linux-kernel - Re: [PATCH] mtd: spi-nor: intel-spi: Do not try to make the SPI flash chip writable

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Date:   Mon, 24 Aug 2020 13:00:42 -0300
From:   Daniel Gutson <daniel@...ypsium.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alex Bazhaniuk <alex@...ypsium.com>,
        Richard Hughes <hughsient@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] mtd: spi-nor: intel-spi: Do not try to make the SPI flash
 chip writable

On Mon, Aug 24, 2020 at 6:44 AM Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
>
> On Mon, Aug 24, 2020 at 11:31:40AM +0200, Arnd Bergmann wrote:
> > On Mon, Aug 24, 2020 at 11:15 AM Mika Westerberg
> > <mika.westerberg@...ux.intel.com> wrote:
> > > On Mon, Aug 24, 2020 at 11:08:33AM +0200, Arnd Bergmann wrote:
> > > > On Mon, Aug 24, 2020 at 10:22 AM Mika Westerberg
> > > > <mika.westerberg@...ux.intel.com> wrote:
> > > > > On Sat, Aug 22, 2020 at 06:06:03PM +0200, Arnd Bergmann wrote:
> > > > > > On Wed, Aug 19, 2020 at 11:11 AM Mika Westerberg
> > > > > >
> > > > > > The mtd core just checks both the permissions on the device node (which
> > > > > > default to 0600 without any special udev rules) and the MTD_WRITEABLE
> > > > > > on the underlying device that is controlled by the module parameter
> > > > > > in case of intel-spi{,-platform,-pci}.c.
> > > > >
> > > > > OK, thanks.
> > > > >
> > > > > Since we cannot really get rid of the module parameter (AFAIK there are
> > > > > users for it), I still think we should just make the "writeable" to
> > > > > apply to the PCI part as well. That should at least make it consistent,
> > > > > and it also solves Daniel's case.
> > > >
> > > > Can you explain Daniel's case then? I still don't understand what he
> > > > actually wants.
> > > >
> > > > As I keep repeating, the module parameter *does* apply to the pci
> > > > driver front-end since it determines whether the driver will disallow
> > > > writes to the mtd device without it. The only difference is that the pci
> > > > driver will attempt to set the hardware bit without checking the
> > > > module parameter first, while the platform driver does not. If the
> > > > module parameter is not set however, the state of the hardware
> > > > bit is never checked again.
> > >
> > > I think Daniel wants the PCI driver not to set the hardware bit by
> > > default (same as the platform driver).
> >
> > Sure, but *why*?
>
> Because this is part of the platform firmware security check patch he is
> also working on and, I guess making the flash chip writeable by default
> is triggering some of the checks in that patch. Or something along those
> lines ;-)

Correct. I need these drivers to be enabled by default, but they are
documented as "DANGEROUS", so I want to also split the driver
in read-only mode and R/W mode. Currently, the driver is R/W,
and this would be a little first step in that direction.

-- 
Daniel Gutson
Argentina Site Director
Enginieering Director
Eclypsium

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