I have a question about changing the page attributes of the
system call table.
I am writing a kernel module that does some system call interposition.
This works fine on my debian system, but apparently the stock Fedora
kernel (2.6.22) has the system call table write protected. So I would like
the module to add write permissions to the system call table before
it modifies it.
This is the code in my init_module that is problematic:
// Storing the original call
orig_kill = sys_call_table[__NR_kill];
// Change to write
pg = virt_to_page(sys_call_table);
change_page_attr(pg, 1, PAGE_KERNEL);
global_flush_tlb();
// Test write, should change nothing, but oopses instead
sys_call_table[__NR_kill] = (void*)orig_kill;
I imagine that I'm doing something obviously wrong; I've only been looking
at kernel code for a couple weeks. Can someone please explain what my
error is?
-Hajime Inoue
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