Re: [PATCH bpf-next v5 4/7] bpf: lsm: Implement attach, detach and execution

KP Singh
2020-03-23T19:44:37Z

On 23-Mär 12:16, Yonghong Song wrote:
>
>
> On 3/23/20 9:44 AM, KP Singh wrote:
> > From: KP Singh <kpsingh@google.com>
> >
> > JITed BPF programs are dynamically attached to the LSM hooks
> > using BPF trampolines. The trampoline prologue generates code to handle
> > conversion of the signature of the hook to the appropriate BPF context.
> >
> > The allocated trampoline programs are attached to the nop functions
> > initialized as LSM hooks.
> >
> > BPF_PROG_TYPE_LSM programs must have a GPL compatible license and
> > and need CAP_SYS_ADMIN (required for loading eBPF programs).
> >
> > Upon attachment:
> >
> > * A BPF fexit trampoline is used for LSM hooks with a void return type.
> > * A BPF fmod_ret trampoline is used for LSM hooks which return an
> > int. The attached programs can override the return value of the
> > bpf LSM hook to indicate a MAC Policy decision.
> >
> > Signed-off-by: KP Singh <kpsingh@google.com>
> > Reviewed-by: Brendan Jackman <jackmanb@google.com>
> > Reviewed-by: Florent Revest <revest@google.com>
> > ---
> > include/linux/bpf.h | 4 ++++
> > include/linux/bpf_lsm.h | 11 +++++++++++
> > kernel/bpf/bpf_lsm.c | 29 +++++++++++++++++++++++++++++
> > kernel/bpf/btf.c | 9 ++++++++-
> > kernel/bpf/syscall.c | 26 ++++++++++++++++++++++----
> > kernel/bpf/trampoline.c | 17 +++++++++++++----
> > kernel/bpf/verifier.c | 19 +++++++++++++++----
> > 7 files changed, 102 insertions(+), 13 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index af81ec7b783c..adf2e5a6de4b 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -433,6 +433,10 @@ struct btf_func_model {
> > * programs only. Should not be used with normal calls and indirect calls.
> > */
> > #define BPF_TRAMP_F_SKIP_FRAME BIT(2)
> > +/* Override the return value of the original function. This flag only makes
> > + * sense for fexit trampolines.
> > + */
> > +#define BPF_TRAMP_F_OVERRIDE_RETURN BIT(3)
>
> Whether the return value is overridable is determined by hook return type as
> below. Do we still need this flag?

Apologies, this is a relic and should not have been there, will send a
new revision with this removed.

- KP

>
> > /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
> > * bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2
> …