[apple/security.git] / OSX / libsecurity_utilities / lib / macho++.cpp

/*
 * Copyright (c) 2006-2014 Apple Inc. All Rights Reserved.
 * 
 * @APPLE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */

//
// macho++ - Mach-O object file helpers
//
#include "macho++.h"
#include <security_utilities/alloc.h>
#include <security_utilities/memutils.h>
#include <security_utilities/endian.h>
#include <mach-o/dyld.h>
#include <list>
#include <algorithm>
#include <iterator>

namespace Security {

/* Maximum number of archs a fat binary can have */
static const int MAX_ARCH_COUNT = 100;
/* Maximum power of 2 that a mach-o can be aligned by */
static const int MAX_ALIGN = 30;

//
// Architecture values
//
Architecture::Architecture(const fat_arch &arch)
        : pair<cpu_type_t, cpu_subtype_t>(arch.cputype, arch.cpusubtype)
{
}

Architecture::Architecture(const char *name)
{
        if (const NXArchInfo *nxa = NXGetArchInfoFromName(name)) {
                this->first = nxa->cputype;
                this->second = nxa->cpusubtype;
        } else {
                this->first = this->second = none;
        }
}


//
// The local architecture.
//
// We take this from ourselves - the architecture of our main program Mach-O binary.
// There's the NXGetLocalArchInfo API, but it insists on saying "i386" on modern
// x86_64-centric systems, and lies to ppc (Rosetta) programs claiming they're native ppc.
// So let's not use that.
//
Architecture Architecture::local()
{
        return MainMachOImage().architecture();
}


//
// Translate between names and numbers
//
const char *Architecture::name() const
{
        if (const NXArchInfo *info = NXGetArchInfoFromCpuType(cpuType(), cpuSubtype()))
                return info->name;
        else
                return NULL;
}

std::string Architecture::displayName() const
{
        if (const char *s = this->name())
                return s;
        char buf[20];
        snprintf(buf, sizeof(buf), "(%d:%d)", cpuType(), cpuSubtype());
        return buf;
}
        

//
// Compare architectures.
// This is asymmetrical; the second argument provides for some templating.
//
bool Architecture::matches(const Architecture &templ) const
{
        if (first != templ.first)
                return false;   // main architecture mismatch
        if (templ.second == CPU_SUBTYPE_MULTIPLE)
                return true;    // subtype wildcard
        // match subtypes, ignoring feature bits
        return ((second ^ templ.second) & ~CPU_SUBTYPE_MASK) == 0;
}


//
// MachOBase contains knowledge of the Mach-O object file format,
// but abstracts from any particular sourcing. It must be subclassed,
// and the subclass must provide the file header and commands area
// during its construction. Memory is owned by the subclass.
//
MachOBase::~MachOBase()
{ /* virtual */ }

// provide the Mach-O file header, somehow
void MachOBase::initHeader(const mach_header *header)
{
        mHeader = header;
        switch (mHeader->magic) {
        case MH_MAGIC:
                mFlip = false;
                m64 = false;
                break;
        case MH_CIGAM:
                mFlip = true;
                m64 = false;
                break;
        case MH_MAGIC_64:
                mFlip = false;
                m64 = true;
                break;
        case MH_CIGAM_64:
                mFlip = true;
                m64 = true;
                break;
        default:
                secinfo("macho", "%p: unrecognized header magic (%x)", this, mHeader->magic);
                UnixError::throwMe(ENOEXEC);
        }
}

// provide the Mach-O commands section, somehow
void MachOBase::initCommands(const load_command *commands)
{
        mCommands = commands;
        mEndCommands = LowLevelMemoryUtilities::increment<load_command>(commands, flip(mHeader->sizeofcmds));
        if (mCommands + 1 > mEndCommands)       // ensure initial load command core available
                UnixError::throwMe(ENOEXEC);
}


size_t MachOBase::headerSize() const
{
        return m64 ? sizeof(mach_header_64) : sizeof(mach_header);
}

size_t MachOBase::commandSize() const
{
        return flip(mHeader->sizeofcmds);
}


