linux-kernel - [PATCH AUTOSEL 6.3 32/59] bpf: Add preempt_count

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Date:   Thu,  4 May 2023 15:41:15 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Yafang <laoar.shao@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jiri Olsa <olsajiri@...il.com>, Hao Luo <haoluo@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <sashal@...nel.org>, daniel@...earbox.net,
        andrii@...nel.org, bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 6.3 32/59] bpf: Add preempt_count_{sub,add} into btf id deny list

From: Yafang <laoar.shao@...il.com>

[ Upstream commit c11bd046485d7bf1ca200db0e7d0bdc4bafdd395 ]

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]  <TASK>
[  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 <rostedt@...dmis.org>
Signed-off-by: Yafang <laoar.shao@...il.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Jiri Olsa <olsajiri@...il.com>
Acked-by: Hao Luo <haoluo@...gle.com>
Link: https://lore.kernel.org/r/20230413025248.79764-1-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 767e8930b0bd5..d8a01180ddf76 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17551,6 +17551,10 @@ 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)
-- 
2.39.2