linux-kernel - Re: [Regression] TPM char device not created if TPM 1.2 is disabled, but visible

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Message-ID: <7A0881B1-6581-4D0B-A4A9-B014F995B338@fb.com>
Date:   Mon, 5 Mar 2018 19:28:26 +0000
From:   Sahil Rihan <srihan@...com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexei Starovoitov" <ast@...com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Subject: Re: [Regression] TPM char device not created if TPM 1.2 is disabled,
 but visible

> On Sat, Mar 03, 2018 at 09:27:36PM +0000, Sahil Rihan wrote:
> > (Please CC me on replies - I'm not subscribed to LMKL)
> > 
> > Prior to  0cf577a03f21 if a TPM 1.2 device was disabled, but visible (sysfs node "enabled" returns 0), creation of the TPM char device was only skipped if  tpm_bios_log_setup returned -ENODEV. 
> > 
> > On some systems like HP DL380 G9, if the TPM is disabled but visible, the TCPA log is empty, which means tpm_read_log_acpi returns -EIO.  Starting with 0cf577a03f21, -EIO triggers an early return from tpm_chip_register which means the char device is not created.
> > 
> > Log snippet:
> > [    4.320387] tpm_tis 00:00: 1.2 TPM (device-id 0xB, rev-id 16)
> > [    4.455389] tpm tpm0: A TPM error (7) occurred attempting to read a pcr value
> > [    4.457762] tpm tpm0: TPM is disabled/deactivated (0x7)
> > [    4.459461] tpm tpm0: tpm_read_log_acpi: TCPA log area empty    <----------------------
> > [    4.461312] tpm_tis: probe of 00:00 failed with error -5
> > 
> > Thanks,
> > Sahil
>
> Thanks for the bug report, I appreciate it!
> 
> Personally I think we should keep the warning if the log area is empt
> but tpm_read_log_acpi() should return -ENODEV in this case.
> 
> /Jarkko

Agree on keeping the warning. 

I'm guessing you want to return -ENODEV from tpm_bios_log_setup. Doing it from tpm_read_log_acpi will just fall through to calling tpm_read_log_of, which I think will end up returning -EIO again.

In terms of semantics I'm not sure if -ENODEV is the right return code if the BIOS event log is absent. I guess you can claim it's some sort of "device". I don’t have a strong opinion here.

Sahil