[coreboot] Rowhammer mitigation: RH activation probability

[Taiidan at gmx.com]

On 12/07/2018 03:28 PM, emanuele wrote:
> Hello everyone,
> I know some system has support for a particular feature against
> Rowhammer attack.
> The "RH activation probability" settings allows to refresh a row with a
> tunable probability.
> 
> For example some AMI BIOS version include this option:
> https://forums.puri.sm/t/row-hammer/793/7

I would like to note that company has provided poor security advice on a
variety of occasions - if you want good advice I would ask people here
or on the gentoo ML since both seem to have a large amount of
experts...I also provide free advice for expert level technical
questions so you can email me as well.

> 
> I have found a trace in coreboot code here:
> https://github.com/siro20/coreboot/blob/master/src/vendorcode/intel/fsp/fsp2_0/cannonlake/FspmUpd.h

Do you mean this and its related options?

/** Offset 0x04AB - Enable RH Prevention
  Enables/Disable RH Prevention
  $EN_DIS
**/

/** Offset 0x04F7 - Row Hammer Solution
  Type of method used to prevent Row Hammer. Default is Hardware RHP
  0:Hardware RHP, 1:2x Refresh
**/

It appears the same as in the screenshot since AMI BIOS like coreboot
uses Intel FSP for hardware init (all new intel hardware uses fsp blobs
for hw init)

AFAIK there aren't any non development boards that use cannonlake and
since the hardware initiation is blobbed it would be hard to find out
how it works or test it to see if really does what it says unless we can
get someone from intel to comment here.

In my experience proprietary firmware frequently has options that aren't
actually implemented or don't do what they say they do.

> 
> Anyone know if this option is currently available on coreboot?


rowhammer is almost entirely a laptop problem or for that matter
anything that uses SODIMM's due to their high density.

The ivy/sandybridge hw init code like for x220/t420/w520 laptops etc had
its ram refresh rates doubled a few years back to fix the rowhammer
problem similarly to the second option in the bios screenshot you linked.

No idea about any other coreboot laptops and I am interested to know
about the AGESA series like the g505s (which have open cpu/ram hw init)

The expensive laptops with ECC are not really worth it since ECC doesn't
fix the issue...although one might be alerted from errors in the log and
could set the system to halt if any pop up preventing whatever the evil
program wants to do.

> Thank you all!

Yea hello and welcome :D