Quelle  jitterentropy-testing.c   Sprache: C

/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
/*
 * Test interface for Jitter RNG.
 *
 * Copyright (C) 2023, Stephan Mueller <smueller@chronox.de>
 */

#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/uaccess.h>

#include "jitterentropy.h"

#define JENT_TEST_RINGBUFFER_SIZE (1<<10)
#define JENT_TEST_RINGBUFFER_MASK (JENT_TEST_RINGBUFFER_SIZE - 1)

struct jent_testing {
 u64 jent_testing_rb[JENT_TEST_RINGBUFFER_SIZE];
 u32 rb_reader;
 atomic_t rb_writer;
 atomic_t jent_testing_enabled;
 spinlock_t lock;
 wait_queue_head_t read_wait;
};

static struct dentry *jent_raw_debugfs_root = NULL;

/*************************** Generic Data Handling ****************************/

/*
 * boot variable:
 * 0 ==> No boot test, gathering of runtime data allowed
 * 1 ==> Boot test enabled and ready for collecting data, gathering runtime
 *  data is disabled
 * 2 ==> Boot test completed and disabled, gathering of runtime data is
 *  disabled
 */

static void jent_testing_reset(struct jent_testing *data)
{
 unsigned long flags;

 spin_lock_irqsave(&data->lock, flags);
 data->rb_reader = 0;
 atomic_set(&data->rb_writer, 0);
 spin_unlock_irqrestore(&data->lock, flags);
}

static void jent_testing_data_init(struct jent_testing *data, u32 boot)
{
 /*
 * The boot time testing implies we have a running test. If the
 * caller wants to clear it, he has to unset the boot_test flag
 * at runtime via sysfs to enable regular runtime testing
 */
 if (boot)
  return;

 jent_testing_reset(data);
 atomic_set(&data->jent_testing_enabled, 1);
 pr_warn("Enabling data collection\n");
}

static void jent_testing_fini(struct jent_testing *data, u32 boot)
{
 /* If we have boot data, we do not reset yet to allow data to be read */
 if (boot)
  return;

 atomic_set(&data->jent_testing_enabled, 0);
 jent_testing_reset(data);
 pr_warn("Disabling data collection\n");
}

static bool jent_testing_store(struct jent_testing *data, u64 value,
          u32 *boot)
{
 unsigned long flags;

 if (!atomic_read(&data->jent_testing_enabled) && (*boot != 1))
  return false;

 spin_lock_irqsave(&data->lock, flags);

 /*
 * Disable entropy testing for boot time testing after ring buffer
 * is filled.
 */
 if (*boot) {
  if (((u32)atomic_read(&data->rb_writer)) >
       JENT_TEST_RINGBUFFER_SIZE) {
   *boot = 2;
   pr_warn_once("One time data collection test disabled\n");
   spin_unlock_irqrestore(&data->lock, flags);
   return false;
  }

  if (atomic_read(&data->rb_writer) == 1)
   pr_warn("One time data collection test enabled\n");
 }

 data->jent_testing_rb[((u32)atomic_read(&data->rb_writer)) &
         JENT_TEST_RINGBUFFER_MASK] = value;
 atomic_inc(&data->rb_writer);

 spin_unlock_irqrestore(&data->lock, flags);

 if (wq_has_sleeper(&data->read_wait))
  wake_up_interruptible(&data->read_wait);

 return true;
}

static bool jent_testing_have_data(struct jent_testing *data)
{
 return ((((u32)atomic_read(&data->rb_writer)) &
   JENT_TEST_RINGBUFFER_MASK) !=
   (data->rb_reader & JENT_TEST_RINGBUFFER_MASK));
}

static int jent_testing_reader(struct jent_testing *data, u32 *boot,
          u8 *outbuf, u32 outbuflen)
{
 unsigned long flags;
 int collected_data = 0;

 jent_testing_data_init(data, *boot);

 while (outbuflen) {
  u32 writer = (u32)atomic_read(&data->rb_writer);

  spin_lock_irqsave(&data->lock, flags);

  /* We have no data or reached the writer. */
  if (!writer || (writer == data->rb_reader)) {

   spin_unlock_irqrestore(&data->lock, flags);

