Add entropy pool and strong random number generator

Entropy pool gathers environmental noise from device drivers, user-space, etc., and returns good random numbers, suitable for cryptographic use. Based on entropy pool design from *BSDs and uses BLAKE2Xs algorithm for CSPRNG output.

Patch also adds /dev/urandom support for using entropy pool RNG and new 'getrandom' system call for getting randomness without file-descriptor usage (thus avoiding file-descriptor exhaustion attacks). The 'getrandom' interface is similar as 'getentropy' and 'getrandom' available on OpenBSD and Linux respectively.

drivers/input/ads7843e.c

@@ -70,6 +70,7 @@
 #include <nuttx/fs/fs.h>
 #include <nuttx/spi/spi.h>
 #include <nuttx/wqueue.h>
+#include <nuttx/random.h>
 
 #include <nuttx/semaphore.h>
 #include <nuttx/input/touchscreen.h>
@@ -624,6 +625,8 @@ static void ads7843e_worker(FAR void *arg)
       y = ads7843e_sendcmd(priv, ADS7843_CMD_YPOSITION);
 #endif
 
+      add_ui_randomness((x << 16) | y);
+
       /* Perform a thresholding operation so that the results will be more stable.
        * If the difference from the last sample is small, then ignore the event.
        * REVISIT:  Should a large change in pressure also generate a event?

drivers/input/ajoystick.c

@@ -60,6 +60,7 @@
 #include <nuttx/kmalloc.h>
 #include <nuttx/fs/fs.h>
 #include <nuttx/input/ajoystick.h>
+#include <nuttx/random.h>
 
 #include <nuttx/irq.h>
 
@@ -321,6 +322,8 @@ static void ajoy_sample(FAR struct ajoy_upperhalf_s *priv)
   DEBUGASSERT(lower->al_buttons);
   sample = lower->al_buttons(lower);
 
+  add_ui_randomness(sample);
+
 #if !defined(CONFIG_DISABLE_POLL) || !defined(CONFIG_DISABLE_SIGNALS)
   /* Determine which buttons have been newly pressed and which have been
    * newly released.

drivers/input/button_upper.c

@@ -56,6 +56,7 @@
 #include <nuttx/kmalloc.h>
 #include <nuttx/fs/fs.h>
 #include <nuttx/input/buttons.h>
+#include <nuttx/random.h>
 
 #include <nuttx/irq.h>
 
@@ -317,6 +318,8 @@ static void btn_sample(FAR struct btn_upperhalf_s *priv)
   DEBUGASSERT(lower->bl_buttons);
   sample = lower->bl_buttons(lower);
 
+  add_ui_randomness(sample);
+
 #if !defined(CONFIG_DISABLE_POLL) || !defined(CONFIG_DISABLE_SIGNALS)
   /* Determine which buttons have been newly pressed and which have been
    * newly released.

drivers/input/djoystick.c

@@ -60,6 +60,7 @@
 #include <nuttx/kmalloc.h>
 #include <nuttx/fs/fs.h>
 #include <nuttx/input/djoystick.h>
+#include <nuttx/random.h>
 
 #include <nuttx/irq.h>
 
@@ -321,6 +322,8 @@ static void djoy_sample(FAR struct djoy_upperhalf_s *priv)
   DEBUGASSERT(lower->dl_sample);
   sample = lower->dl_sample(lower);
 
+  add_ui_randomness(sample);
+
 #if !defined(CONFIG_DISABLE_POLL) || !defined(CONFIG_DISABLE_SIGNALS)
   /* Determine which buttons have been newly pressed and which have been
    * newly released.

drivers/input/max11802.c

@@ -64,6 +64,7 @@
 #include <nuttx/wqueue.h>
 #include <nuttx/fs/fs.h>
 #include <nuttx/spi/spi.h>
+#include <nuttx/random.h>
 
 #include <nuttx/semaphore.h>
 #include <nuttx/input/touchscreen.h>
@@ -628,6 +629,8 @@ static void max11802_worker(FAR void *arg)
         }
       while (readycount < 2);
 
