linux-kernel - RE: [patch v3 1/3] drivers: jtag: Add JTAG core driver

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Date:   Wed, 16 Aug 2017 14:24:16 +0000
From:   Oleksandr Shamray <oleksandrs@...lanox.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     gregkh <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Joel Stanley <joel@....id.au>,
        Jiří Pírko <jiri@...nulli.us>,
        Tobias Klauser <tklauser@...tanz.ch>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "mec@...ut.net" <mec@...ut.net>,
        "vadimp@...llanox.com" <vadimp@...llanox.com>,
        system-sw-low-level <system-sw-low-level@...lanox.com>,
        Rob Herring <robh+dt@...nel.org>,
        "openocd-devel-owner@...ts.sourceforge.net" 
        <openocd-devel-owner@...ts.sourceforge.net>,
        Jiri Pirko <jiri@...lanox.com>
Subject: RE: [patch v3 1/3] drivers: jtag: Add JTAG core driver

> -----Original Message-----
> From: arndbergmann@...il.com [mailto:arndbergmann@...il.com] On
> Behalf Of Arnd Bergmann
> Sent: Tuesday, August 15, 2017 2:16 PM
> To: Oleksandr Shamray <oleksandrs@...lanox.com>
> Cc: gregkh <gregkh@...uxfoundation.org>; Linux Kernel Mailing List <linux-
> kernel@...r.kernel.org>; Linux ARM <linux-arm-kernel@...ts.infradead.org>;
> devicetree@...r.kernel.org; OpenBMC Maillist <openbmc@...ts.ozlabs.org>;
> Joel Stanley <joel@....id.au>; Jiří Pírko <jiri@...nulli.us>; Tobias Klauser
> <tklauser@...tanz.ch>; linux-serial@...r.kernel.org; mec@...ut.net;
> vadimp@...llanox.com; system-sw-low-level <system-sw-low-
> level@...lanox.com>; Rob Herring <robh+dt@...nel.org>; openocd-devel-
> owner@...ts.sourceforge.net; Jiri Pirko <jiri@...lanox.com>
> Subject: Re: [patch v3 1/3] drivers: jtag: Add JTAG core driver
> 
> On Tue, Aug 15, 2017 at 12:00 PM, Oleksandr Shamray
> <oleksandrs@...lanox.com> wrote:
> 
> > +       case JTAG_IOCXFER:
> > +               if (copy_from_user(&xfer, varg, sizeof(struct jtag_xfer)))
> > +                       return -EFAULT;
> > +
> > +               if (xfer.length >= JTAG_MAX_XFER_DATA_LEN)
> > +                       return -EFAULT;
> > +
> > +               user_tdio_data = xfer.tdio;
> > +               xfer.tdio = jtag_copy_from_user((void __user *)user_tdio_data,
> > +                                               xfer.length);
> > +               if (!xfer.tdio)
> > +                       return -ENOMEM;
> 
> This is not safe for 32-bit processes on 64-bit kernels, since the structure layout
> differs for the pointer member. It's better to always use either rework the
> structure to avoid the pointer, or to use a
> __u64 member to store it, and then use u64_to_user_ptr() to convert it in the
> kernel.

Thanks,  I think using __u64 instead of  pointer will be a good solution.

> 
> > +       case JTAG_GIOCSTATUS:
> > +               if (jtag->ops->status_get)
> > +                       err = jtag->ops->status_get(jtag,
> > +                                               (enum jtag_endstate
> > + *)&value);
> 
> This pointer cast is also not safe, as an enum might have a different size than
> the 'value' variable that is not an enum. I think you need to change the
> argument type for the callback, or maybe use another intermediate.
> 
> > +static int jtag_open(struct inode *inode, struct file *file) {
> > +       struct jtag *jtag = container_of(inode->i_cdev, struct jtag,
> > +cdev);
> > +
> > +       spin_lock(&jtag->lock);
> > +
> > +       if (jtag->is_open) {
> > +               dev_info(NULL, "jtag already opened\n");
> > +               spin_unlock(&jtag->lock);
> > +               return -EBUSY;
> > +       }
> > +
> > +       jtag->is_open = true;
> > +       file->private_data = jtag;
> > +       spin_unlock(&jtag->lock);
> > +       return 0;
> > +}
> 
> Does the 'is_open' flag protect you from something that doesn't also happen
> after a 'dup()' call on the file descriptor?

is_open flag protects from the opening file more than one time.

> 
> > + * @mode: access mode
> > + * @type: transfer type
> > + * @direction: xfer direction
> > + * @length: xfer bits len
> > + * @tdio : xfer data array
> > + * @endir: xfer end state
> > + *
> > + * Structure represents interface to Aspeed JTAG device for jtag sdr
> > +xfer
> > + * execution.
> > + */
> > +struct jtag_xfer {
> > +       __u8    mode;
> > +       __u8    type;
> > +       __u8    direction;
> > +       __u32   length;
> > +       __u8    *tdio;
> > +       __u8    endstate;
> > +};
> 
> As mentioned above, the pointer in here makes it incompatible. Also, you
> should reorder the members to avoid the implied padding.
> Moving the 'endstate' before 'length' is sufficient.
> 

Thank. I will do it.

>         Arnd