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From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Kalle Valo <kvalo@codeaurora.org>,
	Seth Forshee <seth.forshee@canonical.com>,
	Johannes Berg <johannes.berg@intel.com>
Cc: linux-integrity@vger.kernel.org,
	Hans de Goede <hdegoede@redhat.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Peter Jones <pjones@redhat.com>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, David Howells <dhowells@redhat.com>,
	Kees Cook <keescook@chromium.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andres Rodriguez <andresx7@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 3/6] firmware: differentiate between signed regulatory.db and other firmware
Date: Wed, 09 May 2018 07:30:28 -0400	[thread overview]
Message-ID: <1525865428.3551.175.camel@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180508173404.GG27853@wotan.suse.de>

On Tue, 2018-05-08 at 17:34 +0000, Luis R. Rodriguez wrote:
> On Thu, May 03, 2018 at 08:24:26PM -0400, Mimi Zohar wrote:
> > On Fri, 2018-05-04 at 00:07 +0000, Luis R. Rodriguez wrote:
> > > On Tue, May 01, 2018 at 09:48:20AM -0400, Mimi Zohar wrote:
> > > > Allow LSMs and IMA to differentiate between signed regulatory.db and
> > > > other firmware.
> > > > 
> > > > Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> > > > Cc: Luis R. Rodriguez <mcgrof@suse.com>
> > > > Cc: David Howells <dhowells@redhat.com>
> > > > Cc: Kees Cook <keescook@chromium.org>
> > > > Cc: Seth Forshee <seth.forshee@canonical.com>
> > > > Cc: Johannes Berg <johannes.berg@intel.com>
> > > > ---
> > > >  drivers/base/firmware_loader/main.c | 5 +++++
> > > >  include/linux/fs.h                  | 1 +
> > > >  2 files changed, 6 insertions(+)
> > > > 
> > > > diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
> > > > index eb34089e4299..d7cdf04a8681 100644
> > > > --- a/drivers/base/firmware_loader/main.c
> > > > +++ b/drivers/base/firmware_loader/main.c
> > > > @@ -318,6 +318,11 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv)
> > > >  			break;
> > > >  		}
> > > >  
> > > > +#ifdef CONFIG_CFG80211_REQUIRE_SIGNED_REGDB
> > > > +		if ((strcmp(fw_priv->fw_name, "regulatory.db") == 0) ||
> > > > +		    (strcmp(fw_priv->fw_name, "regulatory.db.p7s") == 0))
> > > > +			id = READING_FIRMWARE_REGULATORY_DB;
> > > > +#endif
> > > 
> > > Whoa, no way.
> > 
> > There are two methods for the kernel to verify firmware signatures.
> 
> Yes, but although CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is its own kernel
> mechanism to verify firmware it uses the request_firmware*() API for
> regulatory.db and regulatory.db.p7s, and IMA already can appraise these two
> files since the firmware API is used.

IMA-appraisal can verify a signature stored as an xattr, but not a
detached signature.  That support could be added, but isn't there
today.  Today, a regulatory.db signature would have to be stored as an
xattr. 

> 
> As such I see no reason to add a new ID for them at all.
> K
> Its not providing an *alternative*, its providing an *extra* kernel measure.
> If anything CONFIG_CFG80211_REQUIRE_SIGNED_REGDB perhaps should be its own
> stacked LSM. I'd be open to see patches which set that out. May be a
> cleaner interface.
> 
> > If both are enabled, do we require both signatures or is one enough.
> 
> Good question. Considering it as a stacked LSM (although not implemented
> as one), I'd say its up to who enabled the Kconfig entries. If IMA and
> CONFIG_CFG80211_REQUIRE_SIGNED_REGDB are enabled then both. If someone enabled
> IMA though, then surely I agree that enabling
> CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is stupid and redundant, but its up to the
> system integrator to decide.

Just because IMA-appraisal is enabled in the kernel doesn't mean that
firmware signatures will be verified.  That is a run time policy
decision.

> 
> If we however want to make it clear that such things as
> CONFIG_CFG80211_REQUIRE_SIGNED_REGDB are not required when IMA is enabled we
> could just make the kconfig depend on !IMA or something?  Or perhaps a new
> kconfig for IMA which if selected it means that drivers can opt to open code
> *further* kernel signature verification, even though IMA already is sufficient.
> Perhaps CONFIG_ENABLE_IMA_OVERLAPPING, and the driver depends on it?

The existing CONFIG_IMA_APPRAISE is not enough.  If there was a build
time IMA config that translated into an IMA policy requiring firmware
signature verification (eg. CONFIG_IMA_APPRAISE_FIRMWARE), this could
be sorted out at build time.

