Commit c89e843a authored by Hou Tao's avatar Hou Tao Committed by Martin KaFai Lau
Browse files

bpf: Use this_cpu_{inc_return|dec} for prog->active 



Both __this_cpu_inc_return() and __this_cpu_dec() are not preemption
safe and now migrate_disable() doesn't disable preemption, so the update
of prog-active is not atomic and in theory under fully preemptible kernel
recurisve prevention may do not work.

Fixing by using the preemption-safe and IRQ-safe variants.

Fixes: ca06f55b ("bpf: Add per-program recursion prevention mechanism")
Signed-off-by: default avatarHou Tao <houtao1@huawei.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20220901061938.3789460-3-houtao@huaweicloud.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent 197827a0

kernel/bpf/trampoline.c

+4 −4
Original line number Diff line number Diff line
@@ -895,7 +895,7 @@ u64 notrace __bpf_prog_enter(struct bpf_prog *prog, struct bpf_tramp_run_ctx *ru 


	run_ctx->saved_run_ctx = bpf_set_run_ctx(&run_ctx->run_ctx);



	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {

	if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) {

		inc_misses_counter(prog);

		return 0;

	}
@@ -930,7 +930,7 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_ 
	bpf_reset_run_ctx(run_ctx->saved_run_ctx);



	update_prog_stats(prog, start);

	__this_cpu_dec(*(prog->active));

	this_cpu_dec(*(prog->active));

	migrate_enable();

	rcu_read_unlock();

}
@@ -966,7 +966,7 @@ u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_r 
	migrate_disable();

	might_fault();



	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {

	if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) {

		inc_misses_counter(prog);

		return 0;

	}
@@ -982,7 +982,7 @@ void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start, 
	bpf_reset_run_ctx(run_ctx->saved_run_ctx);



	update_prog_stats(prog, start);

	__this_cpu_dec(*(prog->active));

	this_cpu_dec(*(prog->active));

	migrate_enable();

	rcu_read_unlock_trace();

}