feat(objc): Detect and reject legacy Objective-C fragile runtime metadata #54

Add runtime detection that distinguishes non-fragile (modern) from
fragile (legacy `__OBJC` segment) Objective-C metadata. All ObjC
parsing APIs now return ErrObjcFragileRuntimeUnsupported when called
on binaries with only legacy metadata, since the existing parser
implements only the modern runtime ABI. Binaries with both legacy and
modern metadata are allowed through to support transition-era builds.

Author: blacktop

README.md

@@ -13,7 +13,7 @@ This package goes beyond the Go's `debug/macho` to:
 - Cover ALL load commands and architectures
 - Provide nice summary string output
 - Allow for creating custom MachO files
-- Parse Objective-C runtime information
+- Parse Objective-C runtime information (non-fragile runtime ABI; legacy `__OBJC` metadata is detected and reported unsupported)
 - Parse Swift runtime information
 - Read/Write code signature information
 - Parse fixup chain information

file.go

@@ -52,6 +52,10 @@ type File struct {
 	swift  map[uint64]any
 	ledata *bytes.Buffer // tmp storage of linkedit data
 
+	objcRuntimeOnce          sync.Once
+	objcHasNonFragileRuntime bool
+	objcHasFragileRuntime    bool
+
 	sharedCacheRelativeSelectorBaseVMAddress uint64 // objc_opt version 16
 	swiftAutoDemangle                        bool
 

objc.go

@@ -15,6 +15,33 @@ import (
 
 var ErrObjcSectionNotFound = errors.New("missing required ObjC section")
 var ErrObjcSectionNEmpty = errors.New("required ObjC section is empty")
+var ErrObjcFragileRuntimeUnsupported = errors.New("objective-c fragile runtime metadata is unsupported")
+
+var legacyObjCSectionNames = map[string]struct{}{
+	"__image_info":     {},
+	"__module_info":    {},
+	"__class":          {},
+	"__meta_class":     {},
+	"__protocol":       {},
+	"__protocol_ext":   {},
+	"__category":       {},
+	"__class_vars":     {},
+	"__instance_vars":  {},
+	"__cls_refs":       {},
+	"__message_refs":   {},
+	"__symbols":        {},
+	"__sel_refs":       {},
+	"__string_object":  {},
+	"__class_names":    {},
+	"__meth_var_names": {},
+	"__meth_var_types": {},
+	"__selector_strs":  {},
+}
+
+func isLegacyObjCSectionName(name string) bool {
+	_, ok := legacyObjCSectionNames[strings.ToLower(name)]
+	return ok
+}
 
 // TODO refactor into a pkg
 
@@ -58,21 +85,43 @@ func (f *File) getCStringWithFallback(addr uint64, label string, allowSwift bool
 	return "", err
 }
 
-// HasObjC returns true if MachO contains a __objc_imageinfo section
-func (f *File) HasObjC() bool {
-	for _, s := range f.Segments() {
-		if strings.HasPrefix(s.Name, "__DATA") {
-			if sec := f.Section(s.Name, "__objc_imageinfo"); sec != nil {
-				return true
+func (f *File) hasObjCNonFragileRuntime() bool {
+	f.detectObjCRuntimeKinds()
+	return f.objcHasNonFragileRuntime
+}
+
+func (f *File) hasObjCFragileRuntime() bool {
+	f.detectObjCRuntimeKinds()
+	return f.objcHasFragileRuntime
+}
+
+func (f *File) detectObjCRuntimeKinds() {
+	f.objcRuntimeOnce.Do(func() {
+		for _, sec := range f.Sections {
+			if strings.HasPrefix(sec.Seg, "__DATA") && strings.HasPrefix(sec.Name, "__objc_") {
+				f.objcHasNonFragileRuntime = true
+			}
+			if strings.EqualFold(sec.Seg, "__OBJC") && isLegacyObjCSectionName(sec.Name) {
+				f.objcHasFragileRuntime = true
+			}
+			if f.objcHasNonFragileRuntime && f.objcHasFragileRuntime {
+				return
 			}
 		}
+	})
+}
+
+func (f *File) ensureObjCNonFragileRuntime(api string) error {
+	f.detectObjCRuntimeKinds()
+	if f.objcHasFragileRuntime && !f.objcHasNonFragileRuntime {
+		return fmt.Errorf("%s requires the Objective-C non-fragile runtime: %w", api, ErrObjcFragileRuntimeUnsupported)
 	}
-	if f.CPU == types.CPUI386 {
-		if sec := f.Section("__OBJC", "__image_info"); sec != nil {
-			return true
-		}
-	}
-	return false
+	return nil
+}
+
+// HasObjC returns true if MachO contains Objective-C metadata.
+func (f *File) HasObjC() bool {
+	return f.hasObjCNonFragileRuntime() || f.hasObjCFragileRuntime()
 }
 
