linux-kernel - Re: [PATCH v9 01/10] btf: Add a new kfunc flag which allows to mark a function to be sleepable

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Date:   Wed, 10 Aug 2022 07:58:09 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Roberto Sassu <roberto.sassu@...wei.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        "martin.lau@...ux.dev" <martin.lau@...ux.dev>,
        "song@...nel.org" <song@...nel.org>, "yhs@...com" <yhs@...com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
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Subject: Re: [PATCH v9 01/10] btf: Add a new kfunc flag which allows to mark a
 function to be sleepable

On Wed, Aug 10, 2022 at 7:26 AM Benjamin Tissoires
<benjamin.tissoires@...hat.com> wrote:
>
> On Wed, Aug 10, 2022 at 3:44 PM Roberto Sassu <roberto.sassu@...wei.com> wrote:
> >
> > > From: Jarkko Sakkinen [mailto:jarkko@...nel.org]
> > > Sent: Tuesday, August 9, 2022 6:55 PM
> > > On Tue, Aug 09, 2022 at 03:45:54PM +0200, Roberto Sassu wrote:
> > > > From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > >
> > > > From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > >
> > > > This allows to declare a kfunc as sleepable and prevents its use in
> > > > a non sleepable program.
> > >
> > > Nit: "Declare a kfunc as sleepable and prevent its use in a
> > > non-sleepable program."
> > >
> > > It's missing the part *how* the patch accomplishes its goals.
> >
> > I will add:
> >
> > If an eBPF program is going to call a kfunc declared as sleepable,
> > eBPF will look at the eBPF program flags. If BPF_F_SLEEPABLE is
> > not set, execution of that program is denied.
>
> All those changes are looking good to me.
>
> Thanks a lot for keeping pushing on this patch :)

Multiple series other than the HID one started resending your patch
once you dropped it, it's obviously needed :) Thanks for sending it in
the first place :)

>
> Cheers,
> Benjamin
>
> >
> > Roberto
> >
> > > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > > Co-developed-by: Yosry Ahmed <yosryahmed@...gle.com>
> > > > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> > > > Signed-off-by: Hao Luo <haoluo@...gle.com>
> > > > ---
> > > >  Documentation/bpf/kfuncs.rst | 6 ++++++
> > > >  include/linux/btf.h          | 1 +
> > > >  kernel/bpf/btf.c             | 9 +++++++++
> > > >  3 files changed, 16 insertions(+)
> > > >
> > > > diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
> > > > index c0b7dae6dbf5..c8b21de1c772 100644
> > > > --- a/Documentation/bpf/kfuncs.rst
> > > > +++ b/Documentation/bpf/kfuncs.rst
> > > > @@ -146,6 +146,12 @@ that operate (change some property, perform some
> > > operation) on an object that
> > > >  was obtained using an acquire kfunc. Such kfuncs need an unchanged pointer
> > > to
> > > >  ensure the integrity of the operation being performed on the expected object.
> > > >
> > > > +2.4.6 KF_SLEEPABLE flag
> > > > +-----------------------
> > > > +
> > > > +The KF_SLEEPABLE flag is used for kfuncs that may sleep. Such kfuncs can
> > > only
> > > > +be called by sleepable BPF programs (BPF_F_SLEEPABLE).
> > > > +
> > > >  2.5 Registering the kfuncs
> > > >  --------------------------
> > > >
> > > > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > > > index cdb376d53238..976cbdd2981f 100644
> > > > --- a/include/linux/btf.h
> > > > +++ b/include/linux/btf.h
> > > > @@ -49,6 +49,7 @@
> > > >   * for this case.
> > > >   */
> > > >  #define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer
> > > arguments */
> > > > +#define KF_SLEEPABLE   (1 << 5) /* kfunc may sleep */
> > > >
> > > >  struct btf;
> > > >  struct btf_member;
> > > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > > > index 7e64447659f3..d3e4c86b8fcd 100644
> > > > --- a/kernel/bpf/btf.c
> > > > +++ b/kernel/bpf/btf.c
> > > > @@ -6175,6 +6175,7 @@ static int btf_check_func_arg_match(struct
> > > bpf_verifier_env *env,
> > > >  {
> > > >     enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> > > >     bool rel = false, kptr_get = false, trusted_arg = false;
> > > > +   bool sleepable = false;
> > > >     struct bpf_verifier_log *log = &env->log;
> > > >     u32 i, nargs, ref_id, ref_obj_id = 0;
> > > >     bool is_kfunc = btf_is_kernel(btf);
> > > > @@ -6212,6 +6213,7 @@ static int btf_check_func_arg_match(struct
> > > bpf_verifier_env *env,
> > > >             rel = kfunc_flags & KF_RELEASE;
> > > >             kptr_get = kfunc_flags & KF_KPTR_GET;
> > > >             trusted_arg = kfunc_flags & KF_TRUSTED_ARGS;
> > > > +           sleepable = kfunc_flags & KF_SLEEPABLE;
> > > >     }
> > > >
> > > >     /* check that BTF function arguments match actual types that the
> > > > @@ -6419,6 +6421,13 @@ static int btf_check_func_arg_match(struct
> > > bpf_verifier_env *env,
> > > >                     func_name);
> > > >             return -EINVAL;
> > > >     }
> > > > +
> > > > +   if (sleepable && !env->prog->aux->sleepable) {
> > > > +           bpf_log(log, "kernel function %s is sleepable but the program is
> > > not\n",
> > > > +                   func_name);
> > > > +           return -EINVAL;
> > > > +   }
> > > > +
> > > >     /* returns argument register number > 0 in case of reference release
> > > kfunc */
> > > >     return rel ? ref_regno : 0;
> > > >  }
> > > > --
> > > > 2.25.1
> > > >
> > >
> > > BR, Jarkko
> >
>