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    SubjectRe: [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs
    On 20-Feb 18:25, Alexei Starovoitov wrote:
    > On Thu, Feb 20, 2020 at 06:52:45PM +0100, KP Singh wrote:
    > > From: KP Singh <kpsingh@google.com>
    > >
    > > The BPF LSM programs are implemented as fexit trampolines to avoid the
    > > overhead of retpolines. These programs cannot be attached to security_*
    > > wrappers as there are quite a few security_* functions that do more than
    > > just calling the LSM callbacks.
    > >
    > > This was discussed on the lists in:
    > >
    > > https://lore.kernel.org/bpf/20200123152440.28956-1-kpsingh@chromium.org/T/#m068becce588a0cdf01913f368a97aea4c62d8266
    > >
    > > Adding a NOP callback after all the static LSM callbacks are called has
    > > the following benefits:
    > >
    > > - The BPF programs run at the right stage of the security_* wrappers.
    > > - They run after all the static LSM hooks allowed the operation,
    > > therefore cannot allow an action that was already denied.
    > >
    > > There are some hooks which do not call call_int_hooks or
    > > call_void_hooks. It's not possible to call the bpf_lsm_* functions
    > > without checking if there is BPF LSM program attached to these hooks.
    > > This is added further in a subsequent patch. For now, these hooks are
    > > marked as NO_BPF (i.e. attachment of BPF programs is not possible).
    >
    > the commit log doesn't match the code.

    Fixed. Thanks!

    >
    > > +
    > > +/* For every LSM hook that allows attachment of BPF programs, declare a NOP
    > > + * function where a BPF program can be attached as an fexit trampoline.
    > > + */
    > > +#define LSM_HOOK(RET, NAME, ...) LSM_HOOK_##RET(NAME, __VA_ARGS__)
    > > +#define LSM_HOOK_int(NAME, ...) noinline int bpf_lsm_##NAME(__VA_ARGS__) \
    >
    > Did you check generated asm?
    > 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.

    Sure, will change it to __weak.

    >
    > And please reduce your cc next time. It's way too long.

    Will do.

    - KP

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