>> I am playing around with it. I did the attached code. It is a usermode
>> program, which tries to map NULL, and a kernel module, which calls a NULL
>> pointer. The file badcode.bin contains an i386 ud2 instruction. When
>> loading the kernel module, while the usermode program is executing, I get
>> the usual NULL pointer dereference oops:
>
> You need to trigger the null pointer dereference from within the userspace
> program that maps NULL. The reason your test doesn't do anything is that it is
> the insmod tool whose address space gets used, as opposed to your nulltest
> program.
>
Think of a device driver which dereferences on read() or write() or ioctl.
Then the userspace program gets its chance, does not it?
Jan Engelhardt
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