From 4121d4481b72501aa4d22680be4ea1096d69d133 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Wed, 14 Dec 2022 13:35:42 +0100 Subject: bpf: Synchronize dispatcher update with bpf_dispatcher_xdp_func Hao Sun reported crash in dispatcher image [1]. Currently we don't have any sync between bpf_dispatcher_update and bpf_dispatcher_xdp_func, so following race is possible: cpu 0: cpu 1: bpf_prog_run_xdp ... bpf_dispatcher_xdp_func in image at offset 0x0 bpf_dispatcher_update update image at offset 0x800 bpf_dispatcher_update update image at offset 0x0 in image at offset 0x0 -> crash Fixing this by synchronizing dispatcher image update (which is done in bpf_dispatcher_update function) with bpf_dispatcher_xdp_func that reads and execute the dispatcher image. Calling synchronize_rcu after updating and installing new image ensures that readers leave old image before it's changed in the next dispatcher update. The update itself is locked with dispatcher's mutex. The bpf_prog_run_xdp is called under local_bh_disable and synchronize_rcu will wait for it to leave [2]. [1] https://lore.kernel.org/bpf/Y5SFho7ZYXr9ifRn@krava/T/#m00c29ece654bc9f332a17df493bbca33e702896c [2] https://lore.kernel.org/bpf/0B62D35A-E695-4B7A-A0D4-774767544C1A@gmail.com/T/#mff43e2c003ae99f4a38f353c7969be4c7162e877 Reported-by: Hao Sun Signed-off-by: Jiri Olsa Acked-by: Yonghong Song Acked-by: Paul E. McKenney Link: https://lore.kernel.org/r/20221214123542.1389719-1-jolsa@kernel.org Signed-off-by: Martin KaFai Lau --- kernel/bpf/dispatcher.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c index c19719f48ce0..fa3e9225aedc 100644 --- a/kernel/bpf/dispatcher.c +++ b/kernel/bpf/dispatcher.c @@ -125,6 +125,11 @@ static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs) __BPF_DISPATCHER_UPDATE(d, new ?: (void *)&bpf_dispatcher_nop_func); + /* Make sure all the callers executing the previous/old half of the + * image leave it, so following update call can modify it safely. + */ + synchronize_rcu(); + if (new) d->image_off = noff; } -- cgit v1.2.3