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linux/drivers/char/Kconfig
Jason A. Donenfeld 9592eef7c1 random: remove CONFIG_ARCH_RANDOM 
When RDRAND was introduced, there was much discussion on whether it
should be trusted and how the kernel should handle that. Initially, two
mechanisms cropped up, CONFIG_ARCH_RANDOM, a compile time switch, and
"nordrand", a boot-time switch.

Later the thinking evolved. With a properly designed RNG, using RDRAND
values alone won't harm anything, even if the outputs are malicious.
Rather, the issue is whether those values are being *trusted* to be good
or not. And so a new set of options were introduced as the real
ones that people use -- CONFIG_RANDOM_TRUST_CPU and "random.trust_cpu".
With these options, RDRAND is used, but it's not always credited. So in
the worst case, it does nothing, and in the best case, maybe it helps.

Along the way, CONFIG_ARCH_RANDOM's meaning got sort of pulled into the
center and became something certain platforms force-select.

The old options don't really help with much, and it's a bit odd to have
special handling for these instructions when the kernel can deal fine
with the existence or untrusted existence or broken existence or
non-existence of that CPU capability.

Simplify the situation by removing CONFIG_ARCH_RANDOM and using the
ordinary asm-generic fallback pattern instead, keeping the two options
that are actually used. For now it leaves "nordrand" for now, as the
removal of that will take a different route.

Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
2022-07-18 15:03:37 +02:00

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# SPDX-License-Identifier: GPL-2.0
#
# Character device configuration
#
menu "Character devices"
source "drivers/tty/Kconfig"
config TTY_PRINTK
tristate "TTY driver to output user messages via printk"
depends on EXPERT && TTY
default n
help
If you say Y here, the support for writing user messages (i.e.
console messages) via printk is available.
The feature is useful to inline user messages with kernel
messages.
In order to use this feature, you should output user messages
to /dev/ttyprintk or redirect console to this TTY, or boot
the kernel with console=ttyprintk.
If unsure, say N.
config TTY_PRINTK_LEVEL
depends on TTY_PRINTK
int "ttyprintk log level (1-7)"
range 1 7
default "6"
help
Printk log level to use for ttyprintk messages.
config PRINTER
tristate "Parallel printer support"
depends on PARPORT
help
If you intend to attach a printer to the parallel port of your Linux
box (as opposed to using a serial printer; if the connector at the
printer has 9 or 25 holes ["female"], then it's serial), say Y.
Also read the Printing-HOWTO, available from
<https://www.tldp.org/docs.html#howto>.
It is possible to share one parallel port among several devices
(e.g. printer and ZIP drive) and it is safe to compile the
corresponding drivers into the kernel.
To compile this driver as a module, choose M here and read
<file:Documentation/admin-guide/parport.rst>. The module will be called lp.
If you have several parallel ports, you can specify which ports to
use with the "lp" kernel command line option. (Try "man bootparam"
or see the documentation of your boot loader (lilo or loadlin) about
how to pass options to the kernel at boot time.) The syntax of the
"lp" command line option can be found in <file:drivers/char/lp.c>.
If you have more than 8 printers, you need to increase the LP_NO
macro in lp.c and the PARPORT_MAX macro in parport.h.
config LP_CONSOLE
bool "Support for console on line printer"
depends on PRINTER
help
If you want kernel messages to be printed out as they occur, you
can have a console on the printer. This option adds support for
doing that; to actually get it to happen you need to pass the
option "console=lp0" to the kernel at boot time.
If the printer is out of paper (or off, or unplugged, or too
busy..) the kernel will stall until the printer is ready again.
By defining CONSOLE_LP_STRICT to 0 (at your own risk) you
can make the kernel continue when this happens,
but it'll lose the kernel messages.
If unsure, say N.
config PPDEV
tristate "Support for user-space parallel port device drivers"
depends on PARPORT
help
Saying Y to this adds support for /dev/parport device nodes. This
is needed for programs that want portable access to the parallel
port, for instance deviceid (which displays Plug-and-Play device
IDs).
This is the parallel port equivalent of SCSI generic support (sg).
