kmsan: do not wipe out origin when doing partial unpoisoning

As noticed by Brian, KMSAN should not be zeroing the origin when
unpoisoning parts of a four-byte uninitialized value, e.g.:

    char a[4];
    kmsan_unpoison_memory(a, 1);

This led to false negatives, as certain poisoned values could receive zero
origins, preventing those values from being reported.

To fix the problem, check that kmsan_internal_set_shadow_origin() writes
zero origins only to slots which have zero shadow.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: f80be4571b19 ("kmsan: add KMSAN runtime core")
Signed-off-by: Alexander Potapenko <[email protected]>
Reported-by: Brian Johannesmeyer <[email protected]>
  Link: https://lore.kernel.org/lkml/[email protected]/T/
Reviewed-by: Marco Elver <[email protected]>
Tested-by: Brian Johannesmeyer <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions