From: Alexei Starovoitov <ast@kernel.org>
Date: Mon, 20 Jan 2020 19:22:31 -0800
Subject: bpf: Fix trampoline usage in preempt
Patch-mainline: v5.6-rc1
Git-commit: 05d57f1793fb250c85028c9952c3720010baa853
References: bsc#1154353 bsc#1177028
Though the second half of trampoline page is unused a task could be
preempted in the middle of the first half of trampoline and two
updates to trampoline would change the code from underneath the
preempted task. Hence wait for tasks to voluntarily schedule or go
to userspace. Add similar wait before freeing the trampoline.
Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline")
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/bpf/20200121032231.3292185-1-ast@kernel.org
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Acked-by: Gary Lin <glin@suse.com>
---
kernel/bpf/trampoline.c | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -160,6 +160,14 @@ static int bpf_trampoline_update(struct
if (fexit_cnt)
flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
+ /* Though the second half of trampoline page is unused a task could be
+ * preempted in the middle of the first half of trampoline and two
+ * updates to trampoline would change the code from underneath the
+ * preempted task. Hence wait for tasks to voluntarily schedule or go
+ * to userspace.
+ */
+ synchronize_rcu_tasks();
+
err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2,
&tr->func.model, flags,
fentry, fentry_cnt,
@@ -251,6 +259,8 @@ void bpf_trampoline_put(struct bpf_tramp
goto out;
if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
goto out;
+ /* wait for tasks to get out of trampoline before freeing it */
+ synchronize_rcu_tasks();
bpf_jit_free_exec(tr->image);
hlist_del(&tr->hlist);
kfree(tr);