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From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Matthew Garrett <mjg59@google.com>,
	Mimi Zohar <zohar@linux.vnet.ibm.com>,
	David Howells <dhowells@redhat.com>,
	Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	"AKASHI, Takahiro" <takahiro.akashi@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jan Blunck <jblunck@infradead.org>,
	Julia Lawall <julia.lawall@lip6.fr>,
	Marcus Meissner <meissner@suse.de>, Gary Lin <GLin@suse.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel lockdown
Date: Fri, 8 Dec 2017 00:02:38 +0100
Message-ID: <20171207230238.GW729@wotan.suse.de> (raw)
In-Reply-To: <20171205102757.GA12982@amd>

On Tue, Dec 05, 2017 at 11:27:58AM +0100, Pavel Machek wrote:
> Hi!
> 
> > > Our ability to determine that userland hasn't been tampered with
> > > depends on the kernel being trustworthy. If userland can upload
> > > arbitrary firmware to DMA-capable devices then we can no longer trust
> > > the kernel. So yes, firmware is special.
> > 
> > You're ignoring the whole "firmware is already signed by the hardware
> > manufacturer and we don't even have access to it" part.
> 
> Well... I guess we'd prefer the firmware _not_ be signed, so we can
> fix security holes in that after the vendor lost interest... Bugs in
> the wifi stacks seemed patcheable that way.
> 
> There is GPLed firmware available for some USB wifi's. We really
> should make sure firmware signing is not mandatory/encouraged for the hw vendors.

I share this concern and interest, specially as more device drivers get purposely
stupid and most of the technology and fun things shift to firmware. Its precisely
for this same reason why most manufacturers won't be opening up more firmware, as
they could argue tons of value-add is in firmware now.

One has to be realistic though, as one of the few folks who pushed to open
source (and GPL) a few of the open source firmwares we have for WiFi, I realize
we have no option but to accept the fate that most manufacturers *will*
use and require signed firmware in the future.

If you're concerned about this you have only a few options.

One is to get more and more folks reverse engineer firmware. This won't help
if you can't deploy unsigned firmware though. But you have to also look at it
from a practical point of view, in order to do development you *have* to have
some sort of knobs to turn off fw signing verification, so it should be a
matter of looking hard. And for devices where this is not obvious or almost
impossible, hope for an exploit.

Another option is to argue for the engineering gain for having open firmware,
and a viable sensible and responsible option to continue to do R&D and innovation
with open firmware. We did this with WiFi long ago, see CFG80211_CERTIFICATION_ONUS
and the slew of open firmware released. The fact that we have open firmware
repositories and also a respective proprietary firmwares for the same device
could be used to metrically show the gains that such development had over time,
in a quantifiable form (features, bug fixes, security issues fixed). There's
tons of data available which could enable a researcher to have a field with
this.

And the last option is to just argue for a sensible opt-out knob to be documented
as part of our rights or due to general long term community security interests.
Just as with UEFI one can say one does not trust any key present already on the
platform, one should also be able to do the same for peripheral devices and their
own corresponding firmware -- a knob to disable firmware signing.

Sadly *all* of these are lofty pie in the sky objectives.

What the likely outcome will be is we sit and wait for the worst of the possible
security shit issues to hit the fan for the large IoT universe, and then hope
we can use this as leverage to require documenting such opt-out knobs just as
with UEFI's opt-out mechanism.

Although one would expect that such exploits already have happened, in practice
not at the interface we're talking about here, which is for /lib/firmware/.
For instance the Intel Management Engine does not use this interface, and
neither do some of the storage driver and arrays I've been bluntly told have
had tons of backdoors for years. Its precisely because of this lack of known
issues with security for /lib/firmware exploits that I'm willing to put signing
of /lib/firmware on the side for now.

We just haven't had many known attacks come in through here.

