From mboxrd@z Thu Jan  1 00:00:00 1970
From: zohar@linux.vnet.ibm.com (Mimi Zohar)
Date: Wed, 08 Nov 2017 21:17:37 -0500
Subject: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel
	lockdown
In-Reply-To: <20171109014841.GF7859@linaro.org>
References: <1509660086.3416.15.camel@linux.vnet.ibm.com>
	<150842463163.7923.11081723749106843698.stgit@warthog.procyon.org.uk>
	<14219.1509660259@warthog.procyon.org.uk>
	<1509660641.3416.24.camel@linux.vnet.ibm.com>
	<20171107230700.GJ22894@wotan.suse.de>
	<20171108061551.GD7859@linaro.org>
	<20171108194626.GQ22894@wotan.suse.de>
	<20171109014841.GF7859@linaro.org>
Message-ID: <1510193857.4484.95.camel@linux.vnet.ibm.com>
To: linux-security-module@vger.kernel.org
List-Id: linux-security-module.vger.kernel.org

> > IMHO that should just fail then, ie, a "locked down" kernel should not want to
> > *pass* a firmware signature if such thing could not be done.
> > 
> > Its no different than trying to verify a signed module on a "locked down" for
> > which it has no signature.
> > 
> > But perhaps I'm not understanding the issue well, let me know.
> 
> My point is quite simple:
> my_deviceA_init() {
>         err = request_firmware(&fw, "deviceA"); <--- (a)
>         if (err)
>                 goto err_request;
> 
>         err = verify_firmware(fw);  <--- (b)
>         if (err)
>                 goto err_verify;
> 
>         load_fw_to_deviceA(fw);     <--- (c)
>         ...
> }
> 
> As legacy device drivers does not have (b), there is no chance to
> prevent loading a firmware at (c) for locked-down kernel.
> 
> If you allow me to bring in yet another function, say
> request_firmware_signable(), which should be used in place of (a)
> for all verification-aware drivers, that would be fine.

I really don't understand why you need a new function.??The
request_firmware() eventually calls kernel_read_file_from_path(),
which already calls the pre and post LSM hooks.

IMA-appraisal is already on these hooks verifying the requested
firmware's signature. ?For systems with "lockdown" enabled, but
without IMA-appraisal enabled, define a small, builtin LSM that sits
on these LSM hooks and denies the unsigned firmware requests.

Mimi

> In this case, all the invocation of request_firmware() in legacy code
> could be forced to fail in locked-down kernel.
> 
> But I think that "signable" should be allowed to be combined with other
> features of request_firmware variants like _(no)wait or _direct.
> 
> -Takahiro AKASHI

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