Re: [PATCH] wireless: fixup genregdb.awk for remove of antenna gain from wireless-regdb

Re: [PATCH] wireless: fixup genregdb.awk for remove of antenna gain from wireless-regdb

[Luis R. Rodriguez]

On Wed, Jul 2, 2014 at 7:30 AM, John W. Linville <linville@tuxdriver.com> wrote:
> On Wed, Jul 02, 2014 at 02:19:36AM +0200, Luis R. Rodriguez wrote:
>> On Tue, Jul 01, 2014 at 04:17:54PM -0400, John W. Linville wrote:
>> > Since "wireless-regdb: remove antenna gain" was merged in the
>> > wireless-regdb tree, this script has been incompatible with the
>> > 'official' regulatory database.  Let's fix it up.
>> >
>> > Signed-off-by: John W. Linville <linville@tuxdriver.com>
>> > ---
>> > I think the dfs_cac stuff is still broken, since it does not account
>> > for the starting offset of the flags.
>>
>> Indeed, but that also breaks other stuff too, because the DFS CAC stuff
>> is optional it means the flags can now start at different locations, it
>> also means that we need to distinguish a flag from a CAC.
>>
>> Here's a complex example we should test for as an example now:
>>
>> country US: DFS-FCC
>>       (2400 - 2450 @ 40), (100 mW)
>>       (2450 - 2500 @ 0), (100 mW), DFS, AUTO-BW
>>       (5170 - 5250 @ 80), (100 mW), DFS, AUTO-BW, NO-OUTDOOR
>>       (5250 - 5330 @ 0), (20), (60000), DFS, AUTO-BW
>>       (5735 - 5835 @ 80), (30)
>>       (57240 - 63720 @ 2160), (40)
>>
>> The changes below seem to address it. I think awk is too fragile to
>
> Your patch looks almost exactly like what I was thinkg to do.

OK I'll resend and update the Kconfig entry to ensure folks are aware
of the issues discussed and our resolution on requiring folks deal
with issue on the awk parser.

>> scale well and keep us sane. A C parser exists but right now it
>> ignores the DFS CAC. Having a parser is nice as it allows us to
>> modify the db.txt on the fly, however parser still requires a bit
>> of an update in code. If we wanted to avoid the parser all together
>> we could just merge a CRDA reader at build time and require a
>> a regulatory.bin file for reading instead of the db.txt. If we
>> had support for that then its really only one step further from
>> having full CRDA functionality upstream on the kernel, ie letting
>> us read the file at run time rather than just build time. If we
>> are to follow the steps from udev with its firmware loader helper
>> we might as well merge CRDA upstream, in fact we could just use
>> request_firmware_direct() for the reader, what remains questionable
>> to me is the signing stuff, but if we already have support module
>> signing checks it doesn't seem far fetched to be able to have
>> request firmware verify a signature on a file, which probably
>> ain't such a bad idea anyway. If we did this we'd have two options:
>>
>> 1) regulatory.bin reader at build time to build the static regulatory domains
>> 2) the same reader code can use request the file at run time via
>>    request_firmware_direct() and if we added signature verification
>>    it can replace CRDA
>>
>> We'd eliminate the ASCII representation completely from the build picture
>> and peg a regulatory.bin firmware to each kernel then. Thoughts?
>
> I'll have to digest this -- needs some more discussion, for sure.

Some more on this. I stumbled upon Takashi Iwai's November 2012
firmware_class Takashi Iwai's signature check series [0] [1]. His
second iteration didn't get merged but there weren't any particular
NACKs on the threads -- upon following up with him it would seem the
way to move this forward though is to integrate this somehow with Kees
Cook's work on LSM. I have yet to do that but at least by looking at
Takashi's patches it would seem moving CRDA functionality upstream is
certainly doable, this would remove both the requirement of CRDA on
userspace and remove any requirement for any build-time parsers on the
kernel. The regulatory format then would move along with the kernel.

The way I'd envision this is we'd enable drivers to pass a
specification of requirements for the firmware, one of which could be
the digital signature check. Another option would be whether or not
the firmware is required or not -- right now we use two different APIs
for this: request_firmware() and request_firmware_direct(), having a
specification could let us unify this into one a bit more cleanly. The
digital signature options then simply become an option for drivers,
and if some distributions do want to force require digital signatures
for all request_firmware() requests it can do so as well through a
Kconfig option.

