Linux Kernel Module Cheat

Only tested in x86_64.

The Linux kernel exposes physical addresses to userland through:

In this section we will play with them.

The following files contain examples to access that data and test it out:

First get a virtual address to play with:

./posix/virt_to_phys_test.out &

Sample output:

vaddr 0x600800
pid 110

The program:

allocates a volatile variable and sets is value to 0x12345678
prints the virtual address of the variable, and the program PID
runs a while loop until until the value of the variable gets mysteriously changed somehow, e.g. by nasty tinkerers like us

Then, translate the virtual address to physical using /proc/<pid>/maps and /proc/<pid>/pagemap:

./linux/virt_to_phys_user.out 110 0x600800

Sample output physical address:

0x7c7b800

Now we can verify that linux/virt_to_phys_user.out gave the correct physical address in the following ways:

Bibliography: