Merge pull request #464 from BishopFox/ux/generate

Add warning when cross-compiling to targets without a cross-compiler …

client/command/generate/generate.go

@@ -30,6 +30,7 @@ import (
 	"path"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strings"
 
 	"time"
@@ -67,6 +68,10 @@ const (
 	DefaultMaxErrors = 1000
 )
 
+const (
+	crossCompilerInfoURL = "https://github.com/BishopFox/sliver/wiki/Cross-Compiling-Implants"
+)
+
 var (
 	// SupportedCompilerTargets - Supported compiler targets
 	SupportedCompilerTargets = map[string]bool{
@@ -263,17 +268,21 @@ func parseCompileFlags(ctx *grumble.Context, con *console.SliverConsoleClient) *
 	}
 
 	targetOS := strings.ToLower(ctx.Flags.String("os"))
-	arch := strings.ToLower(ctx.Flags.String("arch"))
-	targetOS, arch = getTargets(targetOS, arch, con)
-	if targetOS == "" || arch == "" {
+	targetArch := strings.ToLower(ctx.Flags.String("arch"))
+	targetOS, targetArch = getTargets(targetOS, targetArch, con)
+	if targetOS == "" || targetArch == "" {
 		return nil
 	}
-
 	if len(namedPipeC2) > 0 && targetOS != "windows" {
 		con.PrintErrorf("Named pipe pivoting can only be used in Windows.")
 		return nil
 	}
 
+	// Check to see if we can *probably* build the target binary
+	if !checkBuildTargetCompatibility(configFormat, targetOS, targetArch, con) {
+		return nil
+	}
+
 	var tunIP net.IP
 	if wg := ctx.Flags.String("wg"); wg != "" {
 		uniqueWGIP, err := con.Rpc.GenerateUniqueIP(context.Background(), &commonpb.Empty{})
@@ -287,7 +296,7 @@ func parseCompileFlags(ctx *grumble.Context, con *console.SliverConsoleClient) *
 
 	config := &clientpb.ImplantConfig{
 		GOOS:             targetOS,
-		GOARCH:           arch,
+		GOARCH:           targetArch,
 		Name:             name,
 		Debug:            ctx.Flags.Bool("debug"),
 		Evasion:          ctx.Flags.Bool("evasion"),
@@ -555,3 +564,62 @@ func getLimitsString(config *clientpb.ImplantConfig) string {
 	}
 	return strings.Join(limits, "; ")
 }
+
+func checkBuildTargetCompatibility(format clientpb.OutputFormat, targetOS string, targetArch string, con *console.SliverConsoleClient) bool {
+	if format == clientpb.OutputFormat_EXECUTABLE {
+		return true // We don't need cross-compilers when targeting EXECUTABLE formats
+	}
+
+	compilers, err := con.Rpc.GetCompiler(context.Background(), &commonpb.Empty{})
+	if err != nil {
+		con.PrintWarnf("Failed to check target compatibility: %s\n", err)
+		return true
+	}
+
+	if runtime.GOOS != "windows" && targetOS == "windows" {
+		if !hasCC(targetOS, targetArch, compilers.CrossCompilers) {
+			return warnMissingCrossCompiler(format, targetOS, targetArch, con)
+		}
+	}
+
+	if runtime.GOOS != "darwin" && targetOS == "darwin" {
+		if !hasCC(targetOS, targetArch, compilers.CrossCompilers) {
+			return warnMissingCrossCompiler(format, targetOS, targetArch, con)
+		}
+	}
+
+	if runtime.GOOS != "linux" && targetOS == "linux" {
+		if !hasCC(targetOS, targetArch, compilers.CrossCompilers) {
+			return warnMissingCrossCompiler(format, targetOS, targetArch, con)
+		}
+	}
+
+	return true
+}
+
+func hasCC(targetOS string, targetArch string, crossCompilers []*clientpb.CrossCompiler) bool {
+	for _, cc := range crossCompilers {
+		if cc.GetTargetGOOS() == targetOS && cc.GetTargetGOARCH() == targetArch {
+			return true
+		}
+	}
+	return false
+}
+
+func warnMissingCrossCompiler(format clientpb.OutputFormat, targetOS string, targetArch string, con *console.SliverConsoleClient) bool {
+	con.PrintWarnf("WARNING: Missing cross-compiler for %s on %s/%s\n", nameOfOutputFormat(format), targetOS, targetArch)
+	switch targetOS {
+	case "windows":
+		con.PrintWarnf("The server cannot find an installation of mingw")
+	case "darwin":
+		con.PrintWarnf("The server cannot find an installation of osxcross")
+	case "linux":
+		con.PrintWarnf("The server cannot find an installation of musl-cross")
+	}
+	con.PrintWarnf("For more information please read %s\n", crossCompilerInfoURL)
+
+	confirm := false
+	prompt := &survey.Confirm{Message: "Try to compile anyways (will likely fail)?"}
+	survey.AskOne(prompt, &confirm, nil)
+	return confirm
+}

