Add InitGlobalVariable to support setting global variables in bpf code

libbpfgo.go

@@ -776,6 +776,15 @@ func (b *BPFMap) GetValueReadInto(key unsafe.Pointer, value *[]byte) error {
  return nil
 }
 
+func (b *BPFMap) SetInitialValue(value unsafe.Pointer) error {
+ sz := b.ValueSize()
+ ret := C.bpf_map__set_initial_value(b.bpfMap, value, C.ulong(sz))
+ if ret != 0 {
+ return fmt.Errorf("failed to set inital value for map %s: %w", b.name, syscall.Errno(-ret))
+ }
+ return nil
+}
+
 // BPFMapBatchOpts mirrors the C structure bpf_map_batch_opts.
 type BPFMapBatchOpts struct {
  Sz uint64

selftest/global-variable/Makefile

@@ -0,0 +1 @@
+../common/Makefile

selftest/global-variable/go.mod

@@ -0,0 +1,9 @@
+module github.com/aquasecurity/libbpfgo/selftest/global-variable
+
+go 1.18
+
+require github.com/aquasecurity/libbpfgo v0.2.1-libbpf-0.4.0
+
+require golang.org/x/sys v0.0.0-20210514084401-e8d321eab015 // indirect
+
+replace github.com/aquasecurity/libbpfgo => ../../

selftest/global-variable/go.sum

@@ -0,0 +1,12 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/sys v0.0.0-20210514084401-e8d321eab015 h1:hZR0X1kPW+nwyJ9xRxqZk1vx5RUObAPBdKVvXPDUH/E=
+golang.org/x/sys v0.0.0-20210514084401-e8d321eab015/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

selftest/global-variable/main.bpf.c

@@ -0,0 +1,42 @@
+//+build ignore
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+#ifdef asm_inline
+#undef asm_inline
+#define asm_inline asm
+#endif
+
+struct {
+ __uint(type, BPF_MAP_TYPE_RINGBUF);
+ __uint(max_entries, 1 << 24);
+} events SEC(".maps");
+
+const volatile int foobar SEC(".rodata") = 0;
+const volatile int foo SEC(".rodata.foo") = 0;
+const volatile int bar SEC(".rodata.bar") = 0;
+const volatile int baz SEC(".data.baz") = 0;
+const volatile int qux SEC(".data.qux") = 0;
+
+long ringbuffer_flags = 0;
+
+SEC("kprobe/sys_mmap")
+int kprobe__sys_mmap(struct pt_regs *ctx)
+{
+ int *process;
+
+ // Reserve space on the ringbuffer for the sample
+ process = bpf_ringbuf_reserve(&events, sizeof(int), ringbuffer_flags);
+ if (!process) {
+ return 1;
+ }
+
+ *process = foobar + foo + bar + baz + qux;
+
+ bpf_ringbuf_submit(process, ringbuffer_flags);
+ return 1;
+}
+
+char LICENSE[] SEC("license") = "GPL";
+

selftest/global-variable/main.go

@@ -0,0 +1,77 @@
+package main
+
+import "C"
+import (
+ "encoding/binary"
+ "fmt"
+ "os"
+ "syscall"
+ "time"
+ "unsafe"
+
+ bpf "github.com/aquasecurity/libbpfgo"
+)
+
+func exitWithErr(err error) {
+ fmt.Fprintln(os.Stderr, err)
+ os.Exit(-1)
+}
+
+func initGlobalVariable(bpfModule *bpf.Module, name string, value int) {
+ bmap, err := bpfModule.GetMap(name)
+ if err != nil {
+ exitWithErr(err)
+ }
+ val := C.int(value)
+ if err := bmap.SetInitialValue(unsafe.Pointer(&val)); err != nil {
+ exitWithErr(err)
+ }
+}
+
+func main() {
+ bpfModule, err := bpf.NewModuleFromFile("main.bpf.o")
+ if err != nil {
+ exitWithErr(err)
+ }
+ defer bpfModule.Close()
+
+ initGlobalVariable(bpfModule, ".rodata", 2000)
+ initGlobalVariable(bpfModule, ".rodata.foo", 10)
+ initGlobalVariable(bpfModule, ".rodata.bar", 8)
+ initGlobalVariable(bpfModule, ".data.baz", 2)
+ initGlobalVariable(bpfModule, ".data.qux", 1)
+
+ if err := bpfModule.BPFLoadObject(); err != nil {
+ exitWithErr(err)
+ }
+
+ prog, err := bpfModule.GetProgram("kprobe__sys_mmap")
+ if err != nil {
+ exitWithErr(err)
+ }
+
+ if _, err := prog.AttachKprobe("__x64_sys_mmap"); err != nil {
+ exitWithErr(err)
+ }
+
+ eventsChannel := make(chan []byte)
+ rb, err := bpfModule.InitRingBuf("events", eventsChannel)
+ if err != nil {
+ exitWithErr(err)
+ }
+
+ rb.Start()
+ go func() {
+ time.Sleep(time.Second)
+ syscall.Mmap(999, 999, 999, 1, 1)
+ }()
+
+ b := <-eventsChannel
+ if binary.LittleEndian.Uint32(b) != 2021 {
+ fmt.Fprintf(os.Stderr, "invalid data retrieved: %v\n", b)
+ os.Exit(-1)
+ }
+
+ rb.Stop()
+ rb.Close()
+}

selftest/global-variable/run.sh

@@ -0,0 +1 @@
+../common/run-5.8.sh