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kmsan: do not wipe out origin when doing partial unpoisoning

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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: f80be4571b ("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>
This commit is contained in:
Alexander Potapenko
2024-05-28 12:48:06 +02:00
committed by Andrew Morton
parent 0105eaabb2
commit 2ef3cec44c
1 changed files with 11 additions and 4 deletions
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13
mm/kmsan/core.c
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@@ -196,8 +196,7 @@ void kmsan_internal_set_shadow_origin(void *addr, size_t size, int b,
u32 origin, bool checked) u32 origin, bool checked)
{ {
u64 address = (u64)addr; u64 address = (u64)addr;
void *shadow_start; u32 *shadow_start, *origin_start;
u32 *origin_start;
size_t pad = 0; size_t pad = 0;
KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(addr, size)); 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 = origin_start =
(u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN); (u32 *)kmsan_get_metadata((void *)address, KMSAN_META_ORIGIN);
for (int i = 0; i < size / KMSAN_ORIGIN_SIZE; i++) /*
* 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; origin_start[i] = origin;
}
} }
struct page *kmsan_vmalloc_to_page_or_null(void *vaddr) struct page *kmsan_vmalloc_to_page_or_null(void *vaddr)