+      add_ui_randomness((x << 16) | y);
+
       /* Continue to sample the position while the pen is down */
 
       wd_start(priv->wdog, MAX11802_WDOG_DELAY, max11802_wdog, 1,

drivers/input/mxt.c

@@ -64,6 +64,7 @@
 #include <nuttx/fs/fs.h>
 #include <nuttx/i2c/i2c_master.h>
 #include <nuttx/wqueue.h>
+#include <nuttx/random.h>
 
 #include <nuttx/semaphore.h>
 #include <nuttx/input/touchscreen.h>
@@ -889,6 +890,8 @@ static void mxt_touch_event(FAR struct mxt_dev_s *priv,
       sample->pressure = pressure;
       sample->valid    = true;
 
+      add_ui_randomness((x << 16) ^ y ^ (area << 9) ^ (pressure << 1));
+
       /* If this is not the first touch report, then report it as a move:
        * Same contact, same ID, but with a new, updated position.
        * The CONTACT_REPORT state means that a contacted has been detected,

drivers/input/stmpe811_temp.c

@@ -48,6 +48,7 @@
 #include <debug.h>
 
 #include <nuttx/input/stmpe811.h>
+#include <nuttx/random.h>
 
 #include "stmpe811.h"
 
@@ -139,6 +140,8 @@ uint16_t stmpe811_tempread(STMPE811_HANDLE handle)
   temp1 = stmpe811_getreg8(priv, STMPE811_SYS_CTRL2);
   temp2 = stmpe811_getreg8(priv, STMPE811_SYS_CTRL2+1);
 
+  add_sensor_randomness((temp1 << 8) | temp2);
+
   /* Scale the temperature (where Vio is assumed to be .33) */
 
   temp = ((uint32_t)(temp1 & 3) << 8) | temp2;

drivers/input/stmpe811_tsc.c

@@ -62,6 +62,7 @@
 #include <nuttx/fs/fs.h>
 #include <nuttx/i2c/i2c_master.h>
 #include <nuttx/wqueue.h>
+#include <nuttx/random.h>
 
 #include <nuttx/arch.h>
 #include <nuttx/input/touchscreen.h>
@@ -534,6 +535,8 @@ static ssize_t stmpe811_read(FAR struct file *filep, FAR char *buffer, size_t le
   report->point[0].y         = sample.y;
   report->point[0].pressure  = sample.z;
 
+  add_ui_randomness((sample.x << 16) ^ (sample.y << 8) ^ sample.z);
+
   /* Report the appropriate flags */
 
   if (sample.contact == CONTACT_UP)

drivers/input/tsc2007.c

@@ -68,6 +68,7 @@
 #include <nuttx/fs/fs.h>
 #include <nuttx/i2c/i2c_master.h>
 #include <nuttx/wqueue.h>
+#include <nuttx/random.h>
 
 #include <nuttx/input/touchscreen.h>
 #include <nuttx/input/tsc2007.h>
@@ -619,7 +620,7 @@ static void tsc2007_worker(FAR void *arg)
        *  vertical or horizontal resistive network.  The A/D converter converts
        *  the voltage measured at the point where the panel is touched. A measurement
        *  of the Y position of the pointing device is made by connecting the X+
-       *  input to a data converter chip, turning on the Y+ and Y– drivers, and
+       *  input to a data converter chip, turning on the Y+ and Y- drivers, and
        *  digitizing the voltage seen at the X+ input ..."
        *
        * "... it is recommended that whenever the host writes to the TSC2007, the
@@ -698,6 +699,8 @@ static void tsc2007_worker(FAR void *arg)
       priv->sample.y        = y;
       priv->sample.pressure = pressure;
       priv->sample.valid    = true;
+
+      add_ui_randomness((x << 16) ^ y ^ (pressure << 9));
     }
 
   /* Note the availability of new measurements */