[net-next v1 PATCH 1/4] xdp: remove memory poison on free for struct xdp_mem_allocator

Jesper Dangaard Brouer
2019-11-15T15:06:13Z

When looking at the details I realised that the memory poison in
__xdp_mem_allocator_rcu_free doesn't make sense. This is because the
SLUB allocator uses the first 16 bytes (on 64 bit), for its freelist,
which overlap with members in struct xdp_mem_allocator, that were
updated. Thus, SLUB already does the "poisoning" for us.

I still believe that poisoning memory make sense in other cases.
Kernel have gained different use-after-free detection mechanism, but
enabling those is associated with a huge overhead. Experience is that
debugging facilities can change the timing so much, that that a race
condition will not be provoked when enabled. Thus, I'm still in favour
of poisoning memory where it makes sense.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
net/core/xdp.c | 5 -----
1 file changed, 5 deletions(-)

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 8e405abaf05a..e334fad0a6b8 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -73,11 +73,6 @@ static void __xdp_mem_allocator_rcu_free(struct rcu_head *rcu)
/* Allow this ID to be reused */
ida_simple_remove(&mem_id_pool, xa->mem.id);

- /* Poison memory */
- xa->mem.id = 0xFFFF;
- xa->mem.type = 0xF0F0;
- xa->allocator = (void *)0xDEAD9001;
-
kfree(xa);
}