[0] https://lkml.org/lkml/2012/11/5/467
[1] https://lkml.org/lkml/2012/11/8/343

  Luis

Re: [PATCH] wireless: fixup genregdb.awk for remove of antenna gain from wireless-regdb

[Kees Cook]

On Mon, Jul 14, 2014 at 2:08 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> On Wed, Jul 2, 2014 at 7:30 AM, John W. Linville <linville@tuxdriver.com> wrote:
>> On Wed, Jul 02, 2014 at 02:19:36AM +0200, Luis R. Rodriguez wrote:
>>> On Tue, Jul 01, 2014 at 04:17:54PM -0400, John W. Linville wrote:
>>> > Since "wireless-regdb: remove antenna gain" was merged in the
>>> > wireless-regdb tree, this script has been incompatible with the
>>> > 'official' regulatory database.  Let's fix it up.
>>> >
>>> > Signed-off-by: John W. Linville <linville@tuxdriver.com>
>>> > ---
>>> > I think the dfs_cac stuff is still broken, since it does not account
>>> > for the starting offset of the flags.
>>>
>>> Indeed, but that also breaks other stuff too, because the DFS CAC stuff
>>> is optional it means the flags can now start at different locations, it
>>> also means that we need to distinguish a flag from a CAC.
>>>
>>> Here's a complex example we should test for as an example now:
>>>
>>> country US: DFS-FCC
>>>       (2400 - 2450 @ 40), (100 mW)
>>>       (2450 - 2500 @ 0), (100 mW), DFS, AUTO-BW
>>>       (5170 - 5250 @ 80), (100 mW), DFS, AUTO-BW, NO-OUTDOOR
>>>       (5250 - 5330 @ 0), (20), (60000), DFS, AUTO-BW
>>>       (5735 - 5835 @ 80), (30)
>>>       (57240 - 63720 @ 2160), (40)
>>>
>>> The changes below seem to address it. I think awk is too fragile to
>>
>> Your patch looks almost exactly like what I was thinkg to do.
>
> OK I'll resend and update the Kconfig entry to ensure folks are aware
> of the issues discussed and our resolution on requiring folks deal
> with issue on the awk parser.
>
>>> scale well and keep us sane. A C parser exists but right now it
>>> ignores the DFS CAC. Having a parser is nice as it allows us to
>>> modify the db.txt on the fly, however parser still requires a bit
>>> of an update in code. If we wanted to avoid the parser all together
>>> we could just merge a CRDA reader at build time and require a
>>> a regulatory.bin file for reading instead of the db.txt. If we
>>> had support for that then its really only one step further from
>>> having full CRDA functionality upstream on the kernel, ie letting
>>> us read the file at run time rather than just build time. If we
>>> are to follow the steps from udev with its firmware loader helper
>>> we might as well merge CRDA upstream, in fact we could just use
>>> request_firmware_direct() for the reader, what remains questionable
>>> to me is the signing stuff, but if we already have support module
>>> signing checks it doesn't seem far fetched to be able to have
>>> request firmware verify a signature on a file, which probably
>>> ain't such a bad idea anyway. If we did this we'd have two options:
>>>
>>> 1) regulatory.bin reader at build time to build the static regulatory domains
>>> 2) the same reader code can use request the file at run time via
>>>    request_firmware_direct() and if we added signature verification
>>>    it can replace CRDA
>>>
>>> We'd eliminate the ASCII representation completely from the build picture
>>> and peg a regulatory.bin firmware to each kernel then. Thoughts?
>>
>> I'll have to digest this -- needs some more discussion, for sure.
>
> Some more on this. I stumbled upon Takashi Iwai's November 2012
> firmware_class Takashi Iwai's signature check series [0] [1]. His
> second iteration didn't get merged but there weren't any particular
> NACKs on the threads -- upon following up with him it would seem the
> way to move this forward though is to integrate this somehow with Kees
> Cook's work on LSM. I have yet to do that but at least by looking at

I've got LSM hooks built to check incoming firmware. It should be
trivial to add signature checks to that. For Chrome OS, that would be
redundant since we use dm-verity to check file contents. All Chrome OS
needs to know is where the firmware came from. Here's the current
tree:

https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=fw-restrict

> Takashi's patches it would seem moving CRDA functionality upstream is
> certainly doable, this would remove both the requirement of CRDA on
> userspace and remove any requirement for any build-time parsers on the
> kernel. The regulatory format then would move along with the kernel.
>
> The way I'd envision this is we'd enable drivers to pass a
> specification of requirements for the firmware, one of which could be
> the digital signature check. Another option would be whether or not
> the firmware is required or not -- right now we use two different APIs
> for this: request_firmware() and request_firmware_direct(), having a
> specification could let us unify this into one a bit more cleanly. The
> digital signature options then simply become an option for drivers,
> and if some distributions do want to force require digital signatures
> for all request_firmware() requests it can do so as well through a
> Kconfig option.
>
> [0] https://lkml.org/lkml/2012/11/5/467
> [1] https://lkml.org/lkml/2012/11/8/343
>
>   Luis