It is safe to say N to this -- it is not needed for normal printing
or parallel port CD-ROM/disk support.
To compile this driver as a module, choose M here: the
module will be called ppdev.
If unsure, say N.
config VIRTIO_CONSOLE
tristate "Virtio console"
depends on TTY
select HVC_DRIVER
select VIRTIO
help
Virtio console for use with hypervisors.
Also serves as a general-purpose serial device for data
transfer between the guest and host. Character devices at
/dev/vportNpn will be created when corresponding ports are
found, where N is the device number and n is the port number
within that device. If specified by the host, a sysfs
attribute called 'name' will be populated with a name for
the port which can be used by udev scripts to create a
symlink to the device.
config IBM_BSR
tristate "IBM POWER Barrier Synchronization Register support"
depends on PPC_PSERIES
help
This devices exposes a hardware mechanism for fast synchronization
of threads across a large system which avoids bouncing a cacheline
between several cores on a system
config POWERNV_OP_PANEL
tristate "IBM POWERNV Operator Panel Display support"
depends on PPC_POWERNV
default m
help
If you say Y here, a special character device node, /dev/op_panel,
will be created which exposes the operator panel display on IBM
Power Systems machines with FSPs.
If you don't require access to the operator panel display from user
space, say N.
If unsure, say M here to build it as a module called powernv-op-panel.
source "drivers/char/ipmi/Kconfig"
config DS1620
tristate "NetWinder thermometer support"
depends on ARCH_NETWINDER
help
Say Y here to include support for the thermal management hardware
found in the NetWinder. This driver allows the user to control the
temperature set points and to read the current temperature.
It is also possible to say M here to build it as a module (ds1620)
It is recommended to be used on a NetWinder, but it is not a
necessity.
config NWBUTTON
tristate "NetWinder Button"
depends on ARCH_NETWINDER
help
If you say Y here and create a character device node /dev/nwbutton
with major and minor numbers 10 and 158 ("man mknod"), then every
time the orange button is pressed a number of times, the number of
times the button was pressed will be written to that device.
This is most useful for applications, as yet unwritten, which
perform actions based on how many times the button is pressed in a
row.
Do not hold the button down for too long, as the driver does not
alter the behaviour of the hardware reset circuitry attached to the
button; it will still execute a hard reset if the button is held
down for longer than approximately five seconds.
To compile this driver as a module, choose M here: the
module will be called nwbutton.
Most people will answer Y to this question and "Reboot Using Button"
below to be able to initiate a system shutdown from the button.
config NWBUTTON_REBOOT
bool "Reboot Using Button"
depends on NWBUTTON
help
If you say Y here, then you will be able to initiate a system
shutdown and reboot by pressing the orange button a number of times.
The number of presses to initiate the shutdown is two by default,
but this can be altered by modifying the value of NUM_PRESSES_REBOOT
in nwbutton.h and recompiling the driver or, if you compile the
driver as a module, you can specify the number of presses at load
time with "insmod button reboot_count=<something>".
config NWFLASH
tristate "NetWinder flash support"
depends on ARCH_NETWINDER
help
If you say Y here and create a character device /dev/flash with
major 10 and minor 160 you can manipulate the flash ROM containing
the NetWinder firmware. Be careful as accidentally overwriting the
flash contents can render your computer unbootable. On no account
allow random users access to this device. :-)
To compile this driver as a module, choose M here: the
module will be called nwflash.
If you're not sure, say N.
source "drivers/char/hw_random/Kconfig"
config DTLK
tristate "Double Talk PC internal speech card support"
depends on ISA
help
This driver is for the DoubleTalk PC, a speech synthesizer
manufactured by RC Systems (<https://www.rcsys.com/>). It is also
called the `internal DoubleTalk'.
To compile this driver as a module, choose M here: the
module will be called dtlk.
config XILINX_HWICAP
tristate "Xilinx HWICAP Support"
depends on MICROBLAZE
help
This option enables support for Xilinx Internal Configuration
Access Port (ICAP) driver. The ICAP is used on Xilinx Virtex
FPGA platforms to partially reconfigure the FPGA at runtime.
