From 6c50033dfb7a4dc7094d96f9339459b08b4efac9 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex.auvolat@ens.fr>
Date: Sun, 8 Mar 2015 11:10:45 +0100
Subject: Add PRNG

---
 src/kernel/Makefile       |  4 ++--
 src/kernel/core/kmain.c   | 10 ++++++++++
 src/kernel/core/prng.c    | 38 ++++++++++++++++++++++++++++++++++++++
 src/kernel/include/prng.h |  9 +++++++++
 4 files changed, 59 insertions(+), 2 deletions(-)
 create mode 100644 src/kernel/core/prng.c
 create mode 100644 src/kernel/include/prng.h

(limited to 'src/kernel')

diff --git a/src/kernel/Makefile b/src/kernel/Makefile
index 88a83e2..1a7c12e 100644
--- a/src/kernel/Makefile
+++ b/src/kernel/Makefile
@@ -2,14 +2,14 @@
 OBJ = core/loader.o core/dbglog.o \
 	core/gdt.o core/idt.o core/interrupt.o core/context_switch.o core/thread.o \
 	core/frame.o core/paging.o core/freemem.o core/region.o core/kmalloc.o \
-	core/worker.o \
+	core/worker.o core/prng.o \
 	user/vfs.o user/nullfs.o user/process.o user/elf.o user/syscall.o \
 	dev/pci.o dev/pciide.o \
 	fs/iso9660.o
 
 LIB = ../common/libc/libc.lib ../common/libkogata/libkogata.lib ../common/libalgo/libalgo.lib
 
-CFLAGS = -I ./include -I ../common/include
+CFLAGS = -I ./include -I ../common/include -DPRNG_INIT_ENTROPY=$(shell date +%N)
 
 LDFLAGS = -T linker.ld -Xlinker -Map=kernel.map
 
diff --git a/src/kernel/core/kmain.c b/src/kernel/core/kmain.c
index 5cd71c5..7cdd109 100644
--- a/src/kernel/core/kmain.c
+++ b/src/kernel/core/kmain.c
@@ -23,10 +23,16 @@
 #include <slab_alloc.h>
 #include <string.h>
 
+#include <prng.h>
+
 #include <dev/pci.h>
 #include <dev/pciide.h>
 #include <fs/iso9660.h>
 
+#ifndef PRNG_INIT_ENTROPY
+#define PRNG_INIT_ENTROPY 1299733235
+#endif
+
 // ===== FOR TESTS =====
 #define TEST_PLACEHOLDER_AFTER_IDT
 #define TEST_PLACEHOLDER_AFTER_REGION
@@ -149,6 +155,10 @@ void kernel_init_stage2(void* data) {
 	// Register FS drivers
 	register_iso9660_driver();
 
+	// Add entropy to prng
+	uint32_t x = PRNG_INIT_ENTROPY;
+	prng_add_entropy((uint8_t*)&x, sizeof(x));
+
 	// Parse command line
 	btree_t *cmdline = parse_cmdline((const char*)mbd->cmdline);
 
diff --git a/src/kernel/core/prng.c b/src/kernel/core/prng.c
new file mode 100644
index 0000000..d4307b6
--- /dev/null
+++ b/src/kernel/core/prng.c
@@ -0,0 +1,38 @@
+#include <prng.h>
+
+#define EPOOLSIZE 2048
+
+static uint32_t x = 211;
+static int n = 0;
+static char entropy[EPOOLSIZE];
+static int entropy_count = 0;
+static const uint32_t a = 16807;
+static const uint32_t m = 0x7FFFFFFF;
+
+uint16_t prng_word() {
+	if (++n == 100) {
+		n = 0;
+		if (entropy_count) {
+			entropy_count--;
+			x += entropy[entropy_count];
+		}
+	}
+	x = (x * a) % m;
+	return x & 0xFFFF;
+}
+
+void prng_bytes(uint8_t* out, size_t nbytes) {
+	uint16_t *d = (uint16_t*)out;
+	for (size_t i = 0; i < nbytes / 2; i++) {
+		d[i] = prng_word();
+	}
+	if (nbytes & 1) out[nbytes-1] = prng_word() & 0xFF;
+}
+
+void prng_add_entropy(const uint8_t* ptr, size_t nbytes) {
+	while (nbytes-- && entropy_count < EPOOLSIZE - 1) {
+		entropy[entropy_count++] = *(ptr++);
+	}
+}
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/
diff --git a/src/kernel/include/prng.h b/src/kernel/include/prng.h
new file mode 100644
index 0000000..0a9e036
--- /dev/null
+++ b/src/kernel/include/prng.h
@@ -0,0 +1,9 @@
+#include <stdint.h>
+#include <stddef.h>
+
+void prng_add_entropy(const uint8_t* ptr, size_t nbytes);	// add entropy to generator
+
+uint16_t prng_word();
+void prng_bytes(uint8_t* out, size_t nbytes);				// generate some bytes
+
+/* vim: set ts=4 sw=4 tw=0 noet :*/
-- 
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