Re: Linux Firmware Signing

["Luis R. Rodriguez" <mcgrof@suse.com>]

On Thu, Sep 03, 2015 at 02:14:18PM -0700, Kees Cook wrote:
> [removed bounced email addresses]
> 
> On Wed, Sep 2, 2015 at 2:37 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> > On Wed, Sep 02, 2015 at 01:54:43PM -0700, Kees Cook wrote:
> >> On Wed, Sep 2, 2015 at 11:46 AM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> >> > On Tue, Sep 01, 2015 at 11:35:05PM -0400, Mimi Zohar wrote:
> >> >> > OK great, I think that instead of passing the actual routine name we should
> >> >> > instead pass an enum type for to the LSM, that'd be easier to parse and we'd
> >> >> > then have each case well documented. Each LSM then could add its own
> >> >> > documetnation for this and can switch on it. If we went with a name we'd have
> >> >> > to to use something like __func__ and then parse that, its not clear if we need
> >> >> > to get that specific.
> >> >>
> >> >> Agreed.  IMA already defines an enumeration.
> >> >>
> >> >> /* IMA policy related functions */
> >> >> enum ima_hooks { FILE_CHECK = 1, MMAP_CHECK, BPRM_CHECK, MODULE_CHECK,
> >> >>                  FIRMWARE_CHECK, POLICY_CHECK, POST_SETATTR };
> >> >>
> >> >
> >> > We want something that is not only useful for IMA but any other LSM,
> >> > and FILE_CHECK seems very broad, not sure what BPRM_CHECK is even upon
> >> > inspecting kernel code. Likewise for POST_SETATTR. POLICY_CHECK might
> >> > be broad, perhaps its best we define then a generic set of enums to
> >> > which IMA can map them to then and let it decide. This would ensure
> >> > that the kernel defines each use caes for file inspection carefully,
> >> > documents and defines them and if an LSM wants to bunch a set together
> >> > it can do so easily with a switch statement to map set of generic
> >> > file checks in kernel to a group it already handles.
> >> >
> >> > For instance at least in the short term we'd try to unify:
> >> >
> >> > security_kernel_fw_from_file()
> >> > security_kernel_module_from_file()
> >> >
> >> > to perhaps:
> >> >
> >> > security_kernel_from_file()
> >> >
> >> > As far, as far as I can tell, the only ones we'd be ready to start
> >> > grouping immediately or with small amount of work rather soon:
> >> >
> >> > /**
> >> >  *
> >> >  * enum security_filecheck - known kernel security file checks types
> >> >  *
> >> >  * @__SECURITY_FILECHECK_UNSPEC: attribute 0 reserved
> >> >  * @SECURITY_FILECHECK_MODULE: the file being processed is a Linux kernel module
> >> >  * @SECURITY_FILECHECK_SYSDATA: the file being processed is either a firmware
> >> >  *      file or a system data file read from /lib/firmware/* by firmware_class
> >>
> >> I'd prefer a distinct category for firmware, as it carries an
> >> implication that it is an executable blob of some sort (I know not all
> >> are, though).
> >
> > The ship has sailed in terms of folks using frimrware API for things
> > that are not-firmware per se. The first one I am aware of was the
> > EEPROM override for the p54 driver. The other similar one was CPU
> > microcode, but that's a bit more close to home with "firmware". We
> > could ask users on the new system data request API I am building
> > to describe the type of file being used, as I agree differentiating
> > this for security purposes might be important. So other than just
> > file type we could have sub type category, then we could have,
> >
> > SECURITY_FILECHECK_SYSDATA, and then:
> 
> I object to executable code being called data. :)
> 
> > SECURITY_FILE_SYSDATA_FW
> > SECURITY_FILE_SYSDATA_MICROCODE
> > SECURITY_FILE_SYSDATA_EEPROM
> > SECURITY_FILE_SYSDATA_POLICY (for 802.11 regulatory I suppose)
> 
> The exception to the firmware loading is data, so the primary name
> should be firmware. Regardless, if we want distinct objects, just name
> them:
> 
> SECURITY_FILE_FIRMWARE
> SECURITY_FILE_SYSDATA
> 
> Do we need finer-grain sub types?

These two work for me.

 Luis