From c11bd046485d7bf1ca200db0e7d0bdc4bafdd395 Mon Sep 17 00:00:00 2001 From: Yafang Date: Thu, 13 Apr 2023 02:52:48 +0000 Subject: [PATCH] bpf: Add preempt_count_{sub,add} into btf id deny list The recursion check in __bpf_prog_enter* and __bpf_prog_exit* leave preempt_count_{sub,add} unprotected. When attaching trampoline to them we get panic as follows, [ 867.843050] BUG: TASK stack guard page was hit at 0000000009d325cf (stack is 0000000046a46a15..00000000537e7b28) [ 867.843064] stack guard page: 0000 [#1] PREEMPT SMP NOPTI [ 867.843067] CPU: 8 PID: 11009 Comm: trace Kdump: loaded Not tainted 6.2.0+ #4 [ 867.843100] Call Trace: [ 867.843101] [ 867.843104] asm_exc_int3+0x3a/0x40 [ 867.843108] RIP: 0010:preempt_count_sub+0x1/0xa0 [ 867.843135] __bpf_prog_enter_recur+0x17/0x90 [ 867.843148] bpf_trampoline_6442468108_0+0x2e/0x1000 [ 867.843154] ? preempt_count_sub+0x1/0xa0 [ 867.843157] preempt_count_sub+0x5/0xa0 [ 867.843159] ? migrate_enable+0xac/0xf0 [ 867.843164] __bpf_prog_exit_recur+0x2d/0x40 [ 867.843168] bpf_trampoline_6442468108_0+0x55/0x1000 ... [ 867.843788] preempt_count_sub+0x5/0xa0 [ 867.843793] ? migrate_enable+0xac/0xf0 [ 867.843829] __bpf_prog_exit_recur+0x2d/0x40 [ 867.843837] BUG: IRQ stack guard page was hit at 0000000099bd8228 (stack is 00000000b23e2bc4..000000006d95af35) [ 867.843841] BUG: IRQ stack guard page was hit at 000000005ae07924 (stack is 00000000ffd69623..0000000014eb594c) [ 867.843843] BUG: IRQ stack guard page was hit at 00000000028320f0 (stack is 00000000034b6438..0000000078d1bcec) [ 867.843842] bpf_trampoline_6442468108_0+0x55/0x1000 ... That is because in __bpf_prog_exit_recur, the preempt_count_{sub,add} are called after prog->active is decreased. Fixing this by adding these two functions into btf ids deny list. Suggested-by: Steven Rostedt Signed-off-by: Yafang Cc: Masami Hiramatsu Cc: Steven Rostedt Cc: Jiri Olsa Acked-by: Hao Luo Link: https://lore.kernel.org/r/20230413025248.79764-1-laoar.shao@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d6db6de3e9eaa8..e3d5a7a2f4280c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -18582,6 +18582,10 @@ BTF_ID(func, migrate_enable) #if !defined CONFIG_PREEMPT_RCU && !defined CONFIG_TINY_RCU BTF_ID(func, rcu_read_unlock_strict) #endif +#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_TRACE_PREEMPT_TOGGLE) +BTF_ID(func, preempt_count_add) +BTF_ID(func, preempt_count_sub) +#endif BTF_SET_END(btf_id_deny) static bool can_be_sleepable(struct bpf_prog *prog)