linux-kernel - Re: [PATCH] tpm: Revert "tpm: fix invalid locking in NONBLOCKING mode"

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Message-ID: <da3027a2aa9d1b7110a65de919e88f42ef2e13bb.camel@guzman.io>
Date:   Tue, 26 May 2020 15:19:32 -0700
From:   Alex Guzman <alex@...man.io>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Mario.Limonciello@...l.com, peterhuewe@....de,
        jarkko.sakkinen@...ux.intel.com, jgg@...pe.ca
Cc:     arnd@...db.de, gregkh@...uxfoundation.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        jeffrin@...agiritech.edu.in
Subject: Re: [PATCH] tpm: Revert "tpm: fix invalid locking in NONBLOCKING
 mode"

On Tue, 2020-05-26 at 12:38 -0700, James Bottomley wrote:
> On Tue, 2020-05-26 at 19:23 +0000, Mario.Limonciello@...l.com wrote:
> > > On Tue, 2020-05-26 at 13:32 -0500, Mario Limonciello wrote:
> > > > This reverts commit d23d12484307b40eea549b8a858f5fffad913897.
> > > > 
> > > > This commit has caused regressions for the XPS 9560 containing
> > > > a Nuvoton TPM.
> > > 
> > > Presumably this is using the tis driver?
> > 
> > Correct.
> > 
> > > > As mentioned by the reporter all TPM2 commands are failing
> > > > with:
> > > >   ERROR:tcti:src/tss2-tcti/tcti-
> > > > device.c:290:tcti_device_receive()
> > > >   Failed to read response from fd 3, got errno 1: Operation not
> > > > permitted
> > > > 
> > > > The reporter bisected this issue back to this commit which was
> > > > backported to stable as commit 4d6ebc4.
> > > 
> > > I think the problem is request_locality ... for some inexplicable
> > > reason a failure there returns -1, which is EPERM to user space.
> > > 
> > > That seems to be a bug in the async code since everything else
> > > gives a ESPIPE error if tpm_try_get_ops fails ... at least no-one
> > > assumes it gives back a sensible return code.
> > > 
> > > What I think is happening is that with the patch the TPM goes
> > > through a quick sequence of request, relinquish, request,
> > > relinquish and it's the third request which is failing (likely
> > > timing out).  Without the patch, the patch there's only one
> > > request,relinquish cycle because the ops are held while the async
> > > work is executed.  I have a vague recollection that there is a
> > > problem with too many locality request in quick succession, but
> > > I'll defer to Jason, who I think understands the intricacies of
> > > localities better than I do.
> > 
> > Thanks, I don't pretend to understand the nuances of this
> > particular
> > code, but I was hoping that the request to revert got some
> > attention
> > since Alex's kernel Bugzilla and message a few months ago to linux
> > integrity weren't.
> > 
> > > If that's the problem, the solution looks simple enough: just
> > > move
> > > the ops get down because the priv state is already protected by
> > > the
> > > buffer mutex
> > 
> > Yeah, if that works for Alex's situation it certainly sounds like a
> > better solution than reverting this patch as this patch actually
> > does
> > fix a problem reported by Jeffrin originally.
> > 
> > Could you propose a specific patch that Alex and Jeffrin can
> > perhaps
> > both try?
> 
> Um, what's wrong with the one I originally attached and which you
> quote
> below?  It's only compile tested, but I think it will work, if the
> theory is correct.
> 
> James
> 
> > > James
> > > 
> > > ---
> > > 
> > > diff --git a/drivers/char/tpm/tpm-dev-common.c
> > > b/drivers/char/tpm/tpm-dev-
> > > common.c
> > > index 87f449340202..1784530b8387 100644
> > > --- a/drivers/char/tpm/tpm-dev-common.c
> > > +++ b/drivers/char/tpm/tpm-dev-common.c
> > > @@ -189,15 +189,6 @@ ssize_t tpm_common_write(struct file *file,
> > > const char
> > > __user *buf,
> > >  		goto out;
> > >  	}
> > > 
> > > -	/* atomic tpm command send and result receive. We only
> > > hold the ops
> > > -	 * lock during this period so that the tpm can be
> > > unregistered even if
> > > -	 * the char dev is held open.
> > > -	 */
> > > -	if (tpm_try_get_ops(priv->chip)) {
> > > -		ret = -EPIPE;
> > > -		goto out;
> > > -	}
> > > -
> > >  	priv->response_length = 0;
> > >  	priv->response_read = false;
> > >  	*off = 0;
> > > @@ -211,11 +202,19 @@ ssize_t tpm_common_write(struct file *file,
> > > const char
> > > __user *buf,
> > >  	if (file->f_flags & O_NONBLOCK) {
> > >  		priv->command_enqueued = true;
> > >  		queue_work(tpm_dev_wq, &priv->async_work);
> > > -		tpm_put_ops(priv->chip);
> > >  		mutex_unlock(&priv->buffer_mutex);
> > >  		return size;
> > >  	}
> > > 
> > > +	/* atomic tpm command send and result receive. We only
> > > hold the ops
> > > +	 * lock during this period so that the tpm can be
> > > unregistered even if
> > > +	 * the char dev is held open.
> > > +	 */
> > > +	if (tpm_try_get_ops(priv->chip)) {
> > > +		ret = -EPIPE;
> > > +		goto out;
> > > +	}
> > > +
> > >  	ret = tpm_dev_transmit(priv->chip, priv->space, priv-
> > > > data_buffer,
> > > 
> > >  			       sizeof(priv->data_buffer));
> > >  	tpm_put_ops(priv->chip);

When using your patch, I get a hang when trying to use tpm2_getcap, and
dmesg shows some info.



View attachment "buglog.txt" of type "text/plain" (3761 bytes)