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system_linux.go
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system_linux.go
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package internal
import (
"fmt"
"net"
"os"
"unsafe"
"golang.org/x/sys/unix"
"github.com/hf/nsm"
"github.com/hf/nsm/request"
"github.com/milosgajdos/tenus"
)
const (
entropySeedDevice = "/dev/random"
entropySeedSize = 2048
addrLo = "127.0.0.1/8"
ifaceLo = "lo"
)
// configureLoIface assigns an IP address to the loopback interface.
func configureLoIface() error {
l, err := tenus.NewLinkFrom(ifaceLo)
if err != nil {
return err
}
addr, network, err := net.ParseCIDR(addrLo)
if err != nil {
return err
}
if err = l.SetLinkIp(addr, network); err != nil {
return err
}
return l.SetLinkUp()
}
// writeResolvconf creates our resolv.conf and adds a nameserver.
func writeResolvconf() error {
// A Nitro Enclave's /etc/resolv.conf is a symlink to
// /run/resolvconf/resolv.conf. As of 2022-11-21, the /run/ directory
// exists but not its resolvconf/ subdirectory.
dir := "/run/resolvconf/"
file := dir + "resolv.conf"
if err := os.MkdirAll(dir, 0755); err != nil {
return fmt.Errorf("failed to create directories: %w", err)
}
c := "nameserver 1.1.1.1\n"
if err := os.WriteFile(file, []byte(c), 0644); err != nil {
return fmt.Errorf("failed to write file: %w", err)
}
return nil
}
// maybeSeedEntropy obtains cryptographically secure random bytes from the
// Nitro Secure Module (NSM) and uses them to initialize the system's random
// number generator. If we don't do that, our system is going to start with no
// entropy, which means that calls to /dev/(u)random will block.
func maybeSeedEntropy() {
// Abort if we're not in an enclave.
if !inEnclave {
elog.Println("We are not inside an enclave. Not seeding entropy pool.")
return
}
s, err := nsm.OpenDefaultSession()
if err != nil {
elog.Fatal(err)
}
defer func() {
_ = s.Close()
}()
fd, err := os.OpenFile(entropySeedDevice, os.O_WRONLY, os.ModePerm)
if err != nil {
elog.Fatal(err)
}
defer func() {
if err = fd.Close(); err != nil {
elog.Printf("Failed to close %q: %s", entropySeedDevice, err)
}
}()
var written int
for totalWritten := 0; totalWritten < entropySeedSize; {
res, err := s.Send(&request.GetRandom{})
if err != nil {
elog.Fatalf("Failed to communicate with hypervisor: %s", err)
}
if res.GetRandom == nil {
elog.Fatal("no GetRandom part in NSM's response")
}
if len(res.GetRandom.Random) == 0 {
elog.Fatal("got no random bytes from NSM")
}
// Write NSM-provided random bytes to the system's entropy pool to seed
// it.
if written, err = fd.Write(res.GetRandom.Random); err != nil {
elog.Fatal(err)
}
totalWritten += written
// Tell the system to update its entropy count.
if _, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(fd.Fd()),
uintptr(unix.RNDADDTOENTCNT),
uintptr(unsafe.Pointer(&written)),
); errno != 0 {
elog.Printf("Failed to update system's entropy count: %s", errno)
}
}
elog.Println("Initialized the system's entropy pool.")
}