[v2] um: Rewrite host RNG driver.
diff mbox series

Message ID 20190829135001.6a5ff940@TheDarkness.local
State Rejected
Headers show
Series
  • [v2] um: Rewrite host RNG driver.
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Commit Message

Alexander Neville Aug. 29, 2019, 5:56 p.m. UTC
The old driver had a bug that would cause it to outright stop working if
the host's /dev/random were to block. Instead of trying to track down
the cause of said bug, rewriting it from scratch turned out to be a much
better option as it came with a few benefits:

 - The new driver uses the hw_random framework.

 - The code is simpler and therefore easier to maintain.

 - It serves as a minimal example of writing a hardware RNG driver.

I also edited the Kconfig symbol to bring it up to more modern
standards.

Signed-off-by: Alexander Neville <dark@volatile.bz>
---
v2:
* fix -EAGAIN handling

---
 arch/um/drivers/Makefile       |   3 +-
 arch/um/drivers/random.c       | 199 +++++++++------------------------
 drivers/char/hw_random/Kconfig |  21 ++--
 3 files changed, 66 insertions(+), 157 deletions(-)

Comments

Richard Weinberger Aug. 29, 2019, 6:48 p.m. UTC | #1
----- Ursprüngliche Mail -----
> Von: "Dark" <dark@volatile.bz>
> +	// Returning -EAGAIN to userspace is not nice.
> +	if (err == -EAGAIN)
> +		return 0;

Hmm, doesn't this result in a short read?
The current drives sets the calling task to sleep and wakes
it up as soon data is available again. I'd assumes ti have the
same behavior for the new driver.

Thanks,
//richard
Alexander Neville Aug. 29, 2019, 8:56 p.m. UTC | #2
On Thu, 29 Aug 2019 20:48:33 +0200 (CEST), Richard Weinberger <richard@nod.at> wrote:

> ----- Ursprüngliche Mail -----
> > Von: "Dark" <dark@volatile.bz>
> > +	// Returning -EAGAIN to userspace is not nice.
> > +	if (err == -EAGAIN)
> > +		return 0;  
> 
> Hmm, doesn't this result in a short read?
> The current drives sets the calling task to sleep and wakes
> it up as soon data is available again. I'd assumes ti have the
> same behavior for the new driver.
> 
> Thanks,
> //richard

Clearly this patch needs a lot more work before I submit it. I'll 
take some time to polish it up and then resubmit it if that's fine.
Richard Weinberger Aug. 29, 2019, 9:03 p.m. UTC | #3
----- Ursprüngliche Mail -----
>> ----- Ursprüngliche Mail -----
>> > Von: "Dark" <dark@volatile.bz>
>> > +	// Returning -EAGAIN to userspace is not nice.
>> > +	if (err == -EAGAIN)
>> > +		return 0;
>> 
>> Hmm, doesn't this result in a short read?
>> The current drives sets the calling task to sleep and wakes
>> it up as soon data is available again. I'd assumes ti have the
>> same behavior for the new driver.
>> 
>> Thanks,
>> //richard
> 
> Clearly this patch needs a lot more work before I submit it. I'll
> take some time to polish it up and then resubmit it if that's fine.

No need to worry, take your time. Thanks a lot for working on this driver!

Thanks,
//richard

Patch
diff mbox series

diff --git a/arch/um/drivers/Makefile b/arch/um/drivers/Makefile
index 693319839f69..29b0364f267d 100644
--- a/arch/um/drivers/Makefile
+++ b/arch/um/drivers/Makefile
@@ -17,6 +17,7 @@  hostaudio-objs := hostaudio_kern.o
 ubd-objs := ubd_kern.o ubd_user.o
 port-objs := port_kern.o port_user.o
 harddog-objs := harddog_kern.o harddog_user.o
+uml-rng-objs := random.o
 
 LDFLAGS_pcap.o := -r $(shell $(CC) $(KBUILD_CFLAGS) -print-file-name=libpcap.a)
 
@@ -60,7 +61,7 @@  obj-$(CONFIG_TTY_CHAN) += tty.o
 obj-$(CONFIG_XTERM_CHAN) += xterm.o xterm_kern.o
 obj-$(CONFIG_UML_WATCHDOG) += harddog.o
 obj-$(CONFIG_BLK_DEV_COW_COMMON) += cow_user.o
-obj-$(CONFIG_UML_RANDOM) += random.o
+obj-$(CONFIG_UML_RANDOM) += uml-rng.o
 
