tracing: allow configuring policy mode via options

Example:

```
apiVersion: cilium.io/v1alpha1
kind: TracingPolicyNamespaced
metadata:
  name: "enforce-test"
  namespace: "pizza"
spec:
  options:
    - name: "policy-mode"
      value: "enforce"
  kprobes:
     ...
```

Signed-off-by: Kornilios Kourtis <kornilios@isovalent.com>

bpf/lib/policy_conf.h

@@ -4,6 +4,7 @@
 #ifndef BPF_POLICYCONF_H__
 #define BPF_POLICYCONF_H__
 
+// NB: values should match the ones defined in go (EnforceMode, MonitorMode)
 enum {
 	POLICY_MODE_ENFORCE = 0,
 	POLICY_MODE_MONITOR = 1,

pkg/sensors/tracing/options.go

@@ -10,6 +10,7 @@ import (
 	"github.com/cilium/tetragon/pkg/k8s/apis/cilium.io/v1alpha1"
 	"github.com/cilium/tetragon/pkg/logger"
 	"github.com/cilium/tetragon/pkg/option"
+	"github.com/cilium/tetragon/pkg/tracingpolicy"
 )
 
 type OverrideMethod int
@@ -18,6 +19,7 @@ const (
 	keyOverrideMethod = "override-method"
 	valFmodRet        = "fmod-ret"
 	valOverrideReturn = "override-return"
+	keyPolicyMode     = "policy-mode"
 )
 
 const (
@@ -42,6 +44,7 @@ type specOptions struct {
 	DisableKprobeMulti bool
 	DisableUprobeMulti bool
 	OverrideMethod     OverrideMethod
+	policyMode         tracingpolicy.Mode
 }
 
 type opt struct {
@@ -79,6 +82,16 @@ var opts = map[string]opt{
 			return nil
 		},
 	},
+	keyPolicyMode: opt{
+		set: func(str string, options *specOptions) (err error) {
+			mode, err := tracingpolicy.ParseMode(str)
+			if err != nil {
+				return err
+			}
+			options.policyMode = mode
+			return nil
+		},
+	},
 }
 
 func getSpecOptions(specs []v1alpha1.OptionSpec) (*specOptions, error) {

pkg/sensors/tracing/policyhandler.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 
+	"github.com/cilium/ebpf"
 	"github.com/cilium/tetragon/pkg/eventhandler"
 	"github.com/cilium/tetragon/pkg/policyfilter"
 	"github.com/cilium/tetragon/pkg/sensors"
@@ -52,11 +53,26 @@ func newPolicyInfo(
 	}, nil
 }
 
+type policyConf struct {
+	mode uint8
+}
+
 func (pi *policyInfo) policyConfMap(prog *program.Program) *program.Map {
 	if pi.policyConf != nil {
 		return program.MapUserFrom(pi.policyConf)
 	}
 	pi.policyConf = program.MapBuilderPolicy("policy_conf", prog)
+	prog.MapLoad = append(prog.MapLoad, &program.MapLoad{
+		Index: 0,
+		Name:  "policy_conf",
+		Load: func(m *ebpf.Map, pinPathPrefix string, index uint32) error {
+			conf := policyConf{
+				mode: uint8(pi.specOpts.policyMode),
+			}
+			key := uint32(0)
+			return m.Update(key, &conf, ebpf.UpdateAny)
+		},
+	})
 	return pi.policyConf
 }
 

pkg/tracingpolicy/mode.go

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Tetragon
+
+package tracingpolicy
+
+import "fmt"
+
+type Mode uint8
+
+const (
+	InvalidMode Mode = Mode(^uint8(0))
+	// NB: values below should match the ones in bpf/lib/policy_conf.h
+	EnforceMode Mode = 0
+	MonitorMode Mode = 1
+)
+
+func ParseMode(s string) (Mode, error) {
+	switch s {
+	case "enforce":
+		return EnforceMode, nil
+	case "monitor":
+		return MonitorMode, nil
+	}
+
+	return InvalidMode, fmt.Errorf("invalid mode: %q", s)
+}