filter: added BPF random opcode

Added a new ancillary load (bpf call in eBPF parlance) that produces
a 32-bit random number. We are implementing it as an ancillary load
(instead of an ISA opcode) because (a) it is simpler, (b) allows easy
JITing, and (c) seems more in line with generic ISAs that do not have
"get a random number" as a instruction, but as an OS call.

The main use for this ancillary load is to perform random packet sampling.

Signed-off-by: Chema Gonzalez <chema@google.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 3 insertions, 1 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 024fd03e5d18..759abf78dd61 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -223,6 +223,7 @@ enum {
         BPF_S_ANC_VLAN_TAG,
         BPF_S_ANC_VLAN_TAG_PRESENT,
         BPF_S_ANC_PAY_OFFSET,
+        BPF_S_ANC_RANDOM,
 };
 
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 8eb9ccaa5b48..253b4d42cf2b 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -130,7 +130,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_VLAN_TAG 44
 #define SKF_AD_VLAN_TAG_PRESENT 48
 #define SKF_AD_PAY_OFFSET       52
-#define SKF_AD_MAX      56
+#define SKF_AD_RANDOM   56
+#define SKF_AD_MAX      60
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)