6.6-stable review patch. If anyone has any objections, please let me know.
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From: Alexander Potapenko glider@google.com
commit 2ef3cec44c60ae171b287db7fc2aa341586d65ba upstream.
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/20240528104807.738758-1-glider@google.com Fixes: f80be4571b19 ("kmsan: add KMSAN runtime core") Signed-off-by: Alexander Potapenko glider@google.com Reported-by: Brian Johannesmeyer bjohannesmeyer@gmail.com Link: https://lore.kernel.org/lkml/20240524232804.1984355-1-bjohannesmeyer@gmail.c... Reviewed-by: Marco Elver elver@google.com Tested-by: Brian Johannesmeyer bjohannesmeyer@gmail.com Cc: Dmitry Vyukov dvyukov@google.com Cc: Kees Cook keescook@chromium.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/kmsan/core.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)
--- a/mm/kmsan/core.c +++ b/mm/kmsan/core.c @@ -262,8 +262,7 @@ void kmsan_internal_set_shadow_origin(vo u32 origin, bool checked) { u64 address = (u64)addr; - void *shadow_start; - u32 *origin_start; + u32 *shadow_start, *origin_start; size_t pad = 0;
KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size)); @@ -291,8 +290,16 @@ void kmsan_internal_set_shadow_origin(vo origin_start = (u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
- for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++) - origin_start[i] = origin; + /* + * If the new origin is non-zero, assume that the shadow byte is also non-zero, + * and unconditionally overwrite the old origin slot. + * If the new origin is zero, overwrite the old origin slot iff the + * corresponding shadow slot is zero. + */ + for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++) { + if (origin || !shadow_start[i]) + origin_start[i] = origin; + } }
struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)