hammer: Store secret in rollback block

Also, increase console task stack size, as adding entropy
requires 780 bytes of stack.

BRANCH=none
BUG=b:38486828
TEST=Flash hammer
     rollbackinfo => 1 version 0 block, 1 empty block, RW verifies
           correctly.
     rollbackupdate 0; rollbackinfo => No change
     rollbackupdate 1; reboot => RO refuses to jump to RW
     rollbackinfo => Secret is [00..00] on both block (so the data
                     was copied correctly)
     rollbackupdate 2, 3, 4; rollbackinfo => Writes alternate
           between the 2 blocks.
     rollbackupdate 2 => Refuses to downgrade version
TEST=From blank secret [00..00], 'rollbackaddent Hello' updates it
         to [ba..fa], which matches the output of:
         (dd if=/dev/zero bs=1 count=32; echo -n Hello) | sha256sum

Change-Id: If63346dfab0a28aa82a7b4c2e46ca89fde3eb990
Reviewed-on: https://chromium-review.googlesource.com/511986
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
2 files changed