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Read LINUX_VERSION_CODE from vDSO ELF header instead of uname
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,145 @@ | ||
| package internal | ||
|
|
||
| import ( | ||
| "debug/elf" | ||
| "encoding/binary" | ||
| "errors" | ||
| "fmt" | ||
| "io" | ||
| "math" | ||
| "os" | ||
|
|
||
| "github.com/cilium/ebpf/internal/unix" | ||
| ) | ||
|
|
||
| var ( | ||
| errAuxvNoVDSO = errors.New("no vdso address found in auxv") | ||
| ) | ||
|
|
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| // 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 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 | ||
| } | ||
|
|
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| // 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) | ||
| } | ||
|
|
||
| sec := hdr.SectionByType(elf.SHT_NOTE) | ||
| if sec == nil { | ||
| return 0, fmt.Errorf("no note section found in vDSO ELF") | ||
| } | ||
|
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| sr := sec.Open() | ||
| var n elfNoteHeader | ||
|
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||
| // 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) { | ||
| return 0, fmt.Errorf("no Linux note in ELF") | ||
| } | ||
| 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]) | ||
| } | ||
|
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||
| // 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 | ||
| } | ||
|
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||
| // 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 | ||
| } | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,57 @@ | ||
| package internal | ||
|
|
||
| import ( | ||
| "errors" | ||
| "os" | ||
| "testing" | ||
| ) | ||
|
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||
| func TestAuxvVDSOMemoryAddress(t *testing.T) { | ||
| av, err := os.Open("../testdata/auxv.bin") | ||
| if err != nil { | ||
| t.Fatal(err) | ||
| } | ||
| t.Cleanup(func() { av.Close() }) | ||
|
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| addr, err := vdsoMemoryAddress(av) | ||
| if err != nil { | ||
| t.Fatal(err) | ||
| } | ||
|
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| expected := uint64(0x7ffd377e5000) | ||
| if addr != expected { | ||
| t.Errorf("Expected vDSO memory address %x, got %x", expected, addr) | ||
| } | ||
| } | ||
|
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| func TestAuxvNoVDSO(t *testing.T) { | ||
| // Copy of auxv.bin with the vDSO pointer removed. | ||
| av, err := os.Open("../testdata/auxv_no_vdso.bin") | ||
| if err != nil { | ||
| t.Fatal(err) | ||
| } | ||
| t.Cleanup(func() { av.Close() }) | ||
|
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| _, err = vdsoMemoryAddress(av) | ||
| if want, got := errAuxvNoVDSO, err; !errors.Is(got, want) { | ||
| t.Fatalf("expected error '%v', got: %v", want, got) | ||
| } | ||
| } | ||
|
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| func TestLinuxVersionCodeEmbedded(t *testing.T) { | ||
| vdso, err := os.Open("../testdata/vdso.bin") | ||
| if err != nil { | ||
| t.Fatal(err) | ||
| } | ||
| t.Cleanup(func() { vdso.Close() }) | ||
|
|
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| vc, err := vdsoLinuxVersionCode(vdso) | ||
| if err != nil { | ||
| t.Fatal(err) | ||
| } | ||
|
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| expected := uint32(328828) // 5.4.124 | ||
| if vc != expected { | ||
| t.Errorf("Expected version code %d, got %d", expected, vc) | ||
| } | ||
| } |
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