Commit 35e3815f authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

bpf: Add deny list of btf ids check for tracing 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
programs and checking btf id during program verification.
Adding above functions to this list.

Suggested-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210429114712.43783-1-jolsa@kernel.org
parent 08389d88

kernel/bpf/verifier.c

+14 −0
Original line number Diff line number Diff line
@@ -13196,6 +13196,17 @@ 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;
@@ -13255,6 +13266,9 @@ 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 &&

		   btf_id_set_contains(&btf_id_deny, btf_id)) {

		return -EINVAL;

	}



	key = bpf_trampoline_compute_key(tgt_prog, prog->aux->attach_btf, btf_id);