 // HasPlusLoadMethod returns true if MachO contains a __objc_nlclslist or __objc_nlcatlist section
@@ -100,6 +149,9 @@ func (f *File) HasObjCMessageReferences() bool {
 			}
 		}
 	}
+	if sec := f.Section("__OBJC", "__message_refs"); sec != nil {
+		return true
+	}
 	return false
 }
 
@@ -126,7 +178,7 @@ func (f *File) GetObjCToc() objc.Toc {
 			case "__objc_selrefs":
 				oInfo.SelRefs = sec.Size / f.pointerSize()
 			}
-		} else if (f.CPU == types.CPUI386) && strings.EqualFold(sec.Name, "__OBJC") {
+		} else if strings.EqualFold(sec.Seg, "__OBJC") {
 			if strings.EqualFold(sec.Name, "__message_refs") {
 				oInfo.SelRefs += sec.SectionHeader.Size / 4
 			} else if strings.EqualFold(sec.Name, "__class") {
@@ -144,6 +196,10 @@ func (f *File) GetObjCToc() objc.Toc {
 
 // GetObjCImageInfo returns the parsed __objc_imageinfo data
 func (f *File) GetObjCImageInfo() (*objc.ImageInfo, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCImageInfo"); err != nil {
+		return nil, err
+	}
+
 	var imgInfo objc.ImageInfo
 	for _, s := range f.Segments() {
 		if strings.HasPrefix(s.Name, "__DATA") {
@@ -196,6 +252,10 @@ func (f *File) GetObjCClassInfo(vmaddr uint64) (*objc.ClassRO64, error) {
 
 // GetObjCClassNames returns a map of section data virtual memory address to their class names
 func (f *File) GetObjCClassNames() (map[uint64]string, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCClassNames"); err != nil {
+		return nil, err
+	}
+
 	class2vmaddr := make(map[uint64]string)
 
 	if sec := f.Section("__TEXT", "__objc_classname"); sec != nil { // Names for locally implemented classes
@@ -230,6 +290,10 @@ func (f *File) GetObjCClassNames() (map[uint64]string, error) {
 
 // GetObjCMethodNames returns a map of section data virtual memory addresses to their method names
 func (f *File) GetObjCMethodNames() (map[uint64]string, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCMethodNames"); err != nil {
+		return nil, err
+	}
+
 	meth2vmaddr := make(map[uint64]string)
 
 	if sec := f.Section("__TEXT", "__objc_methname"); sec != nil { // Method names for locally implemented methods
@@ -264,6 +328,10 @@ func (f *File) GetObjCMethodNames() (map[uint64]string, error) {
 
 // GetObjCClasses returns an array of Objective-C classes
 func (f *File) GetObjCClasses() ([]objc.Class, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCClasses"); err != nil {
+		return nil, err
+	}
+
 	var classes []objc.Class
 
 	for _, s := range f.Segments() {
@@ -313,6 +381,10 @@ func (f *File) GetObjCClasses() ([]objc.Class, error) {
 
 // GetObjCNonLazyClasses returns an array of Objective-C classes that implement +load
 func (f *File) GetObjCNonLazyClasses() ([]objc.Class, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCNonLazyClasses"); err != nil {
+		return nil, err
+	}
+
 	var classes []objc.Class
 
 	for _, s := range f.Segments() {
@@ -381,6 +453,9 @@ func (f *File) disablePreattachedCategories(vmaddr uint64) (uint64, error) {
 
 // GetObjCClass parses an Objective-C class at a given virtual memory address
 func (f *File) GetObjCClass(vmaddr uint64) (*objc.Class, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCClass"); err != nil {
+		return nil, err
+	}
 
 	if c, ok := f.GetObjC(vmaddr); ok {
 		return c.(*objc.Class), nil
@@ -572,6 +647,9 @@ func (f *File) GetObjCClass(vmaddr uint64) (*objc.Class, error) {
 // TODO: get rid of old GetObjCClass
 // GetObjCClass parses an Objective-C class at a given virtual memory address
 func (f *File) GetObjCClass2(vmaddr uint64) (*objc.Class, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCClass2"); err != nil {
+		return nil, err
+	}
 
 	if c, ok := f.GetObjC(vmaddr); ok {
 		return c.(*objc.Class), nil
@@ -763,6 +841,10 @@ func (f *File) GetObjCClass2(vmaddr uint64) (*objc.Class, error) {
 
 // GetObjCCategories returns an array of Objective-C categories by parsing the __objc_catlist data
 func (f *File) GetObjCCategories() ([]objc.Category, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCCategories"); err != nil {
+		return nil, err
+	}
+
 	var categoryPtr objc.CategoryT
 	var categories []objc.Category
 