  Luis

  reply index

Thread overview: 151+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-19 14:50 David Howells
2017-10-19 14:50 ` [PATCH 01/27] Add the ability to lock down access to the running kernel image David Howells
2017-10-20 23:19   ` James Morris
2017-10-19 14:50 ` [PATCH 02/27] Add a SysRq option to lift kernel lockdown David Howells
2017-10-19 17:20   ` Randy Dunlap
2017-10-19 22:12   ` David Howells
2017-11-07 17:39   ` Thiago Jung Bauermann
2017-11-07 22:56   ` David Howells
2017-10-19 14:50 ` [PATCH 03/27] Enforce module signatures if the kernel is locked down David Howells
2017-10-20  6:33   ` joeyli
2017-10-20 23:21   ` James Morris
2017-10-27 18:48   ` Mimi Zohar
2017-10-30 17:00   ` David Howells
2017-10-30 17:52     ` Mimi Zohar
2017-11-02 17:22   ` David Howells
2017-11-02 19:13     ` Mimi Zohar
2017-11-02 21:30     ` David Howells
2017-11-02 21:41       ` Mimi Zohar
2017-11-02 22:01       ` David Howells
2017-11-02 22:18         ` Mimi Zohar
2017-10-19 14:51 ` [PATCH 04/27] Restrict /dev/mem and /dev/kmem when " David Howells
2017-10-20  6:37   ` joeyli
2017-10-20 23:21   ` James Morris
2017-10-19 14:51 ` [PATCH 05/27] kexec: Disable at runtime if " David Howells
2017-10-20  6:38   ` joeyli
2017-10-20 23:22   ` James Morris
2017-10-19 14:51 ` [PATCH 06/27] Copy secure_boot flag in boot params across kexec reboot David Howells
2017-10-20  6:40   ` joeyli
2017-10-19 14:51 ` [PATCH 07/27] kexec_file: Disable at runtime if securelevel has been set David Howells
2017-10-20 23:26   ` James Morris
2017-10-23 15:54   ` Mimi Zohar
2017-10-26  7:42     ` joeyli
2017-10-26 14:17       ` Mimi Zohar
2017-10-27 19:30         ` Mimi Zohar
2017-10-27 19:32         ` Mimi Zohar
2017-10-28  8:34           ` joeyli
2017-10-29 22:26             ` Mimi Zohar
2017-10-30  9:00       ` David Howells
2017-10-30 12:01         ` Mimi Zohar
2017-10-26 15:02     ` David Howells
2017-10-26 15:46       ` Mimi Zohar
2017-10-30 15:49       ` David Howells
2017-10-30 16:43         ` Mimi Zohar
2017-11-02 17:00         ` David Howells
2017-10-26 14:51   ` David Howells
2017-11-02 17:29   ` David Howells
2017-10-19 14:51 ` [PATCH 08/27] hibernate: Disable when the kernel is locked down David Howells
2017-10-20  6:40   ` joeyli
2017-10-19 14:51 ` [PATCH 09/27] uswsusp: " David Howells
2017-10-20  6:41   ` joeyli
2017-10-20 23:29   ` James Morris
2017-10-19 14:51 ` [PATCH 10/27] PCI: Lock down BAR access " David Howells
2017-10-20  6:42   ` joeyli
2017-10-19 14:51 ` [PATCH 11/27] x86: Lock down IO port " David Howells
2017-10-20  6:43   ` joeyli
2017-10-19 14:52 ` [PATCH 12/27] x86/msr: Restrict MSR " David Howells
2017-10-20  6:43   ` joeyli
2017-10-20 18:09   ` Alan Cox
2017-10-20 20:48   ` David Howells
2017-10-21  4:39     ` joeyli
2017-10-23 14:49   ` David Howells
2017-10-25 14:03     ` joeyli
2017-10-19 14:52 ` [PATCH 13/27] asus-wmi: Restrict debugfs interface " David Howells
2017-10-20  6:44   ` joeyli
2017-10-19 14:52 ` [PATCH 14/27] ACPI: Limit access to custom_method " David Howells
2017-10-20  6:45   ` joeyli
2017-10-19 14:52 ` [PATCH 15/27] acpi: Ignore acpi_rsdp kernel param when the kernel has been " David Howells
2017-10-20  6:45   ` joeyli
2017-10-19 14:52 ` [PATCH 16/27] acpi: Disable ACPI table override if the kernel is " David Howells
2017-10-20  6:46   ` joeyli
2017-10-19 14:52 ` [PATCH 17/27] acpi: Disable APEI error injection " David Howells
2017-10-20  6:47   ` joeyli
2017-10-19 14:52 ` [PATCH 18/27] bpf: Restrict kernel image access functions when " David Howells
2017-10-19 22:18   ` Alexei Starovoitov
2017-10-20  2:47     ` joeyli
2017-10-20  8:08     ` David Howells
2017-10-20 15:57       ` jlee
2017-10-20 23:00         ` Alexei Starovoitov
2017-10-23 14:51         ` David Howells
2017-10-20 16:03       ` David Howells
2017-10-20 16:43         ` jlee
2017-10-23 14:53         ` David Howells
2017-10-25  7:07           ` joeyli
2017-10-19 22:48   ` David Howells
2017-10-19 23:31     ` Alexei Starovoitov
2017-11-09 17:15     ` David Howells
