feat: seed the kernel random pool from the TPM

Use the TPM2 feature to provide high-quality random bytes.

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

go.mod

@@ -54,6 +54,7 @@ require (
 	github.com/godbus/dbus/v5 v5.1.0
 	github.com/golang/mock v1.6.0
 	github.com/google/go-cmp v0.5.9
+	github.com/google/go-tpm v0.9.0
 	github.com/google/gopacket v1.1.19
 	github.com/google/nftables v0.1.0
 	github.com/google/uuid v1.3.0

go.sum

@@ -687,6 +687,8 @@ github.com/google/go-cmp v0.5.8/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeN
 github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/go-containerregistry v0.5.1/go.mod h1:Ct15B4yir3PLOP5jsy0GNeYVaIZs/MK/Jz5any1wFW0=
+github.com/google/go-tpm v0.9.0 h1:sQF6YqWMi+SCXpsmS3fd21oPy/vSddwZry4JnmltHVk=
+github.com/google/go-tpm v0.9.0/go.mod h1:FkNVkc6C+IsvDI9Jw1OveJmxGZUUaKxtrpOS47QWKfU=
 github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
 github.com/google/gofuzz v1.1.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
 github.com/google/gofuzz v1.2.0 h1:xRy4A+RhZaiKjJ1bPfwQ8sedCA+YS2YcCHW6ec7JMi0=

internal/app/init/main.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/siderolabs/talos/internal/pkg/mount"
 	"github.com/siderolabs/talos/internal/pkg/mount/switchroot"
+	"github.com/siderolabs/talos/internal/pkg/rng"
 	"github.com/siderolabs/talos/pkg/machinery/constants"
 	"github.com/siderolabs/talos/pkg/machinery/extensions"
 	"github.com/siderolabs/talos/pkg/version"
@@ -51,6 +52,12 @@ func run() (err error) {
 		return err
 	}
 
+	// Seed RNG.
+	if err = rng.TPMSeed(); err != nil {
+		// not making this fatal error
+		log.Printf("failed to seed from the TPM: %s", err)
+	}
+
 	log.Printf("booting Talos %s", version.Tag)
 
 	// Mount the rootfs.

internal/pkg/rng/pool.go

@@ -0,0 +1,41 @@
+// 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 rng
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"strconv"
+
+	"golang.org/x/sys/unix"
+)
+
+// GetPoolSize returns kernel random pool size.
+func GetPoolSize() (int, error) {
+	contents, err := os.ReadFile("/proc/sys/kernel/random/poolsize")
+	if err != nil {
+		return 0, err
+	}
+
+	return strconv.Atoi(string(bytes.TrimSpace(contents)))
+}
+
+// WriteEntropy writes entropy data to the pool.
+func WriteEntropy(data []byte) error {
+	fd, err := os.OpenFile("/dev/urandom", os.O_WRONLY|unix.O_CLOEXEC|unix.O_NOCTTY, 0)
+	if err != nil {
+		return err
+	}
+
+	defer fd.Close() //nolint:errcheck
+
+	_, err = fd.Write(data)
+	if err != nil {
+		return fmt.Errorf("error writing entropy: %w", err)
+	}
+
+	return fd.Close()
+}

internal/pkg/rng/rng.go

@@ -0,0 +1,6 @@
+// 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 rng handles interaction with kernel random number generator.
+package rng

internal/pkg/rng/tpm.go

@@ -0,0 +1,87 @@
+// 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 rng
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	"github.com/google/go-tpm/tpm2"
+	"github.com/google/go-tpm/tpm2/transport"
+)
+
+// TPMSeed seeds the random entropy pool from the TPM.
+//
+//nolint:gocyclo
+func TPMSeed() error {
+	t, err := transport.OpenTPM()
+	if err != nil {
+		if os.IsNotExist(err) {
+			log.Printf("TPM device is not available")
+
+			return nil
+		}
+
+		return fmt.Errorf("error opening TPM device: %w", err)
+	}
+
+	defer t.Close() //nolint:errcheck
+
+	caps, err := tpm2.GetCapability{
+		Capability:    tpm2.TPMCapTPMProperties,
+		Property:      uint32(tpm2.TPMPTManufacturer),
+		PropertyCount: 1,
+	}.Execute(t)
+	if err != nil {
+		return fmt.Errorf("error getting TPM capabilities: %w", err)
+	}
+
+	props, err := caps.CapabilityData.Data.TPMProperties()
+	if err != nil {
+		return fmt.Errorf("error getting properties: %w", err)
+	}
+
+	log.Printf("TPM manufacturer ID: %08x", props.TPMProperty[0].Value)
+
+	poolSize, err := GetPoolSize()
+	if err != nil {
+		return fmt.Errorf("error getting pool size: %w", err)
+	}
+
+	remaining := poolSize
+	start := time.Now()
+
+	for remaining > 0 {
+		chunk := 32 // default to small chunk (size of AES key)
+		if remaining < chunk {
+			chunk = remaining
+		}
+
+		cmd := tpm2.GetRandom{
+			BytesRequested: uint16(chunk),
+		}
+
+		resp, err := cmd.Execute(t)
+		if err != nil {
+			return fmt.Errorf("error getting random data from the TPM: %w", err)
+		}
+
+		if len(resp.RandomBytes.Buffer) == 0 {
+			return fmt.Errorf("received zero random bytes from the TPM: %w", err)
+		}
+
+		if err = WriteEntropy(resp.RandomBytes.Buffer); err != nil {
+			return fmt.Errorf("error writing random pool entropy: %w", err)
+		}
+
+		remaining -= len(resp.RandomBytes.Buffer)
+	}
+
+	log.Printf("seeded random pool with %d bytes from the TPM in %s", poolSize, time.Since(start))
+
+	return nil
+}