-Kees

-- 
Kees Cook
Chrome OS Security

Re: [PATCH] wireless: fixup genregdb.awk for remove of antenna gain from wireless-regdb

[Luis R. Rodriguez]

On Mon, Jul 14, 2014 at 2:13 PM, Kees Cook <keescook@chromium.org> wrote:
> On Mon, Jul 14, 2014 at 2:08 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
>> On Wed, Jul 2, 2014 at 7:30 AM, John W. Linville <linville@tuxdriver.com> wrote:
>>> On Wed, Jul 02, 2014 at 02:19:36AM +0200, Luis R. Rodriguez wrote:
>>>> On Tue, Jul 01, 2014 at 04:17:54PM -0400, John W. Linville wrote:
>>>> > Since "wireless-regdb: remove antenna gain" was merged in the
>>>> > wireless-regdb tree, this script has been incompatible with the
>>>> > 'official' regulatory database.  Let's fix it up.
>>>> >
>>>> > Signed-off-by: John W. Linville <linville@tuxdriver.com>
>>>> > ---
>>>> > I think the dfs_cac stuff is still broken, since it does not account
>>>> > for the starting offset of the flags.
>>>>
>>>> Indeed, but that also breaks other stuff too, because the DFS CAC stuff
>>>> is optional it means the flags can now start at different locations, it
>>>> also means that we need to distinguish a flag from a CAC.
>>>>
>>>> Here's a complex example we should test for as an example now:
>>>>
>>>> country US: DFS-FCC
>>>>       (2400 - 2450 @ 40), (100 mW)
>>>>       (2450 - 2500 @ 0), (100 mW), DFS, AUTO-BW
>>>>       (5170 - 5250 @ 80), (100 mW), DFS, AUTO-BW, NO-OUTDOOR
>>>>       (5250 - 5330 @ 0), (20), (60000), DFS, AUTO-BW
>>>>       (5735 - 5835 @ 80), (30)
>>>>       (57240 - 63720 @ 2160), (40)
>>>>
>>>> The changes below seem to address it. I think awk is too fragile to
>>>
>>> Your patch looks almost exactly like what I was thinkg to do.
>>
>> OK I'll resend and update the Kconfig entry to ensure folks are aware
>> of the issues discussed and our resolution on requiring folks deal
>> with issue on the awk parser.
>>
>>>> scale well and keep us sane. A C parser exists but right now it
>>>> ignores the DFS CAC. Having a parser is nice as it allows us to
>>>> modify the db.txt on the fly, however parser still requires a bit
>>>> of an update in code. If we wanted to avoid the parser all together
>>>> we could just merge a CRDA reader at build time and require a
>>>> a regulatory.bin file for reading instead of the db.txt. If we
>>>> had support for that then its really only one step further from
>>>> having full CRDA functionality upstream on the kernel, ie letting
>>>> us read the file at run time rather than just build time. If we
>>>> are to follow the steps from udev with its firmware loader helper
>>>> we might as well merge CRDA upstream, in fact we could just use
>>>> request_firmware_direct() for the reader, what remains questionable
>>>> to me is the signing stuff, but if we already have support module
>>>> signing checks it doesn't seem far fetched to be able to have
>>>> request firmware verify a signature on a file, which probably
>>>> ain't such a bad idea anyway. If we did this we'd have two options:
>>>>
>>>> 1) regulatory.bin reader at build time to build the static regulatory domains
>>>> 2) the same reader code can use request the file at run time via
>>>>    request_firmware_direct() and if we added signature verification
>>>>    it can replace CRDA
>>>>
>>>> We'd eliminate the ASCII representation completely from the build picture
>>>> and peg a regulatory.bin firmware to each kernel then. Thoughts?
>>>
>>> I'll have to digest this -- needs some more discussion, for sure.
>>
>> Some more on this. I stumbled upon Takashi Iwai's November 2012
>> firmware_class Takashi Iwai's signature check series [0] [1]. His
>> second iteration didn't get merged but there weren't any particular
>> NACKs on the threads -- upon following up with him it would seem the
>> way to move this forward though is to integrate this somehow with Kees
>> Cook's work on LSM. I have yet to do that but at least by looking at
>
> I've got LSM hooks built to check incoming firmware. It should be
> trivial to add signature checks to that. For Chrome OS, that would be
> redundant since we use dm-verity to check file contents. All Chrome OS
> needs to know is where the firmware came from. Here's the current
> tree:
>
> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=fw-restrict

