Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall | Date | Thu, 2 May 2019 16:34:46 +0000 |
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From: Ingo Molnar > Sent: 02 May 2019 16:09 > * Andy Lutomirski <luto@kernel.org> wrote: > > > Or we decide that calling get_random_bytes() is okay with IRQs off and > > this all gets a bit simpler. > > BTW., before we go down this path any further, is the plan to bind this > feature to a real CPU-RNG capability, i.e. to the RDRAND instruction, > which excludes a significant group of x86 of CPUs?
It has already been measured - it is far too slow. Even just using 6 bits so it doesn't have to be read every system call is probably a significant overhead (I don't think that was tested though).
I do agree that using 'real' randomness is probably OTT here.
> Because calling tens of millions of system calls per second will deplete > any non-CPU-RNG sources of entropy and will also starve all other users > of random numbers, which might have a more legitimate need for > randomness, such as the networking stack ...
If the function you use to generate random numbers from the 'entropy pool' isn't reversible (in a finite time) I don't think you really need to worry about bits-in v bits-out.
David
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