linux-kernel - Re: [PATCH v5 3/4] tpm: add SNP SVSM vTPM driver

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Message-ID: <CAGxU2F5WtVZWEgJNwzoWUX0gcq8fe6evnU026R1hHXqCfG2v9w@mail.gmail.com>
Date: Tue, 1 Apr 2025 10:58:41 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: James Bottomley <James.Bottomley@...senpartnership.com>, 
	Dionna Amalie Glaze <dionnaglaze@...gle.com>
Cc: Jarkko Sakkinen <jarkko@...nel.org>, linux-kernel@...r.kernel.org, 
	Jason Gunthorpe <jgg@...pe.ca>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Borislav Petkov <bp@...en8.de>, linux-integrity@...r.kernel.org, Peter Huewe <peterhuewe@....de>, 
	Ingo Molnar <mingo@...hat.com>, linux-coco@...ts.linux.dev, Dov Murik <dovmurik@...ux.ibm.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Joerg Roedel <jroedel@...e.de>, x86@...nel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Claudio Carvalho <cclaudio@...ux.ibm.com>, 
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v5 3/4] tpm: add SNP SVSM vTPM driver

On Tue, 1 Apr 2025 at 00:59, James Bottomley <James.Bottomley@...senpartnership.com> wrote:
>
> On Mon, 2025-03-31 at 15:23 -0700, Dionna Amalie Glaze wrote:
> > On Mon, Mar 31, 2025 at 2:26 PM James Bottomley
> > <James.Bottomley@...senpartnership.com> wrote:
> > >
> > > On Mon, 2025-03-31 at 13:56 -0700, Dionna Amalie Glaze wrote:
> > > [...]
> > > > I might be unclear on how I should be testing this, but I do see
> > > > /dev/tpm0 and /dev/tpmrm0 when I build with CONFIG_TCG_SVSM=y,
> > > > but I don't see the event log in securityfs. What am I missing?
> > >
> > > The vtpm driver for EDK2/OVMF I suspect ... without that the UEFI
> > > won't lay down and event log for the kernel to pick up.
> >
> > This test is with Oliver's PR
> > https://github.com/tianocore/edk2/pull/6527
>
> Well, since the event log is searched for in tpm_chip_register(), I
> really don't think it can be the kernel driver.  Best guess is there's
> something wrong with that patch set (or the vTPM didn't activate in
> OVMF for some reason).

Yep, I also think it should be something in edk2.

I'm using edk2 from https://github.com/coconut-svsm/edk2/pull/62 which 
should contain the commits from that PR + a fix not yet merged upstream.

I'm building it with:
build -a X64 -b DEBUG -t GCC5 -DTPM2_ENABLE \
  --pcd PcdUninstallMemAttrProtocol=TRUE -p OvmfPkg/OvmfPkgX64.dsc

And in Linux I see the devices and the event log:

# ls /dev/tpm*
/dev/tpm0  /dev/tpmrm0

# ls /sys/kernel/security/tpm0/
binary_bios_measurements

# tpm2_eventlog /sys/kernel/security/tpm0/binary_bios_measurements
---
version: 1
events:
- EventNum: 0
  PCRIndex: 0
  EventType: EV_NO_ACTION
  Digest: "0000000000000000000000000000000000000000"
  EventSize: 37
...

If I remove `-DTPM2_ENABLE` when building edk2, I can still see the 
/dev/tpm* devices (of course), but I can't see the event log anymore.
And also most PCRs are 0 (unlike when I have tpm driver enabled in 
edk2).

Thanks,
Stefano