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From: <Alexander.Steffen-d0qZbvYSIPpWk0Htik3J/w@public.gmane.org>
To: jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org
Cc: tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re: [PATCH 1/3] tpm-chip: Move idr_replace calls to appropriate places
Date: Thu, 27 Jul 2017 14:07:49 +0000	[thread overview]
Message-ID: <016fe4c80f0c4b209ac2337500f9dd2b@MUCSE603.infineon.com> (raw)
In-Reply-To: <20170709212430.GB19327-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>

> > diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> > index 67ec9d3..a353b7a 100644
> > +++ b/drivers/char/tpm/tpm-chip.c
> > @@ -327,11 +327,6 @@ static int tpm_add_char_device(struct tpm_chip
> *chip)
> >  		}
> >  	}
> >
> > -	/* Make the chip available. */
> > -	mutex_lock(&idr_lock);
> > -	idr_replace(&dev_nums_idr, chip, chip->dev_num);
> > -	mutex_unlock(&idr_lock);
> 
> This is actually in the wrong place already, it needs to be done before
> cdev_device_add - this is because cdev_device_add generates the uevent to
> userspace which could trigger userspace to use the kernel device. So a patch
> to move it to the start of this function woud be good. The function would be
> better described as 'make visible'

I have looked again at the code and I am not sure this is an issue. The call to idr_replace is only necessary to enable in-kernel usage (i.e. RNG, IMA, ...) of the TPM, but it should not affect userspace in any way. So the location of the idr_replace call does not matter much, as long as the TPM is already initialized. In fact, the main purpose of this patch series (please see PATCH 3/3) is to export the device to userspace without calling idr_replace at all under some circumstances.

Or is there something I missed? The only function that ever tries to access the value stored by idr_replace is tpm_chip_find_get. It is usually called with TPM_ANY_NUM, selecting any TPM that might be present. If no TPM is present (or if idr_replace has not been called) the caller needs to deal with the situation already.

Alexander
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      parent reply	other threads:[~2017-07-27 14:07 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-04 13:56 Alexander Steffen
     [not found] ` <20170704135648.7360-1-Alexander.Steffen-d0qZbvYSIPpWk0Htik3J/w@public.gmane.org>
2017-07-04 13:56   ` [PATCH 2/3] tpm-chip: Return TPM error codes from auto_startup functions Alexander Steffen
2017-07-04 13:56   ` [PATCH 3/3] tpm-chip: Export TPM device to user space even when startup failed Alexander Steffen
2017-07-09 21:24   ` [PATCH 1/3] tpm-chip: Move idr_replace calls to appropriate places Jason Gunthorpe
     [not found]     ` <20170709212430.GB19327-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2017-07-27 14:07       ` Alexander.Steffen-d0qZbvYSIPpWk0Htik3J/w [this message]

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