linux-kernel - RE: [PATCH] tpm: tpm_crb: relinquish locality on error path.

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Message-ID: <5B8DA87D05A7694D9FA63FD143655C1B94252945@hasmsx108.ger.corp.intel.com>
Date:   Tue, 10 Apr 2018 20:25:26 +0000
From:   "Winkler, Tomas" <tomas.winkler@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>
CC:     "Usyskin, Alexander" <alexander.usyskin@...el.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] tpm: tpm_crb: relinquish locality on error path.

> 
> On Tue, 2018-04-10 at 09:00 +0000, Winkler, Tomas wrote:
> > >
> > > On Sat, 2018-04-07 at 19:12 +0300, Tomas Winkler wrote:
> > > > In crb_map_io() function, __crb_request_locality() is called prior
> > > > to crb_cmd_ready(), but if one of the consecutive function fails
> > > > the flow bails out instead of trying to relinquish locality.
> > > > This patch adds goto jump to __crb_relinquish_locality() on the
> > > > error path.
> > > >
> > > > Fixes: 888d867df441 (tpm: cmd_ready command can be issued only
> > > > after granting
> > > > locality)
> > > > Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
> > > > ---
> > > >  drivers/char/tpm/tpm_crb.c | 10 +++++++---
> > > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/drivers/char/tpm/tpm_crb.c
> > > > b/drivers/char/tpm/tpm_crb.c index 7f78482cd157..34fbc6cb097b
> > > > 100644
> > > > --- a/drivers/char/tpm/tpm_crb.c
> > > > +++ b/drivers/char/tpm/tpm_crb.c
> > > > @@ -511,8 +511,10 @@ static int crb_map_io(struct acpi_device
> > > > *device, struct crb_priv *priv,
> > > >
> > > >  	priv->regs_t = crb_map_res(dev, priv, &io_res, buf-
> > > > >control_address,
> > > >  				   sizeof(struct crb_regs_tail));
> > > > -	if (IS_ERR(priv->regs_t))
> > > > -		return PTR_ERR(priv->regs_t);
> > > > +	if (IS_ERR(priv->regs_t)) {
> > > > +		ret = PTR_ERR(priv->regs_t);
> > > > +		goto out_relinquish_locality;
> > > > +	}
> > > >
> > > >  	/*
> > > >  	 * PTT HW bug w/a: wake up the device to access @@ -520,7 +522,7
> > >
> > > @@
> > > > static int crb_map_io(struct acpi_device *device, struct crb_priv
> > > > *priv,
> > > >  	 */
> > > >  	ret = crb_cmd_ready(dev, priv);
> > > >  	if (ret)
> > > > -		return ret;
> > > > +		goto out_relinquish_locality;
> > > >
> > > >  	pa_high = ioread32(&priv->regs_t->ctrl_cmd_pa_high);
> > > >  	pa_low  = ioread32(&priv->regs_t->ctrl_cmd_pa_low);
> > > > @@ -565,6 +567,8 @@ static int crb_map_io(struct acpi_device
> > > > *device, struct crb_priv *priv,
> > > >
> > > >  	crb_go_idle(dev, priv);
> > > >
> > > > +out_relinquish_locality:
> > > > +
> > > >  	__crb_relinquish_locality(dev, priv, 0);
> > > >
> > > >  	return ret;
> > >
> > > Thanks, please just call it before returning in the error path.
> >
> > Can you please elaborate why, isn't the centralized exiting of
> > functions preferred kernel coding style?
> > https://www.kernel.org/doc/html/v4.11/process/coding-style.html#centra
> > lized-ex
> > iting-of-functions
> 
> You exit only from one location (not multiple) and not from a nested
> context. Here you just add more complexity by doing this.

Where is the complexitity ? I see it as a standard way of undoing on exit.
Tomas