netdev - [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs

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Message-Id: <20210428161802.771519-1-jolsa@kernel.org>
Date:   Wed, 28 Apr 2021 18:18:02 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs

The recursion check in __bpf_prog_enter and __bpf_prog_exit
leaves some (not inlined) functions unprotected:

In __bpf_prog_enter:
  - migrate_disable is called before prog->active is checked

In __bpf_prog_exit:
  - migrate_enable,rcu_read_unlock_strict are called after
    prog->active is decreased

When attaching trampoline to them we get panic like:

  traps: PANIC: double fault, error_code: 0x0
  double fault: 0000 [#1] SMP PTI
  RIP: 0010:__bpf_prog_enter+0x4/0x50
  ...
  Call Trace:
   <IRQ>
   bpf_trampoline_6442466513_0+0x18/0x1000
   migrate_disable+0x5/0x50
   __bpf_prog_enter+0x9/0x50
   bpf_trampoline_6442466513_0+0x18/0x1000
   migrate_disable+0x5/0x50
   __bpf_prog_enter+0x9/0x50
   bpf_trampoline_6442466513_0+0x18/0x1000
   migrate_disable+0x5/0x50
   __bpf_prog_enter+0x9/0x50
   bpf_trampoline_6442466513_0+0x18/0x1000
   migrate_disable+0x5/0x50
   ...

Fixing this by adding deny list of btf ids for tracing
and ext programs and checking btf id during program
verification. Adding above functions to this list.

Suggested-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 kernel/bpf/verifier.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2579f6fbb5c3..4ffd64eaffda 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13112,6 +13112,17 @@ int bpf_check_attach_target(struct bpf_verifier_log *log,
 	return 0;
 }
 
+BTF_SET_START(btf_id_deny)
+BTF_ID_UNUSED
+#ifdef CONFIG_SMP
+BTF_ID(func, migrate_disable)
+BTF_ID(func, migrate_enable)
+#endif
+#if !defined CONFIG_PREEMPT_RCU && !defined CONFIG_TINY_RCU
+BTF_ID(func, rcu_read_unlock_strict)
+#endif
+BTF_SET_END(btf_id_deny)
+
 static int check_attach_btf_id(struct bpf_verifier_env *env)
 {
 	struct bpf_prog *prog = env->prog;
@@ -13171,6 +13182,10 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		ret = bpf_lsm_verify_prog(&env->log, prog);
 		if (ret < 0)
 			return ret;
+	} else if ((prog->type == BPF_PROG_TYPE_TRACING ||
+		    prog->type == BPF_PROG_TYPE_EXT) &&
+		   btf_id_set_contains(&btf_id_deny, btf_id)) {
+		return -EINVAL;
 	}
 
 	key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id);
-- 
2.30.2