@@ -880,6 +962,10 @@ func (f *File) GetObjCCategories() ([]objc.Category, error) {
 
 // GetObjCNonLazyCategories returns an array of Objective-C classes that implement +load
 func (f *File) GetObjCNonLazyCategories() ([]objc.Category, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCNonLazyCategories"); err != nil {
+		return nil, err
+	}
+
 	var cats []objc.Category
 
 	for _, s := range f.Segments() {
@@ -1099,6 +1185,9 @@ func (f *File) getObjcProtocol(vmaddr uint64) (proto *objc.Protocol, err error)
 
 // GetObjCProtocols returns the Objective-C protocols
 func (f *File) GetObjCProtocols() ([]objc.Protocol, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCProtocols"); err != nil {
+		return nil, err
+	}
 
 	var protocols []objc.Protocol
 
@@ -1133,6 +1222,10 @@ func (f *File) GetObjCProtocols() ([]objc.Protocol, error) {
 }
 
 func (f *File) GetObjCMethods(vmaddr uint64) ([]objc.Method, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCMethods"); err != nil {
+		return nil, err
+	}
+
 	if c, ok := f.GetObjC(vmaddr); ok {
 		return c.([]objc.Method), nil
 	}
@@ -1152,6 +1245,10 @@ func (f *File) GetObjCMethods(vmaddr uint64) ([]objc.Method, error) {
 
 // GetObjCMethodLists parses the method lists in the __objc_methlist section
 func (f *File) GetObjCMethodLists() ([]objc.Method, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCMethodLists"); err != nil {
+		return nil, err
+	}
+
 	var methods []objc.Method
 	var methodList objc.MethodList
 	var nextMethodListOffset uint64
@@ -1310,6 +1407,10 @@ func (f *File) forEachObjCMethod(methodListVMAddr uint64, handler func(uint64, o
 
 // GetObjCIvars returns the Objective-C instance variables
 func (f *File) GetObjCIvars(vmaddr uint64) ([]objc.Ivar, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCIvars"); err != nil {
+		return nil, err
+	}
+
 	return f.getObjCIvarsWithSwift(vmaddr, false)
 }
 
@@ -1394,6 +1495,10 @@ func (f *File) getObjCIvarsWithSwift(vmaddr uint64, allowSwift bool) ([]objc.Iva
 
 // GetObjCProperties returns the Objective-C properties
 func (f *File) GetObjCProperties(vmaddr uint64) ([]objc.Property, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCProperties"); err != nil {
+		return nil, err
+	}
+
 	return f.getObjCPropertiesWithSwift(vmaddr, false)
 }
 
@@ -1439,6 +1544,10 @@ func (f *File) getObjCPropertiesWithSwift(vmaddr uint64, allowSwift bool) ([]obj
 
 // GetObjCClassReferences returns a map of classes to their section data virtual memory address
 func (f *File) GetObjCClassReferences() (map[uint64]*objc.Class, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCClassReferences"); err != nil {
+		return nil, err
+	}
+
 	clsRefs := make(map[uint64]*objc.Class)
 
 	for _, s := range f.Segments() {
@@ -1486,6 +1595,10 @@ func (f *File) GetObjCClassReferences() (map[uint64]*objc.Class, error) {
 
 // GetObjCSuperReferences returns a map of super classes to their section data virtual memory address
 func (f *File) GetObjCSuperReferences() (map[uint64]*objc.Class, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCSuperReferences"); err != nil {
+		return nil, err
+	}
+
 	clsRefs := make(map[uint64]*objc.Class)
 
 	for _, s := range f.Segments() {
@@ -1532,6 +1645,10 @@ func (f *File) GetObjCSuperReferences() (map[uint64]*objc.Class, error) {
 
 // GetObjCProtoReferences returns a map of protocol names to their section data virtual memory address
 func (f *File) GetObjCProtoReferences() (map[uint64]*objc.Protocol, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCProtoReferences"); err != nil {
+		return nil, err
+	}
+
 	protRefs := make(map[uint64]*objc.Protocol)
 
 	for _, s := range f.Segments() {
@@ -1569,6 +1686,10 @@ func (f *File) GetObjCProtoReferences() (map[uint64]*objc.Protocol, error) {
 
 // GetObjCSelectorReferences returns a map of selector names to their section data virtual memory address
 func (f *File) GetObjCSelectorReferences() (map[uint64]*objc.Selector, error) {
+	if err := f.ensureObjCNonFragileRuntime("GetObjCSelectorReferences"); err != nil {
+		return nil, err
+	}
+
 	selRefs := make(map[uint64]*objc.Selector)
 
 	for _, s := range f.Segments() {