Hi Chan,
Thank you for pointing me to the right direction.
Pointer Types
=============
Pointers printed without a specifier extension (i.e unadorned %p) are hashed to give a unique identifier without leaking kernel addresses to user space. On 64 bit machines the first 32 bits are zeroed. If you _really_ want the address see %px below.
On Jan 14, 2022, at 01:36, Chan Kim < ckim@xxxxxxxxxx> wrote:
Hi,
To print kernel virtual address, you should use %px instead of %p in the printk.
Probably that’s why you couldn’t see the pointer values correctly.
Chan
From: admin LI <admin@xxxxxxxxxxxxx>
Sent: Friday, January 14, 2022 6:02 AM
To: kernelnewbies@xxxxxxxxxxxxxxxxx
Subject: How to disable address randomization ?
Hi,
I'm developing a kernel module for an ARM machine, while debugging I found addresses
printed are all randomized and useless for debugging.
To prove I was not crazy I wrote this small program:
---------------------------------
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Somebody");
MODULE_DESCRIPTION("A simple example Linux module.");
MODULE_VERSION("0.01");
static int __init example_init(void) {
uint32_t a;
uint32_t b;
uint32_t c;
uint8_t d[10];
uint8_t *e;
printk(KERN_INFO "Hello, World!\n");
printk(KERN_INFO "&a %p\n",&a);
printk(KERN_INFO "&b %p\n",&b);
printk(KERN_INFO "&c %p\n",&c);
printk(KERN_INFO "&d %p\n",d);
printk(KERN_INFO "&d[0] %p\n",&d[0]);
printk(KERN_INFO "&d[1] %p\n",&d[1]);
e = kmalloc(10, GFP_KERNEL);
printk(KERN_INFO "&e[0] %p\n",&e[0]);
printk(KERN_INFO "&e[1] %p\n",&e[1]);
kfree(e);
return 0;
}
static void __exit example_exit(void) {
printk(KERN_INFO "Goodbye, World!\n");
}
module_init(example_init);
module_exit(example_exit);
---------------------------------
And it gave me this output:
Hello, World!
&a b3f9fa31
&b 27e1c68a
&c da50d287
&d 9f9aec2b
&d[0] 9f9aec2b
&d[1] cc627580
&e[0] 98b8c9eb
&e[1] 45f248f8
Then I tested on my debian host machine which gave me the same kind of randomized addresses.
When I search randomization the only thing I found is KASLR which I don't think is the same thing.
|
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