linux-kernel - Re: IRQF_SAMPLE

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Message-ID: <200904071830.38081.rgetz@blackfin.uclinux.org>
Date:	Tue, 7 Apr 2009 18:30:37 -0400
From:	Robin Getz <rgetz@...ckfin.uclinux.org>
To:	"Chris Peterson" <cpeterso@...terso.com>
CC:	"Matt Mackall" <mpm@...enic.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: IRQF_SAMPLE_RANDOM question...

On Tue 7 Apr 2009 17:39, Chris Peterson pondered:
> 1. Are there any new add_*_randomness() functions that could be added?

I can think of - USB, serial, SDIO - but if any are heavily loaded with 
constant data - their randomness reduces, and becomes less useful. if it is 
the normal use case - then these might be better - but it is a function of 
the local users's use of the device - and is not remotely attackable.

> Some userspace daemons like EGD (running as root) feed random system
> info (e.g. vmstat) into /dev/random. But how many Linux distros
> actually run entropy-gathering daemons by default?

Not many that I can find.

> Would /dev/random 
> be more secure if entropy-gathering daemons were replaced with new
> kernel functions like add_vmstat_randomness() or add_ps_randomness()?

on embedded and server - it is likely most of ps (except load) will be pretty 
stable - even vmstat - might be on more stable than you think on embedded - 
which starts processes, allocates memory, and then just runs forever.....

> 2. Are there any other functions that could be calling the existing
> add_*_randomness() functions? Currently:
> 
> * add_input_randomness() is called from input_event().

Could be added in the serial core? usb? spi? i2c?

> * add_interrupt_randomess() is called from handle_IRQ_event() if
>    IRQF_SAMPLE_RANDOM is set.
> * add_disk_randomness() is called from blk_end_io() and __blk_end_request().
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