//
// Create a MachO object from an open file and a starting offset.
// We load (only) the header and load commands into memory at that time.
// Note that the offset must be relative to the start of the containing file
// (not relative to some intermediate container).
//
MachO::MachO(FileDesc fd, size_t offset, size_t length)
        : FileDesc(fd), mOffset(offset), mLength(length), mSuspicious(false)
{
        if (mOffset == 0)
                mLength = fd.fileSize();
        size_t size = fd.read(&mHeaderBuffer, sizeof(mHeaderBuffer), mOffset);
        if (size != sizeof(mHeaderBuffer))
                UnixError::throwMe(ENOEXEC);
        this->initHeader(&mHeaderBuffer);
        size_t cmdSize = this->commandSize();
        mCommandBuffer = (load_command *)malloc(cmdSize);
        if (!mCommandBuffer)
                UnixError::throwMe();
        if (fd.read(mCommandBuffer, cmdSize, this->headerSize() + mOffset) != cmdSize)
                UnixError::throwMe(ENOEXEC);
        this->initCommands(mCommandBuffer);
        /* If we do not know the length, we cannot do a verification of the mach-o structure */
        if (mLength != 0)
                this->validateStructure();
}

void MachO::validateStructure()
{
        bool isValid = false;

        /* There should be either an LC_SEGMENT, an LC_SEGMENT_64, or an LC_SYMTAB
         load_command and that + size must be equal to the end of the arch */
        for (const struct load_command *cmd = loadCommands(); cmd != NULL; cmd = nextCommand(cmd)) {
                uint32_t cmd_type = flip(cmd->cmd);
                struct segment_command *seg = NULL;
                struct segment_command_64 *seg64 = NULL;
                struct symtab_command *symtab = NULL;

                if (cmd_type ==  LC_SEGMENT) {
                        if(flip(cmd->cmdsize) < sizeof(struct segment_command)) {
                                UnixError::throwMe(ENOEXEC);
                        }
                        seg = (struct segment_command *)cmd;
                        if (strncmp(seg->segname, SEG_LINKEDIT, sizeof(seg->segname)) == 0) {
                                isValid = flip(seg->fileoff) + flip(seg->filesize) == this->length();
                                break;
                        }
                } else if (cmd_type == LC_SEGMENT_64) {
                        if(flip(cmd->cmdsize) < sizeof(struct segment_command_64)) {
                                UnixError::throwMe(ENOEXEC);
                        }
                        seg64 = (struct segment_command_64 *)cmd;
                        if (strncmp(seg64->segname, SEG_LINKEDIT, sizeof(seg64->segname)) == 0) {
                                isValid = flip(seg64->fileoff) + flip(seg64->filesize) == this->length();
                                break;
                        }
                /* PPC binaries have a SYMTAB section */
                } else if (cmd_type == LC_SYMTAB) {
                        if(flip(cmd->cmdsize) < sizeof(struct symtab_command)) {
                                UnixError::throwMe(ENOEXEC);
                        }
                        symtab = (struct symtab_command *)cmd;
                        isValid = flip(symtab->stroff) + flip(symtab->strsize) == this->length();
                        break;
                }
        }

        if (!isValid)
                mSuspicious = true;
}

MachO::~MachO()
{
        ::free(mCommandBuffer);
}


//
// Create a MachO object that is (entirely) mapped into memory.
// The caller must ensire that the underlying mapping persists
// at least as long as our object.
//
MachOImage::MachOImage(const void *address)
{
        this->initHeader((const mach_header *)address);
        this->initCommands(LowLevelMemoryUtilities::increment<const load_command>(address, this->headerSize()));
}


//
// Locate the Mach-O image of the main program
//
MainMachOImage::MainMachOImage()
        : MachOImage(mainImageAddress())
{
}

const void *MainMachOImage::mainImageAddress()
{
        return _dyld_get_image_header(0);
}


//
// Return various header fields
//
Architecture MachOBase::architecture() const
{
        return Architecture(flip(mHeader->cputype), flip(mHeader->cpusubtype));
}

uint32_t MachOBase::type() const
{
        return flip(mHeader->filetype);
}

uint32_t MachOBase::flags() const
{
        return flip(mHeader->flags);
}


//
// Iterate through load commands
//
const load_command *MachOBase::nextCommand(const load_command *command) const
{
        using LowLevelMemoryUtilities::increment;
        /* Do not