[PATCH 1/1] tpm: clear state post probing

[Ilias Apalodimas]

Hi Heinrich,

On Mon, Nov 15, 2021 at 03:15:45PM +0100, Heinrich Schuchardt wrote:
> Before we can start measuring the TPM must be cleared. Do this in the
> post_probe() method of the uclass.
> 

This looks reasonable to me.  We need to note that this will make the
startup command with 'SU_STATE' argument practically unusable.

OTOH the 'SU_STATE' is supposed to be used on a TPM when the hardware goes
to sleep.  But in order to do so you need to shutdown the TPM with TPM_SU_STATE
as well in order to preserve things like the session counter, PCRs that are 
designated to be saved and restored amongst other things.  I doubt we ever
had proper support for that and I don't think U-Boot needs this
functionality at all(??). So

Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>

> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
>  drivers/tpm/tpm-uclass.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/tpm/tpm-uclass.c b/drivers/tpm/tpm-uclass.c
> index f67fe1019b..9180551d6f 100644
> --- a/drivers/tpm/tpm-uclass.c
> +++ b/drivers/tpm/tpm-uclass.c
> @@ -11,6 +11,7 @@
>  #include <log.h>
>  #include <linux/delay.h>
>  #include <linux/unaligned/be_byteshift.h>
> +#include <tpm_api.h>
>  #include <tpm-v1.h>
>  #include <tpm-v2.h>
>  #include "tpm_internal.h"
> @@ -136,6 +137,26 @@ int tpm_xfer(struct udevice *dev, const uint8_t *sendbuf, size_t send_size,
>  	return 0;
>  }
>  
> +static int dm_tpm_post_probe(struct udevice *dev)
> +{
> +	struct tpm_chip_priv *priv = dev_get_uclass_priv(dev);
> +
> +	/*
> +	 * Clearing the TPM state is only possible once after a hard reset.
> +	 * As we do not know if the TPM has been cleared by a prior boot stage
> +	 * ignore the return value here.
> +	 */
> +	switch (priv->version) {
> +	case TPM_V1:
> +		tpm_startup(dev, TPM_ST_CLEAR);
> +		break;
> +	case TPM_V2:
> +		tpm2_startup(dev, TPM2_SU_CLEAR);
> +		break;
> +	}
> +	return 0;
> +}
> +
>  UCLASS_DRIVER(tpm) = {
>  	.id		= UCLASS_TPM,
>  	.name		= "tpm",
> @@ -143,5 +164,6 @@ UCLASS_DRIVER(tpm) = {
>  #if CONFIG_IS_ENABLED(OF_REAL)
>  	.post_bind	= dm_scan_fdt_dev,
>  #endif
> +	.post_probe	= dm_tpm_post_probe,
>  	.per_device_auto	= sizeof(struct tpm_chip_priv),
>  };
> -- 
> 2.32.0
>