linux-kernel - Re: [PATCH v3] KEYS: trusted: Use ASN.1 encoded OID

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Date: Thu, 23 May 2024 17:26:19 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, <linux-integrity@...r.kernel.org>
Cc: <keyrings@...r.kernel.org>, "David Woodhouse" <dwmw2@...radead.org>,
 "Eric Biggers" <ebiggers@...nel.org>, "James Bottomley"
 <James.Bottomley@...senpartnership.com>, "Ben Boeckel" <me@...boeckel.net>,
 "David Howells" <dhowells@...hat.com>, "Herbert Xu"
 <herbert@...dor.apana.org.au>, "David S. Miller" <davem@...emloft.net>,
 "Andrew Morton" <akpm@...ux-foundation.org>, "James Bottomley"
 <James.Bottomley@...senPartnership.com>, "Mimi Zohar"
 <zohar@...ux.ibm.com>, "Paul Moore" <paul@...l-moore.com>, "James Morris"
 <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, "open
 list:CRYPTO API" <linux-crypto@...r.kernel.org>, "open list"
 <linux-kernel@...r.kernel.org>, "open list:SECURITY SUBSYSTEM"
 <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v3] KEYS: trusted: Use ASN.1 encoded OID

On Thu May 23, 2024 at 5:20 PM EEST, Jarkko Sakkinen wrote:
> There's no reason to encode OID_TPMSealedData at run-time, as it never
> changes.
>
> Replace it with an encoded u8-array, which has the same number of
> elements:
>
> 	67 81 05 0A 01 05
>
> Include OBJECT IDENTIFIER (0x06) tag and length as the prologue so that
> the OID can be simply copied to the blob leading to:
>
> 	06 06 67 81 05 0A 01 05
>
> Since this in stationary place in the buffer it is guaranteed to always
> fit and not further checks are required.
>
> Reviewed-by: David Howells <dhowells@...hat.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>

Does not really substitute distribution kernel testing, which is
IMHO essential for something like TPM2 boot in systemd but for
simple patches like this, the following does a trivial smoke
test:

export LINUX_OVERRIDE_SRCDIR=<path to a kernel tree with a trusted keys patch>
git clone https://gitlab.com/jarkkojs/linux-tpmdd-test.git
cd linux-tpmdd-test
cmake -Bbuild && make -Cbuild buildroot-prepare
make -Cbuild/buildroot/build
build/buildroot/build/images/run-tests.sh

I'm planning to migrate at some point to systemd and make it
appear more like distribution tho..

For recompiling just kernel only thing needed is:

rm -rf build/buildroot/build/build/linux-custom
make -Cbuild/buildroot/build

I've put this also to the MAINTAINERS entry of TPM driver although
I use it also for keyrings etc. Also it is open for contributions
via Gitlab merge requests (not requesting them per se but I'm open
to such possibility).

BR, Jarkko