ebpf: add helper for obtaining current processor id

This patch adds the possibility to obtain raw_smp_processor_id() in
eBPF. Currently, this is only possible in classic BPF where commit
da2033c28226 ("filter: add SKF_AD_RXHASH and SKF_AD_CPU") has added
facilities for this.

Perhaps most importantly, this would also allow us to track per CPU
statistics with eBPF maps, or to implement a poor-man's per CPU data
structure through eBPF maps.

Example function proto-type looks like:

  u32 (*smp_processor_id)(void) = (void *)BPF_FUNC_get_smp_processor_id;

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 50bf95e29a96..30bfd331882a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -155,5 +155,6 @@ extern const struct bpf_func_proto bpf_map_update_elem_proto;
 extern const struct bpf_func_proto bpf_map_delete_elem_proto;
 
 extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
+extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
 
 #endif /* _LINUX_BPF_H */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1c2ca2b477c8..de1f63668daf 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -166,6 +166,7 @@ enum bpf_func_id {
         BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
         BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
         BPF_FUNC_get_prandom_u32, /* u32 prandom_u32(void) */
+        BPF_FUNC_get_smp_processor_id, /* u32 raw_smp_processor_id(void) */
         __BPF_FUNC_MAX_ID,
 };
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index c1dbbb5d289b..4139a0f8b558 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -662,6 +662,7 @@ const struct bpf_func_proto bpf_map_update_elem_proto __weak;
 const struct bpf_func_proto bpf_map_delete_elem_proto __weak;
 
 const struct bpf_func_proto bpf_get_prandom_u32_proto __weak;
+const struct bpf_func_proto bpf_get_smp_processor_id_proto __weak;
 
 /* To execute LD_ABS/LD_IND instructions __bpf_prog_run() may call
  * skb_copy_bits(), so provide a weak definition of it for NET-less config.
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 95eb59a045ea..bd7f5988ed9c 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -12,6 +12,7 @@
 #include <linux/bpf.h>
 #include <linux/rcupdate.h>
 #include <linux/random.h>
+#include <linux/smp.h>
 
 /* If kernel subsystem is allowing eBPF programs to call this function,
  * inside its own verifier_ops->get_func_proto() callback it should return
@@ -99,3 +100,14 @@ const struct bpf_func_proto bpf_get_prandom_u32_proto = {
         .gpl_only       = false,
         .ret_type       = RET_INTEGER,
 };
+
+static u64 bpf_get_smp_processor_id(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+        return raw_smp_processor_id();
+}
+
+const struct bpf_func_proto bpf_get_smp_processor_id_proto = {
+        .func           = bpf_get_smp_processor_id,
+        .gpl_only       = false,
+        .ret_type       = RET_INTEGER,
+};
diff --git a/net/core/filter.c b/net/core/filter.c
index 4344db39af2e..33310eee6134 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1141,6 +1141,8 @@ sk_filter_func_proto(enum bpf_func_id func_id)
                 return &bpf_map_delete_elem_proto;
         case BPF_FUNC_get_prandom_u32:
                 return &bpf_get_prandom_u32_proto;
+        case BPF_FUNC_get_smp_processor_id:
+                return &bpf_get_smp_processor_id_proto;
         default:
                 return NULL;
         }