Re: [PATCH v7 4/4] optee: probe RPMB device using RPMB subsystem

[Manuel Traut <manut@mecka.net>]

On Thu, May 30, 2024 at 11:29:11AM +0300, Mikko Rapeli wrote:
> On Thu, May 30, 2024 at 09:35:10AM +0200, Manuel Traut wrote:
> > Hi Mikko,
> > 
> > On Wed, May 29, 2024 at 05:26:15PM +0300, Mikko Rapeli wrote:
> > > Hi,
> > > 
> > > On Wed, May 29, 2024 at 11:38:06AM +0200, Manuel Traut wrote:
> > > > Hi Mikko,
> > > > 
> > > > On 10:09 Wed 29 May     , Mikko Rapeli wrote:
> > > > > On Wed, May 29, 2024 at 10:56:04AM +0530, Sumit Garg wrote:
> > > > > > On Tue, 28 May 2024 at 15:00, Mikko Rapeli <mikko.rapeli@linaro.org> wrote:
> > > > > > > On Mon, May 27, 2024 at 03:24:01PM +0200, Jens Wiklander wrote:
> > > > > > > > On Mon, May 27, 2024 at 3:00 PM Jerome Forissier
> > > > > > > > <jerome.forissier@linaro.org> wrote:
> > > > > > > > > On 5/27/24 14:13, Jens Wiklander wrote:
> > > > > > > Outside of these patches, I think the optee RPC setup with fTPM TA is one area which
> > > > > > > currently requires tee-supplicant to be started. Detecting the existence of TPM before
> > > > > > > kernel drivers are loaded is possible via the exported EFI logs from firmware to kernel
> > > > > > > or ACPI TPM2 table entry, and detecting optee and thus starting tee-supplicant in userspace too.
> > > > > > 
> > > > > > One thing I am trying to find an answer about is why do we need to
> > > > > > defer tee-supplicant launch if it's bundled into initrd? Once you
> > > > > > detect OP-TEE then tee-supplicant should be launched unconditionally.
> > > > > > As per your example below, the motivation here seems to be the TPM2
> > > > > > device dependent on RPMB backend but what if other future systemd
> > > > > > services come up and depend on other services offered by
> > > > > > tee-supplicant?
> > > > > 
> > > > > There is an annoying depedency between firmware side optee and TAs, and kernel optee driver,
> > > > > tee-supplicant in userspace and kernel TA drivers like fTPM.
> > > > > 
> > > > > Kernel fTPM driver and fTPM TA require tee-supplicant in userspace for RPMB, RPC etc.
> > > > > 
> > > > > This patch series is adding kernel side support for RPMB handling so that the dependency to
> > > > > tee-supplicant in userspace can be removed. For fTPM use case, there is still the optee RPC
> > > > > buffer setup which currently requires tee-supplicant in userspace or fTPM TA will panic.
> > > > > 
> > > > > So yes, currently, tee-supplicant must be started. But it would be great if kernel drivers
> > > > > and firmware optee trusted applications would not depend on tee-supplicant running in userspace.
> > > > > The startup sequence is really tricky to get right. My fTPM use case is using the TPM device
> > > > > to encrypt rootfs and thus all SW components including tee-supplicant need to run early in
> > > > > initramfs. Currently also switch from initramfs to main rootfs requires unloading
> > > > > fTPM kernel driver and stopping tee-supplicant in initrd, and then starting tee-supplicant
> > > > > and loading fTPM kernel driver from main rootfs. udev and automatic module loading for
> > > > > fTPM can not be used due to the tee-supplicant userspace dependency.
> > > > 
> > > > I decided to build fTPM as buildin-TA into OP-TEE. RPMB routing is already
> > > > implemented in u-boot so it can already write PCR registers.
> > > 
> > > Is build in TA same as early TA? I presume so.
> > 
> > Indeed.. sorry for using the wrong term.
> 
> Ok, no problem. Then we have the same fTPM TA setup. I'm using optee 4.1
> with RPMB kernel support changes from Jens cherry-picked on top.
> 
> > > > With this series and the required changes in OP-TEE and a compiled in fTPM
> > > > kernel driver and systemd v256 it is possible to use the fTPM in the initrd
> > > > without tee-supplicant.
> > > > 
> > > > Maybe this information is helpful to you, regards
> > > 
> > > This is very interesting and I'm trying to get to the same state, though with
> > > fTPM kernel driver as module. With v6 of this patch set and matching optee changes
> > > I was not able to make this work as fTPM TA was crashing when loading ftpm kernel driver
> > > due to failing RPC allocation, which tee-supplicant was setting up in the whole chain.
> > > I'll try to get v7 patches working and test this again on my yocto based setup and kernel 6.6.y.
> > 
> > I'll try today also with v7 and 6.10-rc1 on an i.MX8MM. It should also
> > work with fTPM as kernel module if you use systemd in the initrd
> > with the new tpm.target in systemd v256.
> 
> Thanks for the details. I'm testing on qemu, rockpi4b (Rockchip rk3399 SoC) and synquacer
> (Socionext Developer Box, SC2A11:Cortex-A53 MPCore 24cores). Kernel and rootfs
> are from our yocto master branch based Trusted Reference Stack distro
> ( https://gitlab.com/Linaro/trusted-reference-stack/trs )
> with kernel 6.6.29 (porting the RPMB v7 patches currently), systemd 255.4 (tpm2.target
> backported), tee-supplicant 4.1 etc. I'm switching the initramfs from shell scripts
> to systemd currently, but running into various issues.

I just use a mkosi generated Debian/sid image..

> UEFI firmware is our Trusted Substrate ( https://gitlab.com/Linaro/trustedsubstrate/meta-ts/ )

This is a cool project! I was not aware of it. Thanks for sharing.

> ARM System Ready IR compatible with secure boot and TPM support, u-boot
> 2024.04 (except rockpi4b still on 2023.01), optee 4.1, fTPM etc from meta-arm
> yocto layer.

I am on a Toradex Verdin board with an i.MX8MM SoM. u-boot is still
2024.01, optee_os from Jens referenced branch, with a little change in:

lib/libutee/include/user_ta_header.h

-#define TA_FLAGS_MASK  GENMASK_32(10, 0)
+#define TA_FLAGS_MASK  GENMASK_32(12, 0)

fTPM is from ms-tpm-20-ref.git on github. Need to check what is in the meta-arm.
Figured out some problems with this regarding OrPolicies used by
systemd-cryptenroll..

> Booting without tee-supplicant has so far only resulted in the fTPM TA panic'ing
> because RPC setup is failing. Also the fTPM TA enumation needs to be changed
> from current yocto defaults to always discoverable if there is no tee-supplicant:
> https://git.yoctoproject.org/meta-arm/tree/meta-arm/recipes-security/optee-ftpm/optee-ftpm/0001-add-enum-to-ta-flags.patch

Ah, seems to be the same change than above, just limited to the fTPM TA?
Shouldn't it be part of optee_os since it is a capability of it?

> I hope to get v7 of these patches into testing today.

Was able to test it. But ended also in TA panic. Will share the details
in another mail.

Regards
Manuel