From d7c4536c91ddd307fc9b99984ac49b5b5459b485 Mon Sep 17 00:00:00 2001
From: Camil Staps
Date: Mon, 30 Nov 2015 22:08:58 +0100
Subject: Assignment 2, 3

---
 CamilStaps-s4498062-Assignment-2/ex2/Makefile    |  8 ++++++++
 CamilStaps-s4498062-Assignment-2/ex2/ex2.txt     | 20 ++++++++++++++++++++
 CamilStaps-s4498062-Assignment-2/ex2/hello-cr4.c | 22 ++++++++++++++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 CamilStaps-s4498062-Assignment-2/ex2/Makefile
 create mode 100644 CamilStaps-s4498062-Assignment-2/ex2/ex2.txt
 create mode 100644 CamilStaps-s4498062-Assignment-2/ex2/hello-cr4.c

(limited to 'CamilStaps-s4498062-Assignment-2/ex2')

diff --git a/CamilStaps-s4498062-Assignment-2/ex2/Makefile b/CamilStaps-s4498062-Assignment-2/ex2/Makefile
new file mode 100644
index 0000000..a87a542
--- /dev/null
+++ b/CamilStaps-s4498062-Assignment-2/ex2/Makefile
@@ -0,0 +1,8 @@
+obj-m += hello-cr4.o
+
+all:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
+
diff --git a/CamilStaps-s4498062-Assignment-2/ex2/ex2.txt b/CamilStaps-s4498062-Assignment-2/ex2/ex2.txt
new file mode 100644
index 0000000..35afd58
--- /dev/null
+++ b/CamilStaps-s4498062-Assignment-2/ex2/ex2.txt
@@ -0,0 +1,20 @@
+a
+    According to https://en.wikipedia.org/wiki/Control_register#CR4, the SMAP and SMEP bits are used to protect ring 0.
+    If writing to CR4 would be allowed, we could disable this protection, and access kernel space data (e.g.)
+
+b
+    0x40050e <main+8>           mov     %cr4,%rax
+
+    This attempts to move the RAX register to the CR4 register, i.e. to write to CR4.
+
+c
+    Done. I suppose it isn't necessary to give you the code or results, as all was needed was copying from the given website.
+
+d
+    See hello-cr4.c and Makefile.
+    
+    # make
+    [..]
+    # insmod hello-cr4.ko
+    [15892.352286] Hello world! CR4 =         7f0
+
diff --git a/CamilStaps-s4498062-Assignment-2/ex2/hello-cr4.c b/CamilStaps-s4498062-Assignment-2/ex2/hello-cr4.c
new file mode 100644
index 0000000..9db671d
--- /dev/null
+++ b/CamilStaps-s4498062-Assignment-2/ex2/hello-cr4.c
@@ -0,0 +1,22 @@
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Camil Staps");
+MODULE_DESCRIPTION("A Simple Hello World module");
+
+static int __init hello_init(void) {
+    unsigned long long result;
+    __asm__("movq %%cr4, %%rax\n" : "=a"(result));
+    printk(KERN_INFO "Hello world! CR4 = %11x\n", result);
+    return 0;
+}
+
+static void __exit hello_cleanup(void) {
+    printk(KERN_INFO "Cleaning up module.\n");
+}
+
+module_init(hello_init);
+module_exit(hello_cleanup);
+
-- 
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