> 
> > Assigning a different id for regdb signed firmware allows LSMs and IMA
> > to handle regdb files differently.
> 
> That's not the main concern here, its the precedent we are setting here for
> any new kernel interface which open codes firmware signing on its own. What
> you are doing means other kernel users who open codes their own firmware
> signing may need to add yet-another reading ID. That doesn't either look
> well on code, and seems kind of silly from a coding perspective given
> the above, in which I clarify IMA still is doing its own appraisal on it.

Suppose,

1. Either CONFIG_CFG80211_REQUIRE_SIGNED_REGDB or
"CONFIG_IMA_APPRAISE_FIRMWARE" would be configured at build.

2. If CONFIG_CFG80211_REQUIRE_SIGNED_REGDB is configured, not
"CONFIG_IMA_APPRAISE_FIRMWARE", a custom IMA-policy rule that
appraises the firmware signature could be defined.  In this case, both
signature verification methods would be enforced.

then READING_FIRMWARE_REGULATORY_DB would not be needed.

Mimi

> 
> > > >  		fw_priv->size = 0;
> > > >  		rc = kernel_read_file_from_path(path, &fw_priv->data, &size,
> > > >  						msize, id);
> > > > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > > > index dc16a73c3d38..d1153c2884b9 100644
> > > > --- a/include/linux/fs.h
> > > > +++ b/include/linux/fs.h
> > > > @@ -2811,6 +2811,7 @@ extern int do_pipe_flags(int *, int);
> > > >  	id(FIRMWARE, firmware)		\
> > > >  	id(FIRMWARE_PREALLOC_BUFFER, firmware)	\
> > > >  	id(FIRMWARE_FALLBACK, firmware)	\
> > > > +	id(FIRMWARE_REGULATORY_DB, firmware)	\
> > > 
> > > Why could IMA not appriase these files? They are part of the standard path.
> > 
> > The subsequent patch attempts to verify the IMA-appraisal signature, but on
> > failure it falls back to allowing regdb signatures. 
> > For systems that only want to load firmware based on IMA-appraisal, then
> >regdb wouldn't be enabled.
> 
> I think we can codify this a bit better, without a new ID.
> 
>   Luis
> 

  reply	other threads:[~2018-05-09 11:30 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-01 13:48 [PATCH 0/6] firmware: kernel signature verification Mimi Zohar
2018-05-01 13:48 ` [PATCH 1/6] firmware: permit LSMs and IMA to fail firmware sysfs fallback loading Mimi Zohar
2018-05-04  0:02   ` Luis R. Rodriguez
2018-05-04  0:36     ` Mimi Zohar
2018-05-01 13:48 ` [PATCH 2/6] ima: prevent sysfs fallback firmware loading Mimi Zohar
2018-05-04  0:06   ` Luis R. Rodriguez
2018-05-01 13:48 ` [PATCH 3/6] firmware: differentiate between signed regulatory.db and other firmware Mimi Zohar
2018-05-04  0:07   ` Luis R. Rodriguez
2018-05-04  0:24     ` Mimi Zohar
2018-05-08 17:34       ` Luis R. Rodriguez
2018-05-09 11:30         ` Mimi Zohar [this message]
2018-05-09 19:15           ` Luis R. Rodriguez
2018-05-09 19:57             ` Mimi Zohar
2018-05-09 21:22               ` Luis R. Rodriguez
2018-05-09 22:06                 ` Mimi Zohar
2018-05-09 23:48                   ` Luis R. Rodriguez
2018-05-10  2:00                     ` Mimi Zohar
2018-05-10 23:26                       ` Luis R. Rodriguez
2018-05-11  5:00                         ` Mimi Zohar
2018-05-11 21:52                           ` Luis R. Rodriguez
2018-05-14 12:58                             ` Mimi Zohar
2018-05-14 19:28                               ` Luis R. Rodriguez
2018-05-15  2:02                                 ` Mimi Zohar
2018-05-15  3:26                                   ` Luis R. Rodriguez
2018-05-15 12:32                                     ` Josh Boyer
2018-05-15 12:43                                       ` Mimi Zohar
2018-05-01 13:48 ` [PATCH 4/6] ima: coordinate with signed regulatory.db Mimi Zohar
2018-05-01 13:48 ` [PATCH 5/6] ima: verify kernel firmware signatures when using a preallocated buffer Mimi Zohar
2018-05-01 13:48 ` [RFC PATCH 6/6] ima: prevent loading firmware into a pre-allocated buffer Mimi Zohar
2018-05-04  0:10   ` Luis R. Rodriguez

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