel.
>
> Secure boot requires a signature chain of trust.  IMA extends the
> secure and trusted boot concepts to the kernel. Missing from that
> signature chain of trust is the ability of allowing the end
> machine/system owner to load other certificates without recompiling the
> kernel. The introduction of the machine keyring was to address this.
>
> I'm not questioning the end user's intent on loading local or third
> party keys via the normal mechanisms. If the existing mechanism(s) for
> loading local or third party keys were full-proof, then loading a
> single certificate, self-signed or not, would be fine. However, that
> isn't the reality.  The security of the two-stage approach is simply
> not equivalent to loading a single certificate.  Documentation could
> help the end user/system owner to safely create (and manage) separate
> certificate signing and code signing certs.
>
> Unlike UEFI based systems, PowerVM defines two variables trustedcadb
> and moduledb, for storing certificate signing and code signing
> certificates respectively.  First the certs on the trustedcadb are
> loaded and then the ones on moduledb are loaded.

There's pragmatic reasons to make things more open than they should be
in production. As a hardware example I still possess Raspberry Pi 3B for
test workloads because it has a broken TZ implementation. The world is
really bigger than production workloads.

It would be better to document what you said rather than enforce the
right choice IMHO (e.g. extend Kconfig documentation).

BR, Jarkko

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Mimi Zohar]

On Tue, 2023-09-12 at 22:32 +0300, Jarkko Sakkinen wrote:
> On Tue Sep 12, 2023 at 10:22 PM EEST, Mimi Zohar wrote:
> > On Tue, 2023-09-12 at 12:49 +0300, Jarkko Sakkinen wrote:
> > > On Tue Sep 12, 2023 at 10:41 AM EEST, Michal Suchánek wrote:
> > > > On Mon, Sep 11, 2023 at 11:39:38PM -0400, Nayna wrote:
> > > > > 
> > > > > On 9/7/23 13:32, Michal Suchánek wrote:
> > > > > > Adding more CC's from the original patch, looks like get_maintainers is
> > > > > > not that great for this file.
> > > > > > 
> > > > > > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> > > > > > > No other platform needs CA_MACHINE_KEYRING, either.
> > > > > > > 
> > > > > > > This is policy that should be decided by the administrator, not Kconfig
> > > > > > > dependencies.
> > > > > 
> > > > > We certainly agree that flexibility is important. However, in this case,
> > > > > this also implies that we are expecting system admins to be security
> > > > > experts. As per our understanding, CA based infrastructure(PKI) is the
> > > > > standard to be followed and not the policy decision. And we can only speak
> > > > > for Power.
> > > > > 
> > > > > INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf
> > > > > certs.
> > > >
> > > > And that's the problem.
> > > >
> > > > From a distribution point of view there are two types of leaf certs:
> > > >
> > > >  - leaf certs signed by the distribution CA which need not be imported
> > > >    because the distribution CA cert is enrolled one way or another
> > > >  - user generated ad-hoc certificates that are not signed in any way,
> > > >    and enrolled by the user
> > > >
> > > > The latter are vouched for by the user by enrolling the certificate, and
> > > > confirming that they really want to trust this certificate. Enrolling
> > > > user certificates is vital for usability or secure boot. Adding extra
> > > > step of creating a CA certificate stored on the same system only
> > > > complicates things with no added benefit.
> > > 
> > > This all comes down to the generic fact that kernel should not
> > > proactively define what it *expects* sysadmins.
> > > 
> > > CA based infrastructure like anything is a policy decision not
> > > a decision to be enforced by kernel.
> >
> > Secure boot requires a signature chain of trust.  IMA extends the
> > secure and trusted boot concepts to the kernel. Missing from that
> > signature chain of trust is the ability of allowing the end
> > machine/system owner to load other certificates without recompiling the
> > kernel. The introduction of the machine keyring was to address this.
> >
> > I'm not questioning the end user's intent on loading local or third
> > party keys via the normal mechanisms. If the existing mechanism(s) for
> > loading local or third party keys were full-proof, then loading a
> > single certificate, self-signed or not, would be fine. However, that
> > isn't the reality.  The security of the two-stage approach is simply
> > not equivalent to loading a single certificate.  Documentation could
> > help the end user/system owner to safely create (and manage) separate
> > certificate signing and code signing certs.
> >
> > Unlike UEFI based systems, PowerVM defines two variables trustedcadb
> > and moduledb, for storing certificate signing and code signing
> > certificates respectively.  First the certs on the trustedcadb are
> > loaded and then the ones on moduledb are loaded.
> 
> There's pragmatic reasons to make things more open than they should be
> in production. As a hardware example I still possess Raspberry Pi 3B for
> test workloads because it has a broken TZ implementation. The world is
> really bigger than production workloads.
> 
> It would be better to document what you said rather than enforce the
> right choice IMHO (e.g. extend Kconfig documentation).

PowerVM LPARs are more about production workloads than a Raspberry Pi. 
:)

-- 
thanks,

Mimi

Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

[Jarkko Sakkinen]

On Tue Sep 12, 2023 at 6:39 AM EEST, Nayna wrote:
>
> On 9/7/23 13:32, Michal Suchánek wrote:
> > Adding more CC's from the original patch, looks like get_maintainers is
> > not that great for this file.
> >
> > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> >> No other platform needs CA_MACHINE_KEYRING, either.
> >>
> >> This is policy that should be decided by the administrator, not Kconfig
> >> dependencies.
>
> We certainly agree that flexibility is important. However, in this case, 
> this also implies that we are expecting system admins to be security 
> experts. As per our understanding, CA based infrastructure(PKI) is the 
> standard to be followed and not the policy decision. And we can only 
> speak for Power.

In the end this is dictating policy for no compelling reason, and
that is the bottom line here, not playing a mind game what type of
expertise a sysadmin might or might not have.

BR, Jarkko