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

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Date:   Fri, 15 Nov 2019 16:05:59 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        netdev@...r.kernel.org,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Matteo Croce <mcroce@...hat.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: [net-next v1 PATCH 1/4] xdp: remove memory poison on free for
 struct xdp_mem_allocator

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@...hat.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);
 }