If unsure, say N.
config APPLICOM
tristate "Applicom intelligent fieldbus card support"
depends on PCI
help
This driver provides the kernel-side support for the intelligent
fieldbus cards made by Applicom International. More information
about these cards can be found on the WWW at the address
<https://www.applicom-int.com/>, or by email from David Woodhouse
<dwmw2@infradead.org>.
To compile this driver as a module, choose M here: the
module will be called applicom.
If unsure, say N.
config SONYPI
tristate "Sony Vaio Programmable I/O Control Device support"
depends on X86_32 && PCI && INPUT
help
This driver enables access to the Sony Programmable I/O Control
Device which can be found in many (all ?) Sony Vaio laptops.
If you have one of those laptops, read
<file:Documentation/admin-guide/laptops/sonypi.rst>, and say Y or M here.
To compile this driver as a module, choose M here: the
module will be called sonypi.
config GPIO_TB0219
tristate "TANBAC TB0219 GPIO support"
depends on TANBAC_TB022X
select GPIO_VR41XX
source "drivers/char/pcmcia/Kconfig"
config MWAVE
tristate "ACP Modem (Mwave) support"
depends on X86 && TTY
select SERIAL_8250
help
The ACP modem (Mwave) for Linux is a WinModem. It is composed of a
kernel driver and a user level application. Together these components
support direct attachment to public switched telephone networks (PSTNs)
and support selected world wide countries.
This version of the ACP Modem driver supports the IBM Thinkpad 600E,
600, and 770 that include on board ACP modem hardware.
The modem also supports the standard communications port interface
(ttySx) and is compatible with the Hayes AT Command Set.
The user level application needed to use this driver can be found at
the IBM Linux Technology Center (LTC) web site:
<http://www.ibm.com/linux/ltc/>.
If you own one of the above IBM Thinkpads which has the Mwave chipset
in it, say Y.
To compile this driver as a module, choose M here: the
module will be called mwave.
config SCx200_GPIO
tristate "NatSemi SCx200 GPIO Support"
depends on SCx200
select NSC_GPIO
help
Give userspace access to the GPIO pins on the National
Semiconductor SCx200 processors.
If compiled as a module, it will be called scx200_gpio.
config PC8736x_GPIO
tristate "NatSemi PC8736x GPIO Support"
depends on X86_32 && !UML
default SCx200_GPIO # mostly N
select NSC_GPIO # needed for support routines
help
Give userspace access to the GPIO pins on the National
Semiconductor PC-8736x (x=[03456]) SuperIO chip. The chip
has multiple functional units, inc several managed by
hwmon/pc87360 driver. Tested with PC-87366
If compiled as a module, it will be called pc8736x_gpio.
config NSC_GPIO
tristate "NatSemi Base GPIO Support"
depends on X86_32
# selected by SCx200_GPIO and PC8736x_GPIO
# what about 2 selectors differing: m != y
help
Common support used (and needed) by scx200_gpio and
pc8736x_gpio drivers. If those drivers are built as
modules, this one will be too, named nsc_gpio
config DEVMEM
bool "/dev/mem virtual device support"
default y
help
Say Y here if you want to support the /dev/mem device.
The /dev/mem device is used to access areas of physical
memory.
When in doubt, say "Y".
config NVRAM
tristate "/dev/nvram support"
depends on X86 || HAVE_ARCH_NVRAM_OPS
default M68K || PPC
help
If you say Y here and create a character special file /dev/nvram
with major number 10 and minor number 144 using mknod ("man mknod"),
you get read and write access to the non-volatile memory.
/dev/nvram may be used to view settings in NVRAM or to change them
(with some utility). It could also be used to frequently
save a few bits of very important data that may not be lost over
power-off and for which writing to disk is too insecure. Note
however that most NVRAM space in a PC belongs to the BIOS and you
should NEVER idly tamper with it. See Ralf Brown's interrupt list
for a guide to the use of CMOS bytes by your BIOS.
This memory is conventionally called "NVRAM" on PowerPC machines,
"CMOS RAM" on PCs, "NVRAM" on Ataris and "PRAM" on Macintoshes.