Awesome! Base do a quick glance it seems Android also uses this,
dm-verity [0] uses public keys as well so it would indeed also provide
authenticity / integrity checks which would indeed make firmware
signature checks redundant, the only requirement however is you'd
require the checks on the partition, and I do suspect not all
distributions will want to go down this path. If we can extend the LSM
hooks to give the option for signatures on firmware we'd enable
distributions to pick and choose a strategy. Can we let LSM hooks then
figure out if a digital signature is superfluous if dm-verity is being
used ? I suspect there may be some cases where a module / part of the
kernel may want to *force* the presence of a signature check but I
don't think that this is a requirement for all use cases.

[0] https://source.android.com/devices/tech/security/dm-verity.html

  Luis

Re: [PATCH] wireless: fixup genregdb.awk for remove of antenna gain from wireless-regdb

[Kees Cook]

On Mon, Jul 14, 2014 at 2:33 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> On Mon, Jul 14, 2014 at 2:13 PM, Kees Cook <keescook@chromium.org> wrote:
>> On Mon, Jul 14, 2014 at 2:08 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
>>> On Wed, Jul 2, 2014 at 7:30 AM, John W. Linville <linville@tuxdriver.com> wrote:
>>>> On Wed, Jul 02, 2014 at 02:19:36AM +0200, Luis R. Rodriguez wrote:
>>>>> On Tue, Jul 01, 2014 at 04:17:54PM -0400, John W. Linville wrote:
>>>>> > Since "wireless-regdb: remove antenna gain" was merged in the
>>>>> > wireless-regdb tree, this script has been incompatible with the
>>>>> > 'official' regulatory database.  Let's fix it up.
>>>>> >
>>>>> > Signed-off-by: John W. Linville <linville@tuxdriver.com>
>>>>> > ---
>>>>> > I think the dfs_cac stuff is still broken, since it does not account
>>>>> > for the starting offset of the flags.
>>>>>
>>>>> Indeed, but that also breaks other stuff too, because the DFS CAC stuff
>>>>> is optional it means the flags can now start at different locations, it
>>>>> also means that we need to distinguish a flag from a CAC.
>>>>>
>>>>> Here's a complex example we should test for as an example now:
>>>>>
>>>>> country US: DFS-FCC
>>>>>       (2400 - 2450 @ 40), (100 mW)
>>>>>       (2450 - 2500 @ 0), (100 mW), DFS, AUTO-BW
>>>>>       (5170 - 5250 @ 80), (100 mW), DFS, AUTO-BW, NO-OUTDOOR
>>>>>       (5250 - 5330 @ 0), (20), (60000), DFS, AUTO-BW
>>>>>       (5735 - 5835 @ 80), (30)
>>>>>       (57240 - 63720 @ 2160), (40)
>>>>>
>>>>> The changes below seem to address it. I think awk is too fragile to
>>>>
>>>> Your patch looks almost exactly like what I was thinkg to do.
>>>
>>> OK I'll resend and update the Kconfig entry to ensure folks are aware
>>> of the issues discussed and our resolution on requiring folks deal
>>> with issue on the awk parser.
>>>
>>>>> scale well and keep us sane. A C parser exists but right now it
>>>>> ignores the DFS CAC. Having a parser is nice as it allows us to
>>>>> modify the db.txt on the fly, however parser still requires a bit
>>>>> of an update in code. If we wanted to avoid the parser all together
>>>>> we could just merge a CRDA reader at build time and require a
>>>>> a regulatory.bin file for reading instead of the db.txt. If we
>>>>> had support for that then its really only one step further from
>>>>> having full CRDA functionality upstream on the kernel, ie letting
>>>>> us read the file at run time rather than just build time. If we
>>>>> are to follow the steps from udev with its firmware loader helper
>>>>> we might as well merge CRDA upstream, in fact we could just use
>>>>> request_firmware_direct() for the reader, what remains questionable
>>>>> to me is the signing stuff, but if we already have support module
>>>>> signing checks it doesn't seem far fetched to be able to have
>>>>> request firmware verify a signature on a file, which probably
>>>>> ain't such a bad idea anyway. If we did this we'd have two options:
>>>>>
>>>>> 1) regulatory.bin reader at build time to build the static regulatory domains
>>>>> 2) the same reader code can use request the file at run time via
>>>>>    request_firmware_direct() and if we added signature verification
>>>>>    it can replace CRDA
>>>>>
>>>>> We'd eliminate the ASCII representation completely from the build picture
>>>>> and peg a regulatory.bin firmware to each kernel then. Thoughts?
>>>>
>>>> I'll have to digest this -- needs some more discussion, for sure.
>>>
>>> Some more on this. I stumbled upon Takashi Iwai's November 2012
>>> firmware_class Takashi Iwai's signature check series [0] [1]. His
>>> second iteration didn't get merged but there weren't any particular
>>> NACKs on the threads -- upon following up with him it would seem the
>>> way to move this forward though is to integrate this somehow with Kees
>>> Cook's work on LSM. I have yet to do that but at least by looking at
>>
>> I've got LSM hooks built to check incoming firmware. It should be
>> trivial to add signature checks to that. For Chrome OS, that would be
>> redundant since we use dm-verity to check file contents. All Chrome OS
>> needs to know is where the firmware came from. Here's the current
>> tree:
>>
>> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=fw-restrict
>
> Awesome! Base do a quick glance it seems Android also uses this,
> dm-verity [0] uses public keys as well so it would indeed also provide
> authenticity / integrity checks which would indeed make firmware
> signature checks redundant, the only requirement however is you'd
> require the checks on the partition, and I do suspect not all
> distributions will want to go down this path. If we can extend the LSM
> hooks to give the option for signatures on firmware we'd enable
> distributions to pick and choose a strategy. Can we let LSM hooks then
> figure out if a digital signature is superfluous if dm-verity is being
> used ? I suspect there may be some cases where a module / part of the
> kernel may want to *force* the presence of a signature check but I
> don't think that this is a requirement for all use cases.

