Messages in this thread | | | Date | Mon, 3 Feb 2014 11:37:29 -0500 | From | Theodore Ts'o <> | Subject | Re: [PATCH,RFC] random: collect cpu randomness |
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On Mon, Feb 03, 2014 at 10:50:42AM -0500, Jörn Engel wrote: > If the measurement event is an interrupt and the CPU has a > cycle-counter, you are set. On interesting systems lacking a > cycle-counter, we still have a high-resolution counter or sorts that > is the CPU itself. > > Instruction pointer and stack pointer for both kernel and userland are > one way to read out the "counter". Main problem here are tight loops > where your "counter" is not high-resolution at all. But something > within the CPU is constantly changing. And that something tends to be > contained in the registers. > > How about taking the saved registers from the interrupted CPU, xor'ing > them all and calling the result random_get_entropy() on systems > lacking a good cycles-counter?
So we could take the struct pt_regs which we get from get_irq_regs(), XOR them together and use them to feed into input[2] amd input[3] in add_interrupt_randomness(). Or some other way of distributing the values of all of the irq registers into the __u32 input[4] array.
That would probably be a good and useful thing to do. Was that basically what you were suggesting?
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