From: Alexei Starovoitov

Debugging of BPF programs needs some form of printk from the program,
so let programs call limited trace_printk() with %d %u %x %p modifiers only.

Should anyone be allowed to use BPF programs to determine the kernel
addresses of any items?
Looks as though it is leaking kernel addresses to userspace.
Note that the problem is with the arguments, not the format string.

	David