I'm not sure what the best approach is for this. I added the
finit_module syscall to provide a similar interface for kernel module
loading, but the module signing happens in a separate path. I think
it'd be nice to move things around a little on the module signing path
so it was all exposed via LSM, and then install a sig-checking LSM.
(Which may or may not also require stacked LSMs, a project that is
being worked on as well.)

Note also that we may need something like this for kexec too.

I will send out the fw validation series now...

-Kees

>
> [0] https://source.android.com/devices/tech/security/dm-verity.html
>
>   Luis



-- 
Kees Cook
Chrome OS Security

Re: [PATCH] wireless: fixup genregdb.awk for remove of antenna gain from wireless-regdb

[Luis R. Rodriguez]

On Mon, Jul 14, 2014 at 02:37:50PM -0700, Kees Cook wrote:
> On Mon, Jul 14, 2014 at 2:33 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> > On Mon, Jul 14, 2014 at 2:13 PM, Kees Cook <keescook@chromium.org> wrote:
> >> On Mon, Jul 14, 2014 at 2:08 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> >>> On Wed, Jul 2, 2014 at 7:30 AM, John W. Linville <linville@tuxdriver.com> wrote:
> >>>> On Wed, Jul 02, 2014 at 02:19:36AM +0200, Luis R. Rodriguez wrote:
> >>>>> On Tue, Jul 01, 2014 at 04:17:54PM -0400, John W. Linville wrote:
> >>>>> > Since "wireless-regdb: remove antenna gain" was merged in the
> >>>>> > wireless-regdb tree, this script has been incompatible with the
> >>>>> > 'official' regulatory database.  Let's fix it up.
> >>>>> >
> >>>>> > Signed-off-by: John W. Linville <linville@tuxdriver.com>
> >>>>> > ---
> >>>>> > I think the dfs_cac stuff is still broken, since it does not account
> >>>>> > for the starting offset of the flags.
> >>>>>
> >>>>> Indeed, but that also breaks other stuff too, because the DFS CAC stuff
> >>>>> is optional it means the flags can now start at different locations, it
> >>>>> also means that we need to distinguish a flag from a CAC.
> >>>>>
> >>>>> Here's a complex example we should test for as an example now:
> >>>>>
> >>>>> country US: DFS-FCC
> >>>>>       (2400 - 2450 @ 40), (100 mW)
> >>>>>       (2450 - 2500 @ 0), (100 mW), DFS, AUTO-BW
> >>>>>       (5170 - 5250 @ 80), (100 mW), DFS, AUTO-BW, NO-OUTDOOR
> >>>>>       (5250 - 5330 @ 0), (20), (60000), DFS, AUTO-BW
> >>>>>       (5735 - 5835 @ 80), (30)
> >>>>>       (57240 - 63720 @ 2160), (40)
> >>>>>
> >>>>> The changes below seem to address it. I think awk is too fragile to
> >>>>
> >>>> Your patch looks almost exactly like what I was thinkg to do.
> >>>
> >>> OK I'll resend and update the Kconfig entry to ensure folks are aware
> >>> of the issues discussed and our resolution on requiring folks deal
> >>> with issue on the awk parser.
> >>>
> >>>>> scale well and keep us sane. A C parser exists but right now it
> >>>>> ignores the DFS CAC. Having a parser is nice as it allows us to
> >>>>> modify the db.txt on the fly, however parser still requires a bit
> >>>>> of an update in code. If we wanted to avoid the parser all together
> >>>>> we could just merge a CRDA reader at build time and require a
> >>>>> a regulatory.bin file for reading instead of the db.txt. If we
> >>>>> had support for that then its really only one step further from
> >>>>> having full CRDA functionality upstream on the kernel, ie letting
> >>>>> us read the file at run time rather than just build time. If we
> >>>>> are to follow the steps from udev with its firmware loader helper