 # pcap_user.o must be added explicitly.
 USER_OBJS := fd.o null.o pty.o tty.o xterm.o slip_common.o pcap_user.o vde_user.o vector_user.o
diff --git a/arch/um/drivers/random.c b/arch/um/drivers/random.c
index 1d5d3057e6f1..cb8eb026df9c 100644
--- a/arch/um/drivers/random.c
+++ b/arch/um/drivers/random.c
@@ -1,175 +1,82 @@ 
-/* Copyright (C) 2005 - 2008 Jeff Dike <jdike@{linux.intel,addtoit}.com> */
-
-/* Much of this ripped from drivers/char/hw_random.c, see there for other
- * copyright.
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * UML Host RNG Driver
+ *
+ * (c) Copright 2019 Alexander Neville <dark@volatile.bz>
  *
- * This software may be used and distributed according to the terms
- * of the GNU General Public License, incorporated herein by reference.
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
  */
-#include <linux/sched/signal.h>
+
+#include <linux/errno.h>
+#include <linux/fcntl.h>
+#include <linux/hw_random.h>
+#include <linux/kernel.h>
 #include <linux/module.h>
-#include <linux/fs.h>
-#include <linux/interrupt.h>
-#include <linux/miscdevice.h>
-#include <linux/delay.h>
-#include <linux/uaccess.h>
-#include <init.h>
-#include <irq_kern.h>
+#include <linux/types.h>
 #include <os.h>
 
-/*
- * core module and version information
- */
-#define RNG_VERSION "1.0.0"
-#define RNG_MODULE_NAME "hw_random"
-
-#define RNG_MISCDEV_MINOR		183 /* official */
-
-/* Changed at init time, in the non-modular case, and at module load
- * time, in the module case.  Presumably, the module subsystem
- * protects against a module being loaded twice at the same time.
- */
-static int random_fd = -1;
-static DECLARE_WAIT_QUEUE_HEAD(host_read_wait);
-
-static int rng_dev_open (struct inode *inode, struct file *filp)
+static int uml_rng_read(struct hwrng *rng, void *data, size_t bufsize,
+			bool wait)
 {
-	/* enforce read-only access to this chrdev */
-	if ((filp->f_mode & FMODE_READ) == 0)
-		return -EINVAL;
-	if ((filp->f_mode & FMODE_WRITE) != 0)
-		return -EINVAL;
+	int err = os_read_file(rng->priv, data, bufsize);
 
-	return 0;
-}
+	// Returning -EAGAIN to userspace is not nice.
+	if (err == -EAGAIN)
+		return 0;
 
-static atomic_t host_sleep_count = ATOMIC_INIT(0);
+	return err;
+}
 
-static ssize_t rng_dev_read (struct file *filp, char __user *buf, size_t size,
-			     loff_t *offp)
+static int uml_rng_init(struct hwrng *rng)
 {
-	u32 data;
-	int n, ret = 0, have_data;
-
-	while (size) {
-		n = os_read_file(random_fd, &data, sizeof(data));
-		if (n > 0) {
-			have_data = n;
-			while (have_data && size) {
-				if (put_user((u8) data, buf++)) {
-					ret = ret ? : -EFAULT;
-					break;
-				}
-				size--;
-				ret++;
-				have_data--;
-				data >>= 8;
-			}
-		}
-		else if (n == -EAGAIN) {
-			DECLARE_WAITQUEUE(wait, current);
-
-			if (filp->f_flags & O_NONBLOCK)
-				return ret ? : -EAGAIN;
-
-			atomic_inc(&host_sleep_count);
-			add_sigio_fd(random_fd);
-
-			add_wait_queue(&host_read_wait, &wait);
-			set_current_state(TASK_INTERRUPTIBLE);
-
-			schedule();
-			remove_wait_queue(&host_read_wait, &wait);
-
-			if (atomic_dec_and_test(&host_sleep_count)) {
-				ignore_sigio_fd(random_fd);
-				deactivate_fd(random_fd, RANDOM_IRQ);
-			}
-		}
-		else
-			return n;
-
-		if (signal_pending (current))
-			return ret ? : -ERESTARTSYS;
+	int fd = os_open_file("/dev/random", of_read(OPENFLAGS()), O_NONBLOCK);
+
+	if (fd < 0) {
+		pr_debug("uml-rng: failed to open /dev/random");
+		return fd;
 	}
-	return ret;
-}
 
-static const struct file_operations rng_chrdev_ops = {
-	.owner		= THIS_MODULE,
-	.open		= rng_dev_open,
-	.read		= rng_dev_read,
-	.llseek		= noop_llseek,
-};
+	int err = os_set_fd_async(fd);
 
-/* rng_init shouldn't be called more than once at boot time */
-static struct miscdevice rng_miscdev = {
-	RNG_MISCDEV_MINOR,
-	RNG_MODULE_NAME,
-	&rng_chrdev_ops,
-};
+	if (err < 0) {
+		os_close_file(fd);
+		return err;
+	}
 
-static irqreturn_t random_interrupt(int irq, void *data)
-{
-	wake_up(&host_read_wait);
+	rng->priv = fd;
 
-	return IRQ_HANDLED;
+	return 0;
 }
 
-/*
- * rng_init - initialize RNG module
- */
-static int __init rng_init (void)
+static void uml_rng_cleanup(struct hwrng *rng)
 {
-	int err;
-
-	err = os_open_file("/dev/random", of_read(OPENFLAGS()), 0);
-	if (err < 0)
-		goto out;
-
-	random_fd = err;
-
-	err = um_request_irq(RANDOM_IRQ, random_fd, IRQ_READ, random_interrupt,
-			     0, "random", NULL);
-	if (err)
-		goto err_out_cleanup_hw;
-
-	sigio_broken(random_fd, 1);
-
-	err = misc_register (&rng_miscdev);
-	if (err) {
-		printk (KERN_ERR RNG_MODULE_NAME ": misc device register "
-			"failed\n");
-		goto err_out_cleanup_hw;
-	}
-out:
-	return err;
-
-err_out_cleanup_hw:
-	os_close_file(random_fd);
-	random_fd = -1;
-	goto out;
+	os_close_file(rng->priv);
 }
 
-/*
- * rng_cleanup - shutdown RNG module
- */
 
-static void cleanup(void)
+static struct hwrng uml_rng_ops = {
+	.name		= "uml-rng",
+	.init		= uml_rng_init,
+	.cleanup	= uml_rng_cleanup,
+	.read		= uml_rng_read,
+	.quality	= 1024
+};
+
+static int __init uml_rng_mod_init(void)
 {
-	free_irq_by_fd(random_fd);
-	os_close_file(random_fd);
+	return hwrng_register(&uml_rng_ops);
 }
 
-static void __exit rng_cleanup(void)
+static void __exit uml_rng_mod_exit(void)
 {
-	os_close_file(random_fd);
-	misc_deregister (&rng_miscdev);
+	hwrng_unregister(&uml_rng_ops);
 }
 
-module_init (rng_init);
-module_exit (rng_cleanup);
-__uml_exitcall(cleanup);
+module_init(uml_rng_mod_init);
+module_exit(uml_rng_mod_exit);
 
-MODULE_DESCRIPTION("UML Host Random Number Generator (RNG) driver");
+MODULE_AUTHOR("Alexander Neville <dark@volatile.bz>");
+MODULE_DESCRIPTION("UML Host RNG Driver");
 MODULE_LICENSE("GPL");
diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index 59f25286befe..a0781f74d4e4 100644
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -440,22 +440,23 @@  config HW_RANDOM_OPTEE
 
 	  If unsure, say Y.
 
-endif # HW_RANDOM
-
 config UML_RANDOM
+	tristate "UML Host Random Number Generator Support"
 	depends on UML
-	tristate "Hardware random number generator"
+	default HW_RANDOM
 	help
 	  This option enables UML's "hardware" random number generator.  It
 	  attaches itself to the host's /dev/random, supplying as much entropy
 	  as the host has, rather than the small amount the UML gets from its
-	  own drivers.  It registers itself as a standard hardware random number
-	  generator, major 10, minor 183, and the canonical device name is
-	  /dev/hwrng.
-	  The way to make use of this is to install the rng-tools package
-	  (check your distro, or download from
-	  http://sourceforge.net/projects/gkernel/).  rngd periodically reads
-	  /dev/hwrng and injects the entropy into /dev/random.
+	  own drivers.
+
+	  To compile this driver as a moudle, choose M here: the module
+	  will be called uml-rng.
+
+	  If unsure, say Y.
+
+endif # HW_RANDOM
+
 
 config HW_RANDOM_KEYSTONE
 	depends on ARCH_KEYSTONE