On Mon, Apr 22, 2024 at 10:48:25AM -0700, Alexei Starovoitov wrote:
> On Mon, Apr 22, 2024 at 5:13 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding support for cookie within the session of kprobe multi
> > entry and return program.
> >
> > The session cookie is u64 value and can be retrieved be new
> > kfunc bpf_session_cookie, which returns pointer to the cookie
> > value. The bpf program can use the pointer to store (on entry)
> > and load (on return) the value.
> >
> > The cookie value is implemented via fprobe feature that allows
> > to share values between entry and return ftrace fprobe callbacks.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > kernel/bpf/verifier.c | 7 +++++++
> > kernel/trace/bpf_trace.c | 19 ++++++++++++++++---
> > 2 files changed, 23 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 68cfd6fc6ad4..baaca451aebc 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -10987,6 +10987,7 @@ enum special_kfunc_type {
> > KF_bpf_percpu_obj_drop_impl,
> > KF_bpf_throw,
> > KF_bpf_iter_css_task_new,
> > + KF_bpf_session_cookie,
> > };
> >
> > BTF_SET_START(special_kfunc_set)
> > @@ -11013,6 +11014,7 @@ BTF_ID(func, bpf_throw)
> > #ifdef CONFIG_CGROUPS
> > BTF_ID(func, bpf_iter_css_task_new)
> > #endif
> > +BTF_ID(func, bpf_session_cookie)
> > BTF_SET_END(special_kfunc_set)
> >
> > BTF_ID_LIST(special_kfunc_list)
> > @@ -11043,6 +11045,7 @@ BTF_ID(func, bpf_iter_css_task_new)
> > #else
> > BTF_ID_UNUSED
> > #endif
> > +BTF_ID(func, bpf_session_cookie)
> >
> > static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
> > {
> > @@ -12409,6 +12412,10 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > * because packet slices are not refcounted (see
> > * dynptr_type_refcounted)
> > */
> > + } else if (meta.func_id == special_kfunc_list[KF_bpf_session_cookie]) {
> > + mark_reg_known_zero(env, regs, BPF_REG_0);
> > + regs[BPF_REG_0].type = PTR_TO_MEM;
> > + regs[BPF_REG_0].mem_size = sizeof(u64);
>
> Are you sure you need this?
>
> } else if (!__btf_type_is_struct(ptr_type)) {
>
> block should have handled it automatically.
yes, but only as read-only memory and we need the bpf program to be able to write
to it
I'll double check that, but AFAICS we can't set r0_size/!r0_rdonly before we reach
that if block, because bpf_session_cookie has no arguments
jirka
>
> > +__bpf_kfunc __u64 *bpf_session_cookie(void)
> > +{
>
> ...
