Re: [PATCH v5 1/1] tpm: add sysfs exports for all banks of PCR registers

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2021-01-13 at 08:48 +0100, Greg KH wrote:
> On Tue, Jan 12, 2021 at 05:59:58PM -0800, James Bottomley wrote:
> > Create sysfs per hash groups with 24 PCR files in them one group,
> > named pcr-<hash>, for each agile hash of the TPM.  The files are
> > plugged in to a PCR read function which is TPM version agnostic, so
> > this works also for TPM 1.2 but the hash is only sha1 in that case.
> > 
> > Note: the macros used to create the hashes emit spurious checkpatch
> > warnings.  Do not try to "fix" them as checkpatch recommends,
> > otherwise
> > they'll break.
> > 
> > Signed-off-by: James Bottomley <
> > James.Bottomley@HansenPartnership.com>
> > Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> > Tested-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
> > 
> > ---
> > 
> > v2: fix TPM 1.2 legacy links failure
> > v3: fix warn on and add note to tpm_algorithms
> > v4: reword commit and add tested-by
> > v5: algorithm spelling fix WARN->dev_err
> > ---
> >  drivers/char/tpm/tpm-sysfs.c | 179
> > +++++++++++++++++++++++++++++++++++
> >  include/linux/tpm.h          |   9 +-
> >  2 files changed, 187 insertions(+), 1 deletion(-)
> 
> You add new sysfs files, but do not add Documentation/ABI/ entries
> showing how they are used and what they contain :(
> 
> Please do that for the next version of this patch.

It's a bit of a chicken and egg problem since I've no idea when this
will go upstream and the entries require that information making the
ABI more of a post accept type thing.  I can make a guess about the
values if Jarkko is going to but this in for the next merge window.

James

---8>8>8><8<8<8---

From: James Bottomley <James.Bottomley@HansenPartnership.com>
Subject: [PATCH] ABI: add sysfs description for tpm exports of PCR registers

Adds the ABI entries for the new

/sys/class/tpm/tpm<n>/pcr-<hash>/<m>

files which are added to export the PCR hash values on a one value per
file basis.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 Documentation/ABI/stable/sysfs-class-tpm | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-class-tpm b/Documentation/ABI/stable/sysfs-class-tpm
index 91ca63ec7581..d897ecb9615f 100644
--- a/Documentation/ABI/stable/sysfs-class-tpm
+++ b/Documentation/ABI/stable/sysfs-class-tpm
@@ -194,3 +194,17 @@ Description:	The "tpm_version_major" property shows the TCG spec major version
 		Example output::
 
 		  2
+
+What:		/sys/class/tpm/tpmX/pcr-H/N
+Date:		March 2021
+KernelVersion:	5.12
+Contact:	linux-integrity@vger.kernel.org
+Description:	produces output in compact hex representation for PCR
+		number N from hash bank H.  N is the numeric value of
+		the PCR number and H is the crypto string
+		representation of the hash
+
+		Example output::
+
+		  cat /sys/class/tpm/tpm0/pcr-sha256/7
+		  2ED93F199692DC6788EFA6A1FE74514AB9760B2A6CEEAEF6C808C13E4ABB0D42