[PATCH] mtd: spi-nor: intel-spi: Split intel-spi reading from writing

[Daniel Gutson]

On Thu, Oct 29, 2020 at 2:40 AM Greg Kroah-Hartman
<gregkh at linuxfoundation.org> wrote:
>
> On Wed, Oct 28, 2020 at 06:43:59PM -0300, Daniel Gutson wrote:
> > This patch separates the writing part of the intel-spi drivers
> > so the 'dangerous' part can be set/unset independently.
> > This way, the kernel can be configured to include the reading
> > parts of the driver which can be used without
> > the dangerous write operations that can turn the system
> > unbootable.
> >
> > Signed-off-by: Daniel Gutson <daniel.gutson at eclypsium.com>
> > ---
> >  drivers/mtd/spi-nor/controllers/Kconfig     | 39 ++++++++++++---------
> >  drivers/mtd/spi-nor/controllers/intel-spi.c | 12 +++++--
> >  2 files changed, 33 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/mtd/spi-nor/controllers/Kconfig b/drivers/mtd/spi-nor/controllers/Kconfig
> > index 5c0e0ec2e6d1..491c755fea49 100644
> > --- a/drivers/mtd/spi-nor/controllers/Kconfig
> > +++ b/drivers/mtd/spi-nor/controllers/Kconfig
> > @@ -31,34 +31,41 @@ config SPI_INTEL_SPI
> >       tristate
> >
> >  config SPI_INTEL_SPI_PCI
> > -     tristate "Intel PCH/PCU SPI flash PCI driver (DANGEROUS)"
> > +     tristate "Intel PCH/PCU SPI flash PCI driver"
> >       depends on X86 && PCI
> >       select SPI_INTEL_SPI
> >       help
> > -       This enables PCI support for the Intel PCH/PCU SPI controller in
> > -       master mode. This controller is present in modern Intel hardware
> > -       and is used to hold BIOS and other persistent settings. Using
> > -       this driver it is possible to upgrade BIOS directly from Linux.
> > -
> > -       Say N here unless you know what you are doing. Overwriting the
> > -       SPI flash may render the system unbootable.
> > +       This enables read only PCI support for the Intel PCH/PCU SPI
> > +       controller in master mode. This controller is present in modern
> > +       Intel hardware and is used to hold BIOS and other persistent settings.
> > +       Using this driver it is possible to read the SPI chip directly
> > +       from Linux.
> >
> >         To compile this driver as a module, choose M here: the module
> >         will be called intel-spi-pci.
> >
> >  config SPI_INTEL_SPI_PLATFORM
> > -     tristate "Intel PCH/PCU SPI flash platform driver (DANGEROUS)"
> > +     tristate "Intel PCH/PCU SPI flash platform driver"
> >       depends on X86
> >       select SPI_INTEL_SPI
> >       help
> > -       This enables platform support for the Intel PCH/PCU SPI
> > +       This enables read only platform support for the Intel PCH/PCU SPI
> >         controller in master mode. This controller is present in modern
> > -       Intel hardware and is used to hold BIOS and other persistent
> > -       settings. Using this driver it is possible to upgrade BIOS
> > -       directly from Linux.
> > +       Intel hardware and is used to hold BIOS and other persistent settings.
> > +       Using this driver it is possible to read the SPI chip directly
> > +       from Linux.
> > +
> > +       To compile this driver as a module, choose M here: the module
> > +       will be called intel-spi-pci.
> > +
> > +config SPI_INTEL_SPI_WRITE
> > +     bool "Intel PCH/PCU SPI flash drivers write operations (DANGEROUS)"
> > +     depends on SPI_INTEL_SPI_PCI || SPI_INTEL_SPI_PLATFORM
> > +     help
> > +       This enables full read/write support for the Intel PCH/PCU SPI
> > +       controller.
> > +       Using this option it may be possible to upgrade BIOS directly
> > +       from Linux.
> >
> >         Say N here unless you know what you are doing. Overwriting the
> >         SPI flash may render the system unbootable.
> > -
> > -       To compile this driver as a module, choose M here: the module
> > -       will be called intel-spi-platform.
> > diff --git a/drivers/mtd/spi-nor/controllers/intel-spi.c b/drivers/mtd/spi-nor/controllers/intel-spi.c
> > index b54a56a68100..8d8053395c3d 100644
> > --- a/drivers/mtd/spi-nor/controllers/intel-spi.c
> > +++ b/drivers/mtd/spi-nor/controllers/intel-spi.c
> > @@ -266,6 +266,7 @@ static int intel_spi_read_block(struct intel_spi *ispi, void *buf, size_t size)
> >       return 0;
> >  }
> >
> > +#ifdef CONFIG_SPI_INTEL_SPI_WRITE
>
> <snip>
>
> Please do not add #ifdef to .c files, that's not the proper kernel
> coding style at all, and just makes maintaining this file much much
> harder over time.
>
> Split things out into two different files if you really need to do this.

What about the static functions that I'll need to turn non-static and
in a header file?
I mean, the functions that the functions in the new file will have to call.
Should I do that, turn static functions into non-static and declared
in a header file?


>
> thanks,
>
> greg k-h



-- 


Daniel Gutson
Engineering Director
Eclypsium, Inc.


Below The Surface: Get the latest threat research and insights on
firmware and supply chain threats from the research team at Eclypsium.
https://eclypsium.com/research/#threatreport