userprogram:
virtualAddr = 0xc0010203 // randomly define virtual address
for(i = 0; i< SIZE; i++)
printf("%x", *(char*)(virtualAddr+i));
printf("%x", *(char*)(virtualAddr+i));
This program will give your segmentation fault when you run it.
Remember, CPU only understand virtual address.
Solution, write a kernel module to access any memory
#include <linux/module.h>
#include <linux/init.h>
#include <asm/io.h>
// 1G = 0x40000000
// trusted OS kernel code physical address is (0x400000, 0x620de5)
// add 1G, then test if it could access from this untrusted OS
#define PHYSTARTADDR 0x40400000
#define PHYENDADDR 0x40620de5
// this is the virtual address of kernel code
#define VIRSTARTADDR 0xc0400000
#define VIRENDADDR 0xc0620de5
#define SIZE 100
#include <linux/init.h>
#include <asm/io.h>
// 1G = 0x40000000
// trusted OS kernel code physical address is (0x400000, 0x620de5)
// add 1G, then test if it could access from this untrusted OS
#define PHYSTARTADDR 0x40400000
#define PHYENDADDR 0x40620de5
// this is the virtual address of kernel code
#define VIRSTARTADDR 0xc0400000
#define VIRENDADDR 0xc0620de5
#define SIZE 100
MODULE_LICENSE("Dual BSD/GPL");
static int hello_init(void)
{
char mem[SIZE];
int i;
void *virtualAddr ;
// if we want to access the memory range beyond current DIMM
// we could use ioremap to create the pagetables, so cpu will understand
// this virtual address. // we could use ioremap to create the pagetables, so cpu will understand
// virtualAddr = ioremap(PHYSTARTADDR, SIZE);
// this case, we just want to read all the current memory range,
// which is DIMM has been initialized. virtualAddr = VIRSTARTADDR;
for(i = 0; i< SIZE; i++)
printk("%x", *(char*)(virtualAddr+i));
printk("\nhello, world\n");
return 0;
}
static void hello_exit(void)
{
printk("Goodbye, crule world\n");
}
module_init(hello_init);
module_exit(hello_exit);
