misc: Add Nitro Secure Module driver

When running Linux inside a Nitro Enclave, the hypervisor provides a
special virtio device called "Nitro Security Module" (NSM). This device
has 3 main functions:

  1) Provide attestation reports
  2) Modify PCR state
  3) Provide entropy

This patch adds a driver for NSM that exposes a /dev/nsm device node which
user space can issue an ioctl on this device with raw NSM CBOR formatted
commands to request attestation documents, influence PCR states, read
entropy and enumerate status of the device. In addition, the driver
implements a hwrng backend.

Originally-by: Petre Eftime <petre.eftime@gmail.com>
Signed-off-by: Alexander Graf <graf@amazon.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20231011213522.51781-1-graf@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -15291,6 +15291,15 @@ F:	include/linux/nitro_enclaves.h
 F:	include/uapi/linux/nitro_enclaves.h
 F:	samples/nitro_enclaves/
 
+NITRO SECURE MODULE (NSM)
+M:	Alexander Graf <graf@amazon.com>
+L:	linux-kernel@vger.kernel.org
+L:	The AWS Nitro Enclaves Team <aws-nitro-enclaves-devel@amazon.com>
+S:	Supported
+W:	https://aws.amazon.com/ec2/nitro/nitro-enclaves/
+F:	drivers/misc/nsm.c
+F:	include/uapi/linux/nsm.h
+
 NOHZ, DYNTICKS SUPPORT
 M:	Frederic Weisbecker <frederic@kernel.org>
 M:	Thomas Gleixner <tglx@linutronix.de>

drivers/misc/Kconfig

@@ -562,6 +562,19 @@ config TPS6594_PFSM
 	  This driver can also be built as a module.  If so, the module
 	  will be called tps6594-pfsm.
 
+config NSM
+	tristate "Nitro (Enclaves) Security Module support"
+	depends on VIRTIO
+	select HW_RANDOM
+	select CBOR
+	help
+	  This driver provides support for the Nitro Security Module
+	  in AWS EC2 Nitro based Enclaves. The driver exposes a /dev/nsm
+	  device user space can use to communicate with the hypervisor.
+
+	  To compile this driver as a module, choose M here.
+	  The module will be called nsm.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"

drivers/misc/Makefile

@@ -67,3 +67,4 @@ obj-$(CONFIG_TMR_MANAGER)      += xilinx_tmr_manager.o
 obj-$(CONFIG_TMR_INJECT)	+= xilinx_tmr_inject.o
 obj-$(CONFIG_TPS6594_ESM)	+= tps6594-esm.o
 obj-$(CONFIG_TPS6594_PFSM)	+= tps6594-pfsm.o
+obj-$(CONFIG_NSM)		+= nsm.o