[U-Boot] Does U-boot support ASLR?

[Mike Frysinger]

On Thursday 09 February 2012 13:37:15 Jason Markley wrote:

please don't top post, and keep the mailing list in cc

> I agree any proposal would need to be accompanied by good reasoning.
> I'm honestly a little confused as to why a generally accepted security
> feature such as ASLR would NOT be useful for u-boot.  U-boot has the
> capability to interact with the outside world via the network as well as
> the console.  When using the U-boot API, it also remains resident in
> memory.  Wouldn't something like ASLR enhance the security posture of
> U-boot in those situations?

u-boot is running in supervisor mode / ring 0 / etc...  you have full access 
to the hardware with a simple `mw` command.  randomizing the address base of 
u-boot doesn't gain you anything.  so no, i see no advantage of u-boot itself 
utilizing ASLR regardless of what it interacts with.

ignoring this, there are two fundamental issues with ASLR:
 - this early on, u-boot has very little (if no) entropy, so any attempts to 
generate random numbers are going to be fairly predictable
 - scripts that u-boot runs at boot time often times need a chunk of memory to 
load and boot stuff out of.  if u-boot could randomly be in the middle of that, 
then your board now randomly fails to boot.  the only way around that would be 
to have u-boot do virtual addresses, and that's clearly a non-starter.
-mike
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