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* [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs
@ 2021-04-28 16:18 Jiri Olsa
  2021-04-28 19:41 ` Andrii Nakryiko
  0 siblings, 1 reply; 3+ messages in thread
From: Jiri Olsa @ 2021-04-28 16:18 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko
  Cc: netdev, bpf, Martin KaFai Lau, Song Liu, Yonghong Song,
	John Fastabend, KP Singh

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@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.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


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs
  2021-04-28 16:18 [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs Jiri Olsa
@ 2021-04-28 19:41 ` Andrii Nakryiko
  2021-04-29 11:24   ` Jiri Olsa
  0 siblings, 1 reply; 3+ messages in thread
From: Andrii Nakryiko @ 2021-04-28 19:41 UTC (permalink / raw)
  To: Jiri Olsa
  Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Networking,
	bpf, Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend,
	KP Singh

On Wed, Apr 28, 2021 at 9:19 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> 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@kernel.org>
> Signed-off-by: Jiri Olsa <jolsa@kernel.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) &&

BPF_PROG_TYP_EXT can only replace other BPF programs/subprograms, it
can't replace kernel functions, so the deny list shouldn't be checked
for them.

> +                  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
>

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs
  2021-04-28 19:41 ` Andrii Nakryiko
@ 2021-04-29 11:24   ` Jiri Olsa
  0 siblings, 0 replies; 3+ messages in thread
From: Jiri Olsa @ 2021-04-29 11:24 UTC (permalink / raw)
  To: Andrii Nakryiko
  Cc: Jiri Olsa, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
	Networking, bpf, Martin KaFai Lau, Song Liu, Yonghong Song,
	John Fastabend, KP Singh

On Wed, Apr 28, 2021 at 12:41:34PM -0700, Andrii Nakryiko wrote:
> On Wed, Apr 28, 2021 at 9:19 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > 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@kernel.org>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.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) &&
> 
> BPF_PROG_TYP_EXT can only replace other BPF programs/subprograms, it
> can't replace kernel functions, so the deny list shouldn't be checked
> for them.

right, will send new version

jirka

> 
> > +                  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
> >
> 


^ permalink raw reply	[flat|nested] 3+ messages in thread

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Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-04-28 16:18 [PATCH] bpf: Add deny list of btf ids check for tracing and ext programs Jiri Olsa
2021-04-28 19:41 ` Andrii Nakryiko
2021-04-29 11:24   ` Jiri Olsa

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