> >>>>> we might as well merge CRDA upstream, in fact we could just use
> >>>>> request_firmware_direct() for the reader, what remains questionable
> >>>>> to me is the signing stuff, but if we already have support module
> >>>>> signing checks it doesn't seem far fetched to be able to have
> >>>>> request firmware verify a signature on a file, which probably
> >>>>> ain't such a bad idea anyway. If we did this we'd have two options:
> >>>>>
> >>>>> 1) regulatory.bin reader at build time to build the static regulatory domains
> >>>>> 2) the same reader code can use request the file at run time via
> >>>>>    request_firmware_direct() and if we added signature verification
> >>>>>    it can replace CRDA
> >>>>>
> >>>>> We'd eliminate the ASCII representation completely from the build picture
> >>>>> and peg a regulatory.bin firmware to each kernel then. Thoughts?
> >>>>
> >>>> I'll have to digest this -- needs some more discussion, for sure.
> >>>
> >>> Some more on this. I stumbled upon Takashi Iwai's November 2012
> >>> firmware_class Takashi Iwai's signature check series [0] [1]. His
> >>> second iteration didn't get merged but there weren't any particular
> >>> NACKs on the threads -- upon following up with him it would seem the
> >>> way to move this forward though is to integrate this somehow with Kees
> >>> Cook's work on LSM. I have yet to do that but at least by looking at
> >>
> >> I've got LSM hooks built to check incoming firmware. It should be
> >> trivial to add signature checks to that. For Chrome OS, that would be
> >> redundant since we use dm-verity to check file contents. All Chrome OS
> >> needs to know is where the firmware came from. Here's the current
> >> tree:
> >>
> >> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=fw-restrict
> >
> > Awesome! Base do a quick glance it seems Android also uses this,
> > dm-verity [0] uses public keys as well so it would indeed also provide
> > authenticity / integrity checks which would indeed make firmware
> > signature checks redundant, the only requirement however is you'd
> > require the checks on the partition, and I do suspect not all
> > distributions will want to go down this path. If we can extend the LSM
> > hooks to give the option for signatures on firmware we'd enable
> > distributions to pick and choose a strategy. Can we let LSM hooks then
> > figure out if a digital signature is superfluous if dm-verity is being
> > used ? I suspect there may be some cases where a module / part of the
> > kernel may want to *force* the presence of a signature check but I
> > don't think that this is a requirement for all use cases.
> 
> I'm not sure what the best approach is for this. I added the
> finit_module syscall to provide a similar interface for kernel module
> loading, but the module signing happens in a separate path.

Yeah that is all module specific and I think it'd be overkill to add
something fw specific, even though we could share the same file descriptor
approach. Wonder if a more general kobject thing could be a good way
to scale this without having to add any more syscalls for the different
use cases.

> I think
> it'd be nice to move things around a little on the module signing path
> so it was all exposed via LSM, and then install a sig-checking LSM.
> (Which may or may not also require stacked LSMs, a project that is
> being worked on as well.)
> 
> Note also that we may need something like this for kexec too.

Makes sense.

  Luis