On Tue, Mar 15, 2022 at 5:44 PM Kui-Feng Lee <kuifeng@xxxxxx> wrote:
>
> Add a bpf_cookie field to attach a cookie to an instance of struct
> bpf_link. The cookie of a bpf_link will be installed when calling the
> associated program to make it available to the program.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 4 ++--
> include/linux/bpf.h | 1 +
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/syscall.c | 11 +++++++----
> kernel/trace/bpf_trace.c | 17 +++++++++++++++++
> tools/include/uapi/linux/bpf.h | 1 +
> tools/lib/bpf/bpf.c | 14 ++++++++++++++
> tools/lib/bpf/bpf.h | 1 +
> tools/lib/bpf/libbpf.map | 1 +
> 9 files changed, 45 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 29775a475513..5fab8530e909 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -1753,8 +1753,8 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
>
> EMIT1(0x52); /* push rdx */
>
> - /* mov rdi, 0 */
> - emit_mov_imm64(&prog, BPF_REG_1, 0, 0);
> + /* mov rdi, cookie */
> + emit_mov_imm64(&prog, BPF_REG_1, (long) l->cookie >> 32, (u32) (long) l->cookie);
why __u64 to long casting? I don't think you need to cast anything at
all, but if you want to make that more explicit than just casting to
(u32) should be fine, no?
>
> /* Prepare struct bpf_trace_run_ctx.
> * sub rsp, sizeof(struct bpf_trace_run_ctx)
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index d20a23953696..9469f9264b4f 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1040,6 +1040,7 @@ struct bpf_link {
> struct bpf_prog *prog;
> struct work_struct work;
> struct hlist_node tramp_hlist;
> + u64 cookie;
I was a bit hesitant about adding tramp_hlist into generic struct
bpf_link, but now with also cookie there I'm even more convinced that
it's not the right thing to do... Some BPF links won't have cookie,
some (like multi-kprobe) will have lots of them.
Should we create struct bpf_tramp_link {} which will have tramp_hlist
and cookie? As for tramp_hlist, we can probably also keep it back in
bpf_prog_aux and just fetch it through link->prog->aux->tramp_hlist in
trampoline code. This might reduce amount of code churn in patch 1.
Thoughts?
> };
>
> struct bpf_link_ops {
[...]