server/generate/binaries.go

@@ -264,7 +264,7 @@ func SliverShellcode(name string, config *models.ImplantConfig) (string, error)
 	// as the sliver-server.
 	if runtime.GOOS != config.GOOS {
 		buildLog.Infof("Cross-compiling from %s/%s to %s/%s", runtime.GOOS, runtime.GOARCH, config.GOOS, config.GOARCH)
-		cc, cxx = getCrossCompilers(config.GOOS, config.GOARCH)
+		cc, cxx = findCrossCompilers(config.GOOS, config.GOARCH)
 		if cc == "" {
 			return "", fmt.Errorf("CC '%s/%s' not found", config.GOOS, config.GOARCH)
 		}
@@ -333,7 +333,7 @@ func SliverSharedLibrary(name string, config *models.ImplantConfig) (string, err
 	// as the sliver-server.
 	if runtime.GOOS != config.GOOS {
 		buildLog.Infof("Cross-compiling from %s/%s to %s/%s", runtime.GOOS, runtime.GOARCH, config.GOOS, config.GOARCH)
-		cc, cxx = getCrossCompilers(config.GOOS, config.GOARCH)
+		cc, cxx = findCrossCompilers(config.GOOS, config.GOARCH)
 		if cc == "" {
 			return "", fmt.Errorf("CC '%s/%s' not found", config.GOOS, config.GOARCH)
 		}
@@ -691,8 +691,8 @@ func getCrossCompilersFromEnv(targetGoos string, targetGoarch string) (string, s
 	return cc, cxx
 }
 
-func getCrossCompilers(targetGoos string, targetGoarch string) (string, string) {
-	var found bool // meh, ugly
+func findCrossCompilers(targetGoos string, targetGoarch string) (string, string) {
+	var found bool
 
 	// Get CC and CXX from ENV
 	cc, cxx := getCrossCompilersFromEnv(targetGoos, targetGoarch)
@@ -713,9 +713,11 @@ func getCrossCompilers(targetGoos string, targetGoarch string) (string, string)
 	// Check to see if CC and CXX exist
 	if _, err := os.Stat(cc); os.IsNotExist(err) {
 		buildLog.Warnf("CC path '%s' does not exist", cc)
+		cc = "" // Path does not exist
 	}
 	if _, err := os.Stat(cxx); os.IsNotExist(err) {
 		buildLog.Warnf("CXX path '%s' does not exist", cxx)
+		cxx = "" // Path does not exist
 	}
 	buildLog.Infof(" CC = '%s'", cc)
 	buildLog.Infof("CXX = '%s'", cxx)
@@ -752,7 +754,7 @@ func GetCompilerTargets() []*clientpb.CompilerTarget {
 
 		// Cross-compile with the right configuration
 		if runtime.GOOS == LINUX || runtime.GOOS == DARWIN {
-			cc, _ := getCrossCompilers(platform[0], platform[1])
+			cc, _ := findCrossCompilers(platform[0], platform[1])
 			if cc != "" {
 				if runtime.GOOS == DARWIN && platform[0] == LINUX && platform[1] == "386" {
 					continue // Darwin can't target 32-bit Linux, even with a cc/cxx
@@ -806,7 +808,7 @@ func GetCrossCompilers() []*clientpb.CrossCompiler {
 		if runtime.GOOS == platform[0] {
 			continue
 		}
-		cc, cxx := getCrossCompilers(platform[0], platform[1])
+		cc, cxx := findCrossCompilers(platform[0], platform[1])
 		if cc != "" {
 			compilers = append(compilers, &clientpb.CrossCompiler{
 				TargetGOOS:   platform[0],