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    SubjectRe: [PATCH bpf-next v6 3/8] bpf: lsm: provide attachment points for BPF LSM programs
    On 25-Mär 12:28, Kees Cook wrote:
    > On Wed, Mar 25, 2020 at 04:26:24PM +0100, KP Singh wrote:
    > > From: KP Singh <kpsingh@google.com>
    > >
    > > When CONFIG_BPF_LSM is enabled, nop functions, bpf_lsm_<hook_name>, are
    > > generated for each LSM hook. These functions are initialized as LSM
    > > hooks in a subsequent patch.
    > >
    > > Signed-off-by: KP Singh <kpsingh@google.com>
    > > Reviewed-by: Brendan Jackman <jackmanb@google.com>
    > > Reviewed-by: Florent Revest <revest@google.com>
    > > Reviewed-by: Kees Cook <keescook@chromium.org>
    > > Acked-by: Yonghong Song <yhs@fb.com>
    > > ---
    > > include/linux/bpf_lsm.h | 22 ++++++++++++++++++++++
    > > kernel/bpf/bpf_lsm.c | 14 ++++++++++++++
    > > 2 files changed, 36 insertions(+)
    > > create mode 100644 include/linux/bpf_lsm.h
    > >
    > > diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
    > > new file mode 100644
    > > index 000000000000..83b96895829f
    > > --- /dev/null
    > > +++ b/include/linux/bpf_lsm.h
    > > @@ -0,0 +1,22 @@
    > > +/* SPDX-License-Identifier: GPL-2.0 */
    > > +
    > > +/*
    > > + * Copyright (C) 2020 Google LLC.
    > > + */
    > > +
    > > +#ifndef _LINUX_BPF_LSM_H
    > > +#define _LINUX_BPF_LSM_H
    > > +
    > > +#include <linux/bpf.h>
    > > +#include <linux/lsm_hooks.h>
    > > +
    > > +#ifdef CONFIG_BPF_LSM
    > > +
    > > +#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
    > > + RET bpf_lsm_##NAME(__VA_ARGS__);
    > > +#include <linux/lsm_hook_defs.h>
    > > +#undef LSM_HOOK
    > > +
    > > +#endif /* CONFIG_BPF_LSM */
    > > +
    > > +#endif /* _LINUX_BPF_LSM_H */
    > > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
    > > index 82875039ca90..1210a819ca52 100644
    > > --- a/kernel/bpf/bpf_lsm.c
    > > +++ b/kernel/bpf/bpf_lsm.c
    > > @@ -7,6 +7,20 @@
    > > #include <linux/filter.h>
    > > #include <linux/bpf.h>
    > > #include <linux/btf.h>
    > > +#include <linux/lsm_hooks.h>
    > > +#include <linux/bpf_lsm.h>
    > > +
    > > +/* For every LSM hook that allows attachment of BPF programs, declare a nop
    > > + * function where a BPF program can be attached.
    > > + */
    > > +#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
    > > +noinline __weak RET bpf_lsm_##NAME(__VA_ARGS__) \
    >
    > I don't think the __weak is needed any more here?

    This was suggested in:

    https://lore.kernel.org/bpf/20200221022537.wbmhdfkdbfvw2pww@ast-mbp/

    "I think I saw cases when gcc ignored 'noinline' when function is
    defined in the same file and still performed inlining while keeping
    the function body. To be safe I think __weak is necessary. That will
    guarantee noinline."

    It happened to work nicely with the previous approach for the special
    hooks but the actual reason for adding the __weak was to guarrantee
    that these functions don't get inlined.

    >
    > > +{ \
    > > + return DEFAULT; \
    >
    > I'm impressed that LSM_RET_VOID actually works. :)

    All the credit goes to Andrii :)

    - KP

    >
    > -Kees
    >
    > > +}
    > > +
    > > +#include <linux/lsm_hook_defs.h>
    > > +#undef LSM_HOOK
    > >
    > > const struct bpf_prog_ops lsm_prog_ops = {
    > > };
    > > --
    > > 2.20.1
    > >
    >
    > --
    > Kees Cook

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