To compile this driver as a module, choose M here: the
module will be called nvram.
config DEVPORT
bool "/dev/port character device"
depends on ISA || PCI
default y
help
Say Y here if you want to support the /dev/port device. The /dev/port
device is similar to /dev/mem, but for I/O ports.
config HPET
bool "HPET - High Precision Event Timer" if (X86 || IA64)
default n
depends on ACPI
help
If you say Y here, you will have a miscdevice named "/dev/hpet/". Each
open selects one of the timers supported by the HPET. The timers are
non-periodic and/or periodic.
config HPET_MMAP
bool "Allow mmap of HPET"
default y
depends on HPET
help
If you say Y here, user applications will be able to mmap
the HPET registers.
config HPET_MMAP_DEFAULT
bool "Enable HPET MMAP access by default"
default y
depends on HPET_MMAP
help
In some hardware implementations, the page containing HPET
registers may also contain other things that shouldn't be
exposed to the user. This option selects the default (if
kernel parameter hpet_mmap is not set) user access to the
registers for applications that require it.
config HANGCHECK_TIMER
tristate "Hangcheck timer"
depends on X86 || IA64 || PPC64 || S390
help
The hangcheck-timer module detects when the system has gone
out to lunch past a certain margin. It can reboot the system
or merely print a warning.
config UV_MMTIMER
tristate "UV_MMTIMER Memory mapped RTC for SGI UV"
depends on X86_UV
default m
help
The uv_mmtimer device allows direct userspace access to the
UV system timer.
source "drivers/char/tpm/Kconfig"
config TELCLOCK
tristate "Telecom clock driver for ATCA SBC"
depends on X86
default n
help
The telecom clock device is specific to the MPCBL0010 and MPCBL0050
ATCA computers and allows direct userspace access to the
configuration of the telecom clock configuration settings. This
device is used for hardware synchronization across the ATCA backplane
fabric. Upon loading, the driver exports a sysfs directory,
/sys/devices/platform/telco_clock, with a number of files for
controlling the behavior of this hardware.
source "drivers/s390/char/Kconfig"
source "drivers/char/xillybus/Kconfig"
config ADI
tristate "SPARC Privileged ADI driver"
depends on SPARC64
default m
help
SPARC M7 and newer processors utilize ADI (Application Data
Integrity) to version and protect memory. This driver provides
read/write access to the ADI versions for privileged processes.
This feature is also known as MCD (Memory Corruption Detection)
and SSM (Silicon Secured Memory). Intended consumers of this
driver include crash and makedumpfile.
config RANDOM_TRUST_CPU
bool "Initialize RNG using CPU RNG instructions"
default y
help
Initialize the RNG using random numbers supplied by the CPU's
RNG instructions (e.g. RDRAND), if supported and available. These
random numbers are never used directly, but are rather hashed into
the main input pool, and this happens regardless of whether or not
this option is enabled. Instead, this option controls whether the
they are credited and hence can initialize the RNG. Additionally,
other sources of randomness are always used, regardless of this
setting. Enabling this implies trusting that the CPU can supply high
quality and non-backdoored random numbers.
Say Y here unless you have reason to mistrust your CPU or believe
its RNG facilities may be faulty. This may also be configured at
boot time with "random.trust_cpu=on/off".
config RANDOM_TRUST_BOOTLOADER
bool "Initialize RNG using bootloader-supplied seed"
default y
help
Initialize the RNG using a seed supplied by the bootloader or boot
environment (e.g. EFI or a bootloader-generated device tree). This
seed is not used directly, but is rather hashed into the main input
pool, and this happens regardless of whether or not this option is
enabled. Instead, this option controls whether the seed is credited
and hence can initialize the RNG. Additionally, other sources of
randomness are always used, regardless of this setting. Enabling
this implies trusting that the bootloader can supply high quality and
non-backdoored seeds.
Say Y here unless you have reason to mistrust your bootloader or
believe its RNG facilities may be faulty. This may also be configured
at boot time with "random.trust_bootloader=on/off".
endmenu
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