[btf] Flush kernel spec (BTF) after loading a sensor

[ upstream commit 6f70926 ("[btf] Flush kernel spec (BTF) after
loading a sensor") ]

This patch flushes the BTF when we complete the loading of a sensor.

Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@gmail.com>

pkg/bpf/detect.go

@@ -422,6 +422,10 @@ func HasMissedStatsKprobeMulti() bool {
 }
 
 func LogFeatures() string {
+	// once we have detected all features, flush the BTF spec
+	// we cache all values so calling again a Has* function will
+	// not load the BTF again
+	defer ebtf.FlushKernelSpec()
 	return fmt.Sprintf("override_return: %t, buildid: %t, kprobe_multi: %t, uprobe_multi %t, fmodret: %t, fmodret_syscall: %t, signal: %t, large: %t, link_pin: %t, lsm: %t, missed_stats_kprobe_multi: %t, missed_stats_kprobe: %t",
 		HasOverrideHelper(), HasBuildId(), HasKprobeMulti(), HasUprobeMulti(),
 		HasModifyReturn(), HasModifyReturnSyscall(), HasSignalHelper(), HasProgramLargeSize(),

pkg/sensors/load.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 
 	"github.com/cilium/ebpf"
+	"github.com/cilium/ebpf/btf"
 	cachedbtf "github.com/cilium/tetragon/pkg/btf"
 	"github.com/cilium/tetragon/pkg/kernels"
 	"github.com/cilium/tetragon/pkg/logger"
@@ -115,6 +116,9 @@ func (s *Sensor) Load(bpfDir string) error {
 	progsAdd(s.Progs)
 	AllMaps = append(AllMaps, s.Maps...)
 
+	// cleanup the BTF once we have loaded all sensor's program
+	btf.FlushKernelSpec()
+
 	l.WithField("sensor", s.Name).Infof("Loaded BPF maps and events for sensor successfully")
 	s.Loaded = true
 	return nil

pkg/sensors/program/loader.go

@@ -913,6 +913,11 @@ func doLoadProgram(
 
 	load.Prog = prog
 
+	// in KernelTypes, we use a non-standard BTF which is possibly annotated with symbols
+	// from kernel modules. At this point we don't need that anymore, so we can release
+	// the memory from it.
+	load.KernelTypes = nil
+
 	// Copy the loaded collection before it's destroyed
 	if KeepCollection {
 		return copyLoadedCollection(coll)