[Cerowrt-devel] getting more randomness by improving MIPS get_cycles()
stephen at networkplumber.org
Mon Sep 9 11:16:45 EDT 2013
On Sun, 8 Sep 2013 12:04:27 -0700
Dave Taht <dave.taht at bufferbloat.net> wrote:
> In light of the whole nsa hoo-ra (stuff like this)
> Ted Tso has pointed out to me that apparently mips' does not have a working
> generic get_cycles() call, but instead returns 0 in all cases.
> e.g: In arch/mips/include/asm/timex.h:
> typedef unsigned int cycles_t;
> static inline cycles_t get_cycles(void)
> return 0;
> get_cycles() is used in innumerable places in random.c.
> This is double plus ungood... I am REALLY hoping I'm merely misreading
> the code...
> An example:
> (see drivers/char/random.c for how often it is used)
> * Add device- or boot-specific data to the input and nonblocking
> * pools to help initialize them to unique values.
> * None of this adds any entropy, it is meant to avoid the
> * problem of the nonblocking pool having similar initial state
> * across largely identical devices.
> void add_device_randomness(const void *buf, unsigned int size)
> unsigned long time = get_cycles() ^ jiffies;
> So, what blocks having a working get_cycles in common mips architectures?
In order to implement get_cycles() a high resolution hardware counter
with quick access is necessary.
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