> On Nov 6, 2020, at 2:08 PM, Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> This patch enables the FENTRY/FEXIT/RAW_TP tracing program to use
> the bpf_sk_storage_(get|delete) helper, so those tracing programs
> can access the sk's bpf_local_storage and the later selftest
> will show some examples.
>
> The bpf_sk_storage is currently used in bpf-tcp-cc, tc,
> cg sockops...etc which is running either in softirq or
> task context.
>
> This patch adds bpf_sk_storage_get_tracing_proto and
> bpf_sk_storage_delete_tracing_proto. They will check
> in runtime that the helpers can only be called when serving
> softirq or running in a task context. That should enable
> most common tracing use cases on sk.
>
> During the load time, the new tracing_allowed() function
> will ensure the tracing prog using the bpf_sk_storage_(get|delete)
> helper is not tracing any *sk_storage*() function itself.
> The sk is passed as "void *" when calling into bpf_local_storage.
>
> Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
> ---
> include/net/bpf_sk_storage.h | 2 +
> kernel/trace/bpf_trace.c | 5 +++
> net/core/bpf_sk_storage.c | 73 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 80 insertions(+)
>
> diff --git a/include/net/bpf_sk_storage.h b/include/net/bpf_sk_storage.h
> index 3c516dd07caf..0e85713f56df 100644
> --- a/include/net/bpf_sk_storage.h
> +++ b/include/net/bpf_sk_storage.h
> @@ -20,6 +20,8 @@ void bpf_sk_storage_free(struct sock *sk);
>
> extern const struct bpf_func_proto bpf_sk_storage_get_proto;
> extern const struct bpf_func_proto bpf_sk_storage_delete_proto;
> +extern const struct bpf_func_proto bpf_sk_storage_get_tracing_proto;
> +extern const struct bpf_func_proto bpf_sk_storage_delete_tracing_proto;
>
> struct bpf_local_storage_elem;
> struct bpf_sk_storage_diag;
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index e4515b0f62a8..cfce60ad1cb5 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -16,6 +16,7 @@
> #include <linux/syscalls.h>
> #include <linux/error-injection.h>
> #include <linux/btf_ids.h>
> +#include <net/bpf_sk_storage.h>
>
> #include <uapi/linux/bpf.h>
> #include <uapi/linux/btf.h>
> @@ -1735,6 +1736,10 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_skc_to_tcp_request_sock_proto;
> case BPF_FUNC_skc_to_udp6_sock:
> return &bpf_skc_to_udp6_sock_proto;
> + case BPF_FUNC_sk_storage_get:
> + return &bpf_sk_storage_get_tracing_proto;
> + case BPF_FUNC_sk_storage_delete:
> + return &bpf_sk_storage_delete_tracing_proto;
> #endif
> case BPF_FUNC_seq_printf:
> return prog->expected_attach_type == BPF_TRACE_ITER ?
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index 001eac65e40f..1a41c917e08d 100644
> --- a/net/core/bpf_sk_storage.c
> +++ b/net/core/bpf_sk_storage.c
> @@ -6,6 +6,7 @@
> #include <linux/types.h>
> #include <linux/spinlock.h>
> #include <linux/bpf.h>
> +#include <linux/btf.h>
> #include <linux/btf_ids.h>
> #include <linux/bpf_local_storage.h>
> #include <net/bpf_sk_storage.h>
> @@ -378,6 +379,78 @@ const struct bpf_func_proto bpf_sk_storage_delete_proto = {
> .arg2_type = ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> };
>
> +static bool bpf_sk_storage_tracing_allowed(const struct bpf_prog *prog)
> +{
> + const struct btf *btf_vmlinux;
> + const struct btf_type *t;
> + const char *tname;
> + u32 btf_id;
> +
> + if (prog->aux->dst_prog)
> + return false;
> +
> + /* Ensure the tracing program is not tracing
> + * any *sk_storage*() function and also
> + * use the bpf_sk_storage_(get|delete) helper.
> + */
> + switch (prog->expected_attach_type) {
> + case BPF_TRACE_RAW_TP:
> + /* bpf_sk_storage has no trace point */
> + return true;
> + case BPF_TRACE_FENTRY:
> + case BPF_TRACE_FEXIT:
> + btf_vmlinux = bpf_get_btf_vmlinux();
> + btf_id = prog->aux->attach_btf_id;
> + t = btf_type_by_id(btf_vmlinux, btf_id);
What happens to fentry/fexit attach to other BPF programs? I guess
we should check for t == NULL?
Thanks,
Song
> + tname = btf_name_by_offset(btf_vmlinux, t->name_off);
> + return !strstr(tname, "sk_storage");
> + default:
> + return false;
> + }
> +
> + return false;
> +}
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