On Thu, 2013-10-31 at 14:23 +0200, Dmitry Kasatkin wrote:
> On 31/10/13 14:03, Mimi Zohar wrote:
> > On Thu, 2013-10-31 at 10:30 +0200, Dmitry Kasatkin wrote:
> >> On 30/10/13 20:54, Mimi Zohar wrote:
> >>> Require all keys added to the IMA keyring be signed by an
> >>> existing trusted key on the system trusted keyring.
> >>>
> >>> Changelog:
> >>> - define stub integrity_init_keyring() function (reported-by Fengguang Wu)
> >>> - differentiate between regular and trusted keyring names.
> >>> - replace printk with pr_info (D. Kasatkin)
> >>>
> >>> Signed-off-by: Mimi Zohar <zo...@us.ibm.com>
> >>> ---
> >>> security/integrity/digsig.c | 30 +++++++++++++++++++++++++++++-
> >>> security/integrity/ima/Kconfig | 8 ++++++++
> >>> security/integrity/ima/ima_appraise.c | 11 +++++++++++
> >>> security/integrity/integrity.h | 7 +++++++
> >>> 4 files changed, 55 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/security/integrity/digsig.c b/security/integrity/digsig.c
> >>> index b4af4eb..77ca965 100644
> >>> --- a/security/integrity/digsig.c
> >>> +++ b/security/integrity/digsig.c
> >>> @@ -13,7 +13,9 @@
> >>> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> >>>
> >>> #include <linux/err.h>
> >>> +#include <linux/sched.h>
> >>> #include <linux/rbtree.h>
> >>> +#include <linux/cred.h>
> >>> #include <linux/key-type.h>
> >>> #include <linux/digsig.h>
> >>>
> >>> @@ -21,11 +23,19 @@
> >>>
> >>> static struct key *keyring[INTEGRITY_KEYRING_MAX];
> >>>
> >>> +#ifdef CONFIG_IMA_TRUSTED_KEYRING
> >>> +static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
> >>> + ".evm",
> >>> + ".module",
> >>> + ".ima",
> >>> +};
> >>> +#else
> >>> static const char *keyring_name[INTEGRITY_KEYRING_MAX] = {
> >>> "_evm",
> >>> "_module",
> >>> "_ima",
> >>> };
> >>> +#endif
> >> Hello,
> >>
> >> I am not sure if having 2 different names "_" and "." makes sense.
> > The existing keyring implementation permits userspace to create a new
> > keyring with the exact same name as a previously defined trusted
> > keyring. For all practical purposes, replacing a trusted keyring with
> > an untrusted one. The existing solution is to prohibit userspace from
> > creating a dot prefixed keyring.
> >
> > Allowing only signed keys to be added to the IMA keyring breaks the
> > existing userspace/kernel ABI, which has existed since linux-3.3. At
> > some point, we could deprecate the non trusted keyring.
> >
> >> Setting trusted-only makes sense until we will get support of setting
> >> trusted only from user-space using keyctl...
> > Agreed, userspace should be permitted to create a trusted keyring, but
> > not change an existing keyring to trusted.
>
> Then all keys on that keyring must be signed..
> This is not what I was saying...
>
> It is always possible to specify keyring hierarchy and rules what
> verifies what.
> But may be better not to over-engineer...
>
> It is how it is now.. Will see based on use-cases in the future...
Right, keys can be loaded onto the existing keyring; and the keyring can
be locked in the initramfs. Moving forward, a trusted keyring implies a
HW based certificate chain of trust.
> >> David, do you remember our discussion in Edinburgh?
> >> Can you provide a way to set keyring as trusted-only from user space..
> >>
> >> Motivation...
> >>
> >> In many embedded systems, initramfs is built into the kernel image.
> >> Kernel image is signed and obviously initramfs as well..
> >> Or initramfs may be signed separately like in my prototype
> >> implementation...
> >> Note that non-x86 systems - embedded, mobile, etc has no UEFI, MOK.
> >> Initial keys cannot be verified. (we should not rely on using kernel
> >> modules key)
> >> Thus keys on the protected initramfs may not be required to be signed..
> > In the builtin initramfs case, the public key is included in the signed
> > image. Where is the key stored that verifies the separately signed
> > initramfs? Is there a signature chain of trust?
>
> In prototype implementation I used kernel module verification
> function... module key...
This implies that you rebuilt the kernel. :) In that case, add your
local-ca public key to the root build tree. All .x509 suffixed files
are included in the image and loaded on the system keyring.
> >
> > If there is a signature chain of trust and a local-ca signed the
> > initramfs, then the local-ca key could be added to the system keyring
> > and used to sign keys for the IMA keyring.
> >
> > thanks,
>
> You need to embed local-ca somehow into the kernel..
> Or pass/read and verify it somehow...
Exactly.
Mimi
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