2017-10-19 14:52 ` [PATCH 19/27] scsi: Lock down the eata driver David Howells
2017-10-19 14:53 ` [PATCH 20/27] Prohibit PCMCIA CIS storage when the kernel is locked down David Howells
2017-10-19 14:53 ` [PATCH 21/27] Lock down TIOCSSERIAL David Howells
2017-10-19 14:53 ` [PATCH 22/27] Lock down module params that specify hardware parameters (eg. ioport) David Howells
2017-10-19 14:53 ` [PATCH 23/27] x86/mmiotrace: Lock down the testmmiotrace module David Howells
2017-10-19 14:53 ` [PATCH 24/27] debugfs: Disallow use of debugfs files when the kernel is locked down David Howells
2017-10-19 14:53 ` [PATCH 25/27] Lock down /proc/kcore David Howells
2017-10-21  2:11   ` James Morris
2017-10-23 14:56   ` David Howells
2017-10-19 14:53 ` [PATCH 26/27] efi: Add an EFI_SECURE_BOOT flag to indicate secure boot mode David Howells
2017-10-21  2:19   ` James Morris
2017-10-23 14:58   ` David Howells
2017-10-19 14:53 ` [PATCH 27/27] efi: Lock down the kernel if booted in " David Howells
2017-10-19 22:39 ` [PATCH 00/27] security, efi: Add kernel lockdown David Howells
2017-10-23 14:34 ` [PATCH 04/27] Restrict /dev/mem and /dev/kmem when the kernel is locked down David Howells
2017-10-24 10:48   ` Ethan Zhao
2017-10-24 14:56   ` David Howells
2017-11-02 22:01 ` [PATCH 00/27] security, efi: Add kernel lockdown Mimi Zohar
2017-11-02 22:04 ` Firmware signing -- " David Howells
2017-11-02 22:10   ` Mimi Zohar
2017-11-07 23:07     ` Luis R. Rodriguez
2017-11-08  6:15       ` AKASHI, Takahiro
2017-11-08 19:46         ` Luis R. Rodriguez
2017-11-09  1:48           ` AKASHI, Takahiro
2017-11-09  2:17             ` Mimi Zohar
2017-11-09  4:46               ` AKASHI, Takahiro
2017-11-10 13:37                 ` Mimi Zohar
2017-11-11  2:32                 ` Alan Cox
2017-11-13 11:49                   ` Mimi Zohar
2017-11-13 17:42                   ` Luis R. Rodriguez
2017-11-13 21:08                     ` Alan Cox
2017-12-04 19:51                       ` Luis R. Rodriguez
2017-12-07 15:32                         ` Alan Cox
2017-11-13 21:44                     ` David Howells
2017-11-13 22:09                       ` Linus Torvalds
2017-11-14  0:20                         ` Alan Cox
2017-11-14 12:21                         ` Mimi Zohar
2017-11-14 12:38                           ` Greg Kroah-Hartman
2017-11-14 13:17                             ` Mimi Zohar
2017-11-14 17:34                           ` Linus Torvalds
2017-11-14 19:58                             ` Matthew Garrett
2017-11-14 20:18                               ` Linus Torvalds
2017-11-14 20:31                                 ` Matthew Garrett
2017-11-14 20:35                                   ` Linus Torvalds
2017-11-14 20:37                                     ` Matthew Garrett
2017-11-14 20:50                                 ` Luis R. Rodriguez
2017-11-14 20:55                                   ` Matthew Garrett
2017-11-14 22:14                                     ` James Bottomley
2017-11-14 22:17                                       ` Matthew Garrett
2017-11-14 22:31                                         ` James Bottomley
2017-11-14 22:34                                           ` Matthew Garrett
2017-11-15 11:49                                   ` Mimi Zohar
2017-11-15 17:52                                     ` Luis R. Rodriguez
2017-11-15 19:56                                       ` Mimi Zohar
2017-11-15 20:46                                         ` Luis R. Rodriguez
2017-11-16  0:05                                           ` Mimi Zohar
2017-12-05 10:27                                 ` Pavel Machek
2017-12-07 23:02                                   ` Luis R. Rodriguez [this message]
2017-12-08 17:11                                     ` Alan Cox
2017-11-10  1:46             ` Luis R. Rodriguez
2017-11-10 13:45               ` Mimi Zohar
2017-11-13 18:50                 ` Luis R. Rodriguez
2017-11-13 19:08                   ` Luis R. Rodriguez
2017-11-08 20:01       ` Mimi Zohar
2017-11-08 20:09         ` Luis R. Rodriguez

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