diff options
| author | Alexander Potapenko <glider@google.com> | 2024-05-28 12:48:06 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-06-05 19:19:25 -0700 |
| commit | 2ef3cec44c60ae171b287db7fc2aa341586d65ba (patch) | |
| tree | f55c92430f01a4c594020af42344ec8dee417f2a /mm | |
| parent | 0105eaabb27f31d9b8d340aca6fb6a3420cab30f (diff) | |
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/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.com/T/
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>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/kmsan/core.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c index cf2d70e9c9a5..95f859e38c53 100644 --- a/mm/kmsan/core.c +++ b/mm/kmsan/core.c @@ -196,8 +196,7 @@ void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b, 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)); @@ -225,8 +224,16 @@ void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b, 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) |