[PATCH 5.19 222/717] bpf: Use this_cpu_{inc_return|dec} for prog->active

Greg Kroah-Hartman
2022-10-22T07:56:16Z

From: Hou Tao <houtao1@huawei.com>

[ Upstream commit c89e843a11f1075d27684f6b42256213e4592383 ]

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: ca06f55b9002 ("bpf: Add per-program recursion prevention mechanism")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20220901061938.3789460-3-houtao@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/trampoline.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 93c7675f0c9e..fe4f4d9d043b 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -585,7 +585,7 @@ 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;
}
@@ -620,7 +620,7 @@ 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();
}
@@ -631,7 +631,7 @@ 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;
}
@@ -647,7 +647,7 @@ 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();
}
--
2.35.1