optimize: lower kernel version requirement from 5.6 to 5.2

pkg/ebpf_internal/vdso.go

@@ -0,0 +1,155 @@
+// Copied from https://github.com/cilium/ebpf/blob/v0.10.0/internal/vdso.go
+
+package internal
+
+import (
+	"debug/elf"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"math"
+	"os"
+
+	"github.com/v2rayA/dae/pkg/ebpf_internal/internal/unix"
+)
+
+var (
+	errAuxvNoVDSO = errors.New("no vdso address found in auxv")
+)
+
+// vdsoVersion returns the LINUX_VERSION_CODE embedded in the vDSO library
+// linked into the current process image.
+func vdsoVersion() (uint32, error) {
+	// Read data from the auxiliary vector, which is normally passed directly
+	// to the process. Go does not expose that data, so we must read it from procfs.
+	// https://man7.org/linux/man-pages/man3/getauxval.3.html
+	av, err := os.Open("/proc/self/auxv")
+	if errors.Is(err, unix.EACCES) {
+		return 0, fmt.Errorf("opening auxv: %w (process may not be dumpable due to file capabilities)", err)
+	}
+	if err != nil {
+		return 0, fmt.Errorf("opening auxv: %w", err)
+	}
+	defer av.Close()
+
+	vdsoAddr, err := vdsoMemoryAddress(av)
+	if err != nil {
+		return 0, fmt.Errorf("finding vDSO memory address: %w", err)
+	}
+
+	// Use /proc/self/mem rather than unsafe.Pointer tricks.
+	mem, err := os.Open("/proc/self/mem")
+	if err != nil {
+		return 0, fmt.Errorf("opening mem: %w", err)
+	}
+	defer mem.Close()
+
+	// Open ELF at provided memory address, as offset into /proc/self/mem.
+	c, err := vdsoLinuxVersionCode(io.NewSectionReader(mem, int64(vdsoAddr), math.MaxInt64))
+	if err != nil {
+		return 0, fmt.Errorf("reading linux version code: %w", err)
+	}
+
+	return c, nil
+}
+
+// vdsoMemoryAddress returns the memory address of the vDSO library
+// linked into the current process image. r is an io.Reader into an auxv blob.
+func vdsoMemoryAddress(r io.Reader) (uint64, error) {
+	const (
+		_AT_NULL         = 0  // End of vector
+		_AT_SYSINFO_EHDR = 33 // Offset to vDSO blob in process image
+	)
+
+	// Loop through all tag/value pairs in auxv until we find `AT_SYSINFO_EHDR`,
+	// the address of a page containing the virtual Dynamic Shared Object (vDSO).
+	aux := struct{ Tag, Val uint64 }{}
+	for {
+		if err := binary.Read(r, NativeEndian, &aux); err != nil {
+			return 0, fmt.Errorf("reading auxv entry: %w", err)
+		}
+
+		switch aux.Tag {
+		case _AT_SYSINFO_EHDR:
+			if aux.Val != 0 {
+				return aux.Val, nil
+			}
+			return 0, fmt.Errorf("invalid vDSO address in auxv")
+		// _AT_NULL is always the last tag/val pair in the aux vector
+		// and can be treated like EOF.
+		case _AT_NULL:
+			return 0, errAuxvNoVDSO
+		}
+	}
+}
+
+// format described at https://www.man7.org/linux/man-pages/man5/elf.5.html in section 'Notes (Nhdr)'
+type elfNoteHeader struct {
+	NameSize int32
+	DescSize int32
+	Type     int32
+}
+
+// vdsoLinuxVersionCode returns the LINUX_VERSION_CODE embedded in
+// the ELF notes section of the binary provided by the reader.
+func vdsoLinuxVersionCode(r io.ReaderAt) (uint32, error) {
+	hdr, err := NewSafeELFFile(r)
+	if err != nil {
+		return 0, fmt.Errorf("reading vDSO ELF: %w", err)
+	}
+
+	sections := hdr.SectionsByType(elf.SHT_NOTE)
+	if len(sections) == 0 {
+		return 0, fmt.Errorf("no note section found in vDSO ELF")
+	}
+
+	for _, sec := range sections {
+		sr := sec.Open()
+		var n elfNoteHeader
+
+		// Read notes until we find one named 'Linux'.
+		for {
+			if err := binary.Read(sr, hdr.ByteOrder, &n); err != nil {
+				if errors.Is(err, io.EOF) {
+					// We looked at all the notes in this section
+					break
+				}
+				return 0, fmt.Errorf("reading note header: %w", err)
+			}
+
+			// If a note name is defined, it follows the note header.
+			var name string
+			if n.NameSize > 0 {
+				// Read the note name, aligned to 4 bytes.
+				buf := make([]byte, Align(int(n.NameSize), 4))
+				if err := binary.Read(sr, hdr.ByteOrder, &buf); err != nil {
+					return 0, fmt.Errorf("reading note name: %w", err)
+				}
+
+				// Read nul-terminated string.
+				name = unix.ByteSliceToString(buf[:n.NameSize])
+			}
+
+			// If a note descriptor is defined, it follows the name.
+			// It is possible for a note to have a descriptor but not a name.
+			if n.DescSize > 0 {
+				// LINUX_VERSION_CODE is a uint32 value.
+				if name == "Linux" && n.DescSize == 4 && n.Type == 0 {
+					var version uint32
+					if err := binary.Read(sr, hdr.ByteOrder, &version); err != nil {
+						return 0, fmt.Errorf("reading note descriptor: %w", err)
+					}
+					return version, nil
+				}
+
+				// Discard the note descriptor if it exists but we're not interested in it.
+				if _, err := io.CopyN(io.Discard, sr, int64(Align(int(n.DescSize), 4))); err != nil {
+					return 0, err
+				}
+			}
+		}
+	}
+
+	return 0, fmt.Errorf("no Linux note in ELF")
+}