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

[Jason Markley (ggsg) <jamarkle@ggsg.cisco.com>]

On 2/9/12 2:50 PM, Mike Frysinger wrote:
> On Thursday 09 February 2012 14:28:07 Scott Wood wrote:
>> On 02/09/2012 12:58 PM, Mike Frysinger wrote:
>>> On Thursday 09 February 2012 13:37:15 Jason Markley wrote:
>>>> 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.
>> This assumes that the full command line interface is enabled, and is the
>> mechanism of interaction in question.  It doesn't apply to interactions
>> over the network, special serial protocols, etc.
> network/serial loads do no file length checks.  `tftpload 0` will write until 
> the server stops sending.  not to mention there is no secure communication 
> between u-boot and the server.
And having TFTP as an option in such a 'secure' boot loader would
probably not make it past the checks necessary.  So if it helps, assume
that when someone is wanting to use ASLR, they also would configure
U-boot to not have the tftpload command available.

-Jason
>
>>> 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
>> This doesn't apply if there's a hardware random number generator -- and
>> even poor entropy is more effort to guess than a fixed address.
> not when you know the starting point and can brute force it through
>
>> It probably doesn't make sense as default behavior, but I could see it
>> being useful in some situations.
> such as ?
> -mike
>
>
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