crossystem: Add a fake workbuffer for the fake context

crossystem functions just make up a fake vb2_context for calling into
things like vb2_nv_init(), but that function actually accesses
vb2_shared_data as well. This used to work because vb2_get_sd() would
return NULL in that case and vb2_nv_init() actually checks for that,
but with the persistent context model this is no longer possible and
making up directly allocated contexts is always illegal.

This patch adds a small fake workbuffer to the fake context so we can
have real backing storage for shared data. (This might not be the final
way we want to fix it but should work as a quick band-aid over the
crashes.)

Also remove the now pointless (sd == NULL) checks from vb2_nv_init().

BRANCH=None
BUG=chromium:1024732
TEST=make runtests

Change-Id: I91247013f092bbfc41cf1974b82cf70a29fa4734
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1917486
Tested-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Queue: Brian Norris <briannorris@chromium.org>
3 files changed