From: Alexei Starovoitov ast@kernel.org
commit 05d57f1793fb250c85028c9952c3720010baa853 upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/bpf/trampoline.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -150,6 +150,14 @@ 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, &tr->func.model, flags, fentry, fentry_cnt, fexit, fexit_cnt, @@ -240,6 +248,8 @@ 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);