From: Qian Cai <cai@xxxxxx>
Subject: mm/page_alloc: silence a KASAN false positive
kernel_init_free_pages() will use memset() on s390 to clear all pages from
kmalloc_order() which will override KASAN redzones because a redzone was
setup from the end of the allocation size to the end of the last page.
Silence it by not reporting it there. An example of the report is,
BUG: KASAN: slab-out-of-bounds in __free_pages_ok
Write of size 4096 at addr 000000014beaa000
Call Trace:
show_stack+0x152/0x210
dump_stack+0x1f8/0x248
print_address_description.isra.13+0x5e/0x4d0
kasan_report+0x130/0x178
check_memory_region+0x190/0x218
memset+0x34/0x60
__free_pages_ok+0x894/0x12f0
kfree+0x4f2/0x5e0
unpack_to_rootfs+0x60e/0x650
populate_rootfs+0x56/0x358
do_one_initcall+0x1f4/0xa20
kernel_init_freeable+0x758/0x7e8
kernel_init+0x1c/0x170
ret_from_fork+0x24/0x28
Memory state around the buggy address:
000000014bea9f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
000000014bea9f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>000000014beaa000: 03 fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
^
000000014beaa080: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
000000014beaa100: fe fe fe fe fe fe fe fe fe fe fe fe fe fe
Link: http://lkml.kernel.org/r/20200610052154.5180-1-cai@xxxxxx
Fixes: 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options")
Signed-off-by: Qian Cai <cai@xxxxxx>
Acked-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Tested-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 3 +++
1 file changed, 3 insertions(+)
--- a/mm/page_alloc.c~mm-page_alloc-silence-a-kasan-false-positive
+++ a/mm/page_alloc.c
@@ -1156,8 +1156,11 @@ static void kernel_init_free_pages(struc
{
int i;
+ /* s390's use of memset() could override KASAN redzones. */
+ kasan_disable_current();
for (i = 0; i < numpages; i++)
clear_highpage(page + i);
+ kasan_enable_current();
}
static __always_inline bool free_pages_prepare(struct page *page,
_
