linux-kernel - Re: [PATCH] tpm_crb: Add idle support for the Arm FF-A start method

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Message-ID: <aKzoaWeJOh5W0M6J@kernel.org>
Date: Tue, 26 Aug 2025 01:49:13 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stuart Yoder <stuart.yoder@....com>
Cc: linux-integrity@...r.kernel.org, peterhuewe@....de, jgg@...pe.ca,
	sudeep.holla@....com, Prachotan.Bathi@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm_crb: Add idle support for the Arm FF-A start method

On Mon, Aug 25, 2025 at 05:19:34PM -0500, Stuart Yoder wrote:
> 
> 
> On 8/25/25 4:58 PM, Jarkko Sakkinen wrote:
> > On Mon, Aug 25, 2025 at 03:59:43PM -0500, Stuart Yoder wrote:
> > > According to the CRB over FF-A specification [1], a TPM that implements
> > > the ABI must comply with the TCG PTP specification. This requires support
> > > for the Idle and Ready states.
> > > 
> > > This patch implements CRB control area requests for goIdle and
> > > cmdReady on FF-A based TPMs.
> > > 
> > > The FF-A message used to notify the TPM of CRB updates includes a
> > > locality parameter, which provides a hint to the TPM about which
> > > locality modified the CRB.  This patch adds a locality parameter
> > > to __crb_go_idle() and __crb_cmd_ready() to support this.
> > > 
> > > [1] https://developer.arm.com/documentation/den0138/latest/
> > > 
> > > Signed-off-by: Stuart Yoder <stuart.yoder@....com>
> > 
> > Perhaps a dummy question but is this "QEMU testable"? I know how
> > to bind swtpm to QEMU and make it appear as CRB device on x86-64.
> > 
> > I don't see much testing happening with these ARM CRB patches,
> > and if that works in the first palce  I could probably add
> > a new board target to my BR2_EXTERNAL [1].
> > 
> > I can of course do "negative testing' i.e. that these don't
> > break x86 ;-)
> 
> Unfortunately this is not currently testable on QEMU.  We are using
> the Arm FVP [1], which is also a machine emulator, with the firmware
> stack and an fTPM running in TrustZone.  The firmware, fTPM, etc are
> not all publicly available yet, but everything is based on open
> source projects and the intent is that all the components needed do
> test this on FVP will be available at some point.
> 
> There is nothing fundamental that would prevent this from running
> on QEMU, but just a fair amount of integration and possibly firmware
> work.

OK, it's cool and the patch looks totally fine and I can
"hallucinate it" so:

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

> 
> [1] https://developer.arm.com/Tools%20and%20Software/Fixed%20Virtual%20Platforms/Arm%20Architecture%20FVPs
> 
> Thanks,
> Stuart

BR, Jarkko