linux-kernel - Re: [PATCH] tpm: fix crash in tpm

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Message-ID: <20160412042627.GA6608@intel.com>
Date:	Tue, 12 Apr 2016 07:26:27 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Peter Huewe <peterhuewe@....de>,
	Marcel Selhorst <tpmdd@...horst.net>,
	"moderated list:TPM DEVICE DRIVER" 
	<tpmdd-devel@...ts.sourceforge.net>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: fix crash in tpm_tis deinitialization

On Mon, Apr 11, 2016 at 11:40:37AM -0600, Jason Gunthorpe wrote:
> On Mon, Apr 11, 2016 at 07:05:20PM +0300, Jarkko Sakkinen wrote:
> > rmmod crashes the driver because tpm_chip_unregister() already sets ops
> > to NULL. This commit fixes the issue by moving tpm2_shutdown() to
> > tpm_chip_unregister(). This commit is also cleanup because it removes
> > duplicate code from tpm_crb and tpm_tis to the core.
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > Fixes: 4d3eac5e156a ("tpm: Provide strong locking for device removal")
> >  drivers/char/tpm/tpm-chip.c | 3 +++
> >  drivers/char/tpm/tpm_crb.c  | 3 ---
> >  drivers/char/tpm/tpm_tis.c  | 3 ---
> >  3 files changed, 3 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> > index f62c851..2642cca 100644
> > +++ b/drivers/char/tpm/tpm-chip.c
> > @@ -361,6 +361,9 @@ void tpm_chip_unregister(struct tpm_chip *chip)
> >  	if (!(chip->flags & TPM_CHIP_FLAG_REGISTERED))
> >  		return;
> >  
> > +	if (chip->flags & TPM_CHIP_FLAG_TPM2)
> > +		tpm2_shutdown(chip, TPM2_SU_CLEAR);
> > +
> >  	if (!(chip->flags & TPM_CHIP_FLAG_TPM2))
> >  		sysfs_remove_link(&chip->dev.parent->kobj, "ppi");
> 
> This needs to be after ops is fenced, something like this.

I would appreciate a supporting argument.

I guess the argument here is that this will prevent user space from
issuing TPM commands after the shutdown command has been sent?

/Jarkko

> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 2642cca05cac..2ea2f1561e59 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -269,6 +269,8 @@ static void tpm_del_char_device(struct tpm_chip *chip)
>  
>  	/* Make the driver uncallable. */
>  	down_write(&chip->ops_sem);
> +	if (chip->flags & TPM_CHIP_FLAG_TPM2)
> +		tpm2_shutdown(chip, TPM2_SU_CLEAR);
>  	chip->ops = NULL;
>  	up_write(&chip->ops_sem);
>  }
> @@ -361,9 +363,6 @@ void tpm_chip_unregister(struct tpm_chip *chip)
>  	if (!(chip->flags & TPM_CHIP_FLAG_REGISTERED))
>  		return;
>  
> -	if (chip->flags & TPM_CHIP_FLAG_TPM2)
> -		tpm2_shutdown(chip, TPM2_SU_CLEAR);
> -
>  	if (!(chip->flags & TPM_CHIP_FLAG_TPM2))
>  		sysfs_remove_link(&chip->dev.parent->kobj, "ppi");
>