   /*
 * Now we gathered all boot data, enable regular data
 * collection.
 */
   if (*boot) {
    *boot = 0;
    goto out;
   }

   wait_event_interruptible(data->read_wait,
       jent_testing_have_data(data));
   if (signal_pending(current)) {
    collected_data = -ERESTARTSYS;
    goto out;
   }

   continue;
  }

  /* We copy out word-wise */
  if (outbuflen < sizeof(u64)) {
   spin_unlock_irqrestore(&data->lock, flags);
   goto out;
  }

  memcpy(outbuf, &data->jent_testing_rb[data->rb_reader],
         sizeof(u64));
  data->rb_reader++;

  spin_unlock_irqrestore(&data->lock, flags);

  outbuf += sizeof(u64);
  outbuflen -= sizeof(u64);
  collected_data += sizeof(u64);
 }

out:
 jent_testing_fini(data, *boot);
 return collected_data;
}

static int jent_testing_extract_user(struct file *file, char __user *buf,
         size_t nbytes, loff_t *ppos,
         int (*reader)(u8 *outbuf, u32 outbuflen))
{
 u8 *tmp, *tmp_aligned;
 int ret = 0, large_request = (nbytes > 256);

 if (!nbytes)
  return 0;

 /*
 * The intention of this interface is for collecting at least
 * 1000 samples due to the SP800-90B requirements. However, due to
 * memory and performance constraints, it is not desirable to allocate
 * 8000 bytes of memory. Instead, we allocate space for only 125
 * samples, which will allow the user to collect all 1000 samples using
 * 8 calls to this interface.
 */
 tmp = kmalloc(125 * sizeof(u64) + sizeof(u64), GFP_KERNEL);
 if (!tmp)
  return -ENOMEM;

 tmp_aligned = PTR_ALIGN(tmp, sizeof(u64));

 while (nbytes) {
  int i;

  if (large_request && need_resched()) {
   if (signal_pending(current)) {
    if (ret == 0)
     ret = -ERESTARTSYS;
    break;
   }
   schedule();
  }

  i = min_t(int, nbytes, 125 * sizeof(u64));
  i = reader(tmp_aligned, i);
  if (i <= 0) {
   if (i < 0)
    ret = i;
   break;
  }
  if (copy_to_user(buf, tmp_aligned, i)) {
   ret = -EFAULT;
   break;
  }

  nbytes -= i;
  buf += i;
  ret += i;
 }

 kfree_sensitive(tmp);

 if (ret > 0)
  *ppos += ret;

 return ret;
}

/************** Raw High-Resolution Timer Entropy Data Handling **************/

static u32 boot_raw_hires_test = 0;
module_param(boot_raw_hires_test, uint, 0644);
MODULE_PARM_DESC(boot_raw_hires_test,
   "Enable gathering boot time high resolution timer entropy of the first Jitter RNG entropy events");

static struct jent_testing jent_raw_hires = {
 .rb_reader = 0,
 .rb_writer = ATOMIC_INIT(0),
 .lock      = __SPIN_LOCK_UNLOCKED(jent_raw_hires.lock),
 .read_wait = __WAIT_QUEUE_HEAD_INITIALIZER(jent_raw_hires.read_wait)
};

int jent_raw_hires_entropy_store(__u64 value)
{
 return jent_testing_store(&jent_raw_hires, value, &boot_raw_hires_test);
}
EXPORT_SYMBOL(jent_raw_hires_entropy_store);

static int jent_raw_hires_entropy_reader(u8 *outbuf, u32 outbuflen)
{
 return jent_testing_reader(&jent_raw_hires, &boot_raw_hires_test,
       outbuf, outbuflen);
}

static ssize_t jent_raw_hires_read(struct file *file, char __user *to,
       size_t count, loff_t *ppos)
{
 return jent_testing_extract_user(file, to, count, ppos,
      jent_raw_hires_entropy_reader);
}

static const struct file_operations jent_raw_hires_fops = {
 .owner = THIS_MODULE,
 .read = jent_raw_hires_read,
};

/******************************* Initialization *******************************/

void jent_testing_init(void)
{
 jent_raw_debugfs_root = debugfs_create_dir(KBUILD_MODNAME, NULL);

 debugfs_create_file_unsafe("jent_raw_hires", 0400,
       jent_raw_debugfs_root, NULL,
       &jent_raw_hires_fops);
}
EXPORT_SYMBOL(jent_testing_init);

void jent_testing_exit(void)
{
 debugfs_remove_recursive(jent_raw_debugfs_root);
}
EXPORT_SYMBOL(jent_testing_exit);