linux-kernel - Re: ima - wait for tpm load

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Date:   Thu, 10 Jun 2021 16:31:13 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     "Jorge Ramirez-Ortiz, Foundries" <jorge@...ndries.io>
Cc:     dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jarkko Sakkinen <jarkko@...nel.org>
Subject: Re: ima - wait for tpm load

On Thu, 2021-06-10 at 17:18 +0200, Jorge Ramirez-Ortiz, Foundries
wrote:
> On 10/06/21, Mimi Zohar wrote:
> > [Cc'ing Jarkko]
> > 
> > On Thu, 2021-06-10 at 09:16 +0200, Jorge Ramirez-Ortiz, Foundries
> > wrote:
> > > I am enabling IMA on a ZynqMP based platform using an SPI based TPM
> > > from Infineon.
> > > 
> > > The SPI TPM driver is built-in but since the IMA is initalized from a
> > > late_initcall, IMA never finds the TPM.
> > > 
> > > Is there a recomended way to work around this issue?
> > > 
> > > fio@...cg-dwg:~$ dmesg | grep tpm
> > > [    3.381181] tpm_tis_spi spi1.1: 2.0 TPM (device-id 0x1B, rev-id 22)
> > > [    3.423608] tpm tpm0: A TPM error (256) occurred attempting the self test
> > > [    3.430406] tpm tpm0: starting up the TPM manually
> > > 
> > > fio@...cg-dwg:~$ dmesg | grep ima
> > > [    3.525741] ima: No TPM chip found, activating TPM-bypass!
> > > [    3.531233] ima: Allocated hash algorithm: sha1
> > 
> > Lengthening the TPM timeout, executing the TPM self test have been past
> > reasons for the TPM not to initialize prior to IMA.
> 
> right, I can understand this.
> 
> The problem in this case is that tpm_chip_register() is taking too
> long so by the time it executes tpm_add_char_device(chip) is called,
> ima has already given up.
> 
> The way I am working around this is just by adding a new flag and
> providing the chip in idr_alloc (so ima can find it).
> 
> Then add an 'enable' flag to the chip structure that ima can use to
> wait on.
> 
> @@ -333,8 +345,13 @@ struct tpm_chip *tpm_chip_alloc(struct device *pdev,
> 
>         chip->ops = ops;
> 
> + if (ops->flags & TPM_OPS_SLOW_STARTUP)
> +         chip->flags |= TPM_CHIP_FLAG_SLOW_STARTUP;
> +
>         mutex_lock(&idr_lock);
> -   rc = idr_alloc(&dev_nums_idr, NULL, 0, TPM_NUM_DEVICES, GFP_KERNEL);
> + rc = idr_alloc(&dev_nums_idr,
> +                chip->flags & TPM_CHIP_FLAG_SLOW_STARTUP ? chip : NULL,
> +                0, TPM_NUM_DEVICES, GFP_KERNEL);
>         mutex_unlock(&idr_lock);
>         if (rc < 0) {
>                 dev_err(pdev, "No available tpm device numbers\n");

As I recall "extend" works pretty much from the beginning.  There's no
need to wait for the self test to complete.   Registering the TPM early
might be enough without having to wait.  Or maybe check the selftest
result.

Thank you for looking into resolving this problem!

Mimi

> 
> 
> > 
> > (Missing from this bug report is the kernel version.)
> 
> um, didnt think of it as a bug report - the feature is clearly not
> synchronized so there can be no guarantees about available TPMs being
> used. 
> 
> but yes, this is happening on 5.10.42 using tpm_tis_spi to connect to
> infineon SLM9670