fix: use custom Talos/kernel version when generating UKI

See siderolabs/image-factory#44

Instead of using constants, use proper Talos version and kernel version
discovered from the image.

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>

internal/pkg/secureboot/uki/generate.go

@@ -19,7 +19,7 @@ import (
 )
 
 func (builder *Builder) generateOSRel() error {
-	osRelease, err := version.OSRelease()
+	osRelease, err := version.OSReleaseFor(version.Name, builder.Version)
 	if err != nil {
 		return err
 	}
@@ -94,9 +94,26 @@ func (builder *Builder) generateSplash() error {
 }
 
 func (builder *Builder) generateUname() error {
+	// it is not always possible to get the kernel version from the kernel image, so we
+	// do a bit of pre-checks
+	var kernelVersion string
+
+	if builder.Version == version.Tag {
+		// if building from the same version of Talos, use default kernel version
+		kernelVersion = constants.DefaultKernelVersion
+	} else {
+		// otherwise, try to get the kernel version from the kernel image
+		kernelVersion, _ = DiscoverKernelVersion(builder.KernelPath) //nolint:errcheck
+	}
+
+	if kernelVersion == "" {
+		// we haven't got the kernel version, skip the uname section
+		return nil
+	}
+
 	path := filepath.Join(builder.scratchDir, "uname")
 
-	if err := os.WriteFile(path, []byte(constants.DefaultKernelVersion), 0o600); err != nil {
+	if err := os.WriteFile(path, []byte(kernelVersion), 0o600); err != nil {
 		return err
 	}
 

internal/pkg/secureboot/uki/kernel.go

@@ -0,0 +1,69 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package uki
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"os"
+	"strings"
+)
+
+// DiscoverKernelVersion reads kernel version from the kernel image.
+//
+// This only works for x86 kernel images.
+//
+// Based on https://www.kernel.org/doc/html/v5.6/x86/boot.html.
+func DiscoverKernelVersion(kernelPath string) (string, error) {
+	f, err := os.Open(kernelPath)
+	if err != nil {
+		return "", err
+	}
+
+	defer f.Close() //nolint:errcheck
+
+	header := make([]byte, 1024)
+
+	_, err = f.Read(header)
+	if err != nil {
+		return "", err
+	}
+
+	// check header magic
+	if string(header[0x202:0x206]) != "HdrS" {
+		return "", fmt.Errorf("invalid kernel image")
+	}
+
+	setupSects := header[0x1f1]
+	versionOffset := binary.LittleEndian.Uint16(header[0x20e:0x210])
+
+	if versionOffset == 0 {
+		return "", fmt.Errorf("no kernel version")
+	}
+
+	if versionOffset > uint16(setupSects)*0x200 {
+		return "", fmt.Errorf("invalid kernel version offset")
+	}
+
+	versionOffset += 0x200
+
+	version := make([]byte, 256)
+
+	_, err = f.ReadAt(version, int64(versionOffset))
+	if err != nil {
+		return "", err
+	}
+
+	idx := bytes.IndexByte(version, 0)
+	if idx == -1 {
+		return "", fmt.Errorf("invalid kernel version")
+	}
+
+	versionString := string(version[:idx])
+	versionString, _, _ = strings.Cut(versionString, " ")
+
+	return versionString, nil
+}

internal/pkg/secureboot/uki/kernel_test.go

@@ -0,0 +1,21 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package uki_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/siderolabs/talos/internal/pkg/secureboot/uki"
+)
+
+func TestKernelVersion(t *testing.T) {
+	version, err := uki.DiscoverKernelVersion("testdata/kernel")
+	require.NoError(t, err)
+
+	assert.Equal(t, "6.1.58-talos", version)
+}

internal/pkg/secureboot/uki/uki.go

@@ -35,6 +35,8 @@ type Builder struct {
 	//
 	// Arch of the UKI file.
 	Arch string
+	// Version of Talos.
+	Version string
 	// Path to the sd-stub.
 	SdStubPath string
 	// Path to the sd-boot.

pkg/imager/imager.go

@@ -302,6 +302,7 @@ func (i *Imager) buildUKI(report *reporter.Reporter) error {
 
 	builder := uki.Builder{
 		Arch:       i.prof.Arch,
+		Version:    i.prof.Version,
 		SdStubPath: i.prof.Input.SDStub.Path,
 		SdBootPath: i.prof.Input.SDBoot.Path,
 		KernelPath: i.prof.Input.Kernel.Path,

pkg/version/osrelease.go

@@ -14,10 +14,7 @@ import (
 
 // OSRelease returns the contents of /etc/os-release.
 func OSRelease() ([]byte, error) {
-	var (
-		v    string
-		tmpl *template.Template
-	)
+	var v string
 
 	switch Tag {
 	case "none":
@@ -26,14 +23,19 @@ func OSRelease() ([]byte, error) {
 		v = Tag
 	}
 
+	return OSReleaseFor(Name, v)
+}
+
+// OSReleaseFor returns the contents of /etc/os-release for a given name and version.
+func OSReleaseFor(name, version string) ([]byte, error) {
 	data := struct {
 		Name    string
 		ID      string
 		Version string
 	}{
-		Name:    Name,
-		ID:      strings.ToLower(Name),
-		Version: v,
+		Name:    name,
+		ID:      strings.ToLower(name),
+		Version: version,
 	}
 
 	tmpl, err := template.New("").Parse(constants.OSReleaseTemplate)

pkg/version/osrelease_test.go

@@ -7,6 +7,7 @@ package version_test
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/siderolabs/talos/pkg/version"
@@ -19,3 +20,16 @@ func TestOSRelease(t *testing.T) {
 	_, err := version.OSRelease()
 	require.NoError(t, err)
 }
+
+func TestOSReleaseFor(t *testing.T) {
+	t.Parallel()
+
+	contents, err := version.OSReleaseFor("Talos", "v1.0.0")
+	require.NoError(t, err)
+
+	assert.Equal(
+		t,
+		"NAME=\"Talos\"\nID=talos\nVERSION_ID=v1.0.0\nPRETTY_NAME=\"Talos (v1.0.0)\"\nHOME_URL=\"https://www.talos.dev/\"\nBUG_REPORT_URL=\"https://github.com/siderolabs/talos/issues\"\nVENDOR_NAME=\"Sidero Labs\"\nVENDOR_URL=\"https://www.siderolabs.com/\"\n", //nolint:lll
+		string(contents),
+	)
+}