tetragon: Add execve-map-entries option

Adding execve-map-entries option to setup entries of execve_map map.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>

Author: olsajiri

docs/data/tetragon_flags.yaml

@@ -110,6 +110,8 @@ type config struct {
 	EventCacheRetryDelay int
 
 	CompatibilitySyscall64SizeType bool
+
+	ExecveMapEntries string
 }
 
 var (

pkg/option/config.go

@@ -118,6 +118,8 @@ const (
 	KeyEventCacheRetryDelay = "event-cache-retry-delay"
 
 	KeyCompatibilitySyscall64SizeType = "enable-compatibility-syscall64-size-type"
+
+	KeyExecveMapEntries = "execve-map-entries"
 )
 
 type UsernameMetadaCode int
@@ -252,6 +254,7 @@ func ReadAndSetFlags() error {
 
 	Config.CompatibilitySyscall64SizeType = viper.GetBool(KeyCompatibilitySyscall64SizeType)
 
+	Config.ExecveMapEntries = viper.GetString(KeyExecveMapEntries)
 	return nil
 }
 
@@ -419,4 +422,6 @@ func AddFlags(flags *pflag.FlagSet) {
 	flags.Int(KeyEventCacheRetryDelay, defaults.DefaultEventCacheRetryDelay, "Delay in seconds between event cache retries")
 
 	flags.Bool(KeyCompatibilitySyscall64SizeType, false, "syscall64 type will produce output of type size (compatibility flag, will be removed in v1.4)")
+
+	flags.String(KeyExecveMapEntries, "32768", "Set entries for execve_map table (entries/size/max)")
 }

pkg/option/flags.go

@@ -5,20 +5,27 @@ package base
 
 import (
 	"log"
+	"os"
+	"strconv"
+	"strings"
 	"sync"
 	"testing"
+	"unsafe"
 
 	"github.com/cilium/tetragon/pkg/errmetrics"
 	"github.com/cilium/tetragon/pkg/ksyms"
 	"github.com/cilium/tetragon/pkg/logger"
 	"github.com/cilium/tetragon/pkg/mbset"
+	"github.com/cilium/tetragon/pkg/option"
 	"github.com/cilium/tetragon/pkg/sensors"
 	"github.com/cilium/tetragon/pkg/sensors/exec/config"
+	"github.com/cilium/tetragon/pkg/sensors/exec/execvemap"
 	"github.com/cilium/tetragon/pkg/sensors/program"
+	"github.com/cilium/tetragon/pkg/strutils"
 )
 
 const (
-	execveMapMaxEntries = 32768
+	ExecveMapMaxEntries = 32768
 )
 
 var (
@@ -77,6 +84,43 @@ var (
 	ErrMetricsMap = program.MapBuilder(errmetrics.MapName, Execve)
 )
 
+func readThreadsMax(path string) (int64, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return 0, err
+	}
+	str := strings.TrimRight(string(data), "\n")
+	return strconv.ParseInt(str, 10, 32)
+}
+
+func GetExecveMapEntries(str string) int {
+	entry := int(unsafe.Sizeof(execvemap.ExecveValue{}))
+
+	if len(str) == 0 {
+		return ExecveMapMaxEntries
+	}
+	// pure number of entries
+	if val, err := strconv.Atoi(str); err == nil {
+		return val
+	}
+	// follow threads-max entries
+	if str == "max" {
+		if val, err := readThreadsMax("/proc/sys/kernel/threads-max"); err == nil {
+			return int(val)
+		}
+		logger.GetLogger().Warn("Failed to read /proc/sys/kernel/threads-max file, falling back to default")
+		return ExecveMapMaxEntries
+	}
+	// set entries based on size
+	size, err := strutils.ParseSize(str)
+	if err != nil {
+		logger.GetLogger().Warn("Failed to parse --execve-map-max value, falling back to default")
+		return ExecveMapMaxEntries
+	}
+	val := size / entry
+	return val
+}
+
 func setupSensor() {
 	// exit program function
 	ks, err := ksyms.KernelSymbols()
@@ -97,7 +141,13 @@ func setupSensor() {
 	}
 	logger.GetLogger().Infof("Exit probe on %s", Exit.Attach)
 
-	ExecveMap.SetMaxEntries(execveMapMaxEntries)
+	entries := GetExecveMapEntries(option.Config.ExecveMapEntries)
+	ExecveMap.SetMaxEntries(entries)
+
+	logger.GetLogger().
+		WithField("size", strutils.SizeWithSuffix(entries*int(unsafe.Sizeof(execvemap.ExecveValue{})))).
+		WithField("config", option.Config.ExecveMapEntries).
+		Infof("Set execve_map entries %d", entries)
 }
 
 func GetExecveMap() *program.Map {

pkg/sensors/base/base.go

@@ -335,6 +335,15 @@ func writeExecveMap(procs []procs) {
 			panic(err)
 		}
 	}
+
+	entries, ok := base.ExecveMap.GetMaxEntries()
+	if !ok {
+		logger.GetLogger().Warnf("Failed to get number of execve_map entries, using default.")
+		entries = base.ExecveMapMaxEntries
+	}
+	logger.GetLogger().Infof("Maximum execve_map entries %d, need to add %d.", entries, len(procs))
+	i := uint32(0)
+
 	for _, p := range procs {
 		k := &execvemap.ExecveKey{Pid: p.pid}
 		v := &execvemap.ExecveValue{}
@@ -365,6 +374,11 @@ func writeExecveMap(procs []procs) {
 		if err != nil {
 			logger.GetLogger().WithField("value", v).WithError(err).Warn("failed to put value in execve_map")
 		}
+
+		i++
+		if i == entries {
+			break
+		}
 	}
 	// In order for kprobe events from kernel ctx to not abort we need the
 	// execve lookup to map to a valid entry. So to simplify the kernel side
@@ -381,7 +395,7 @@ func writeExecveMap(procs []procs) {
 	})
 	m.Close()
 
-	updateExecveMapStats(int64(len(procs)))
+	updateExecveMapStats(int64(entries))
 }
 
 func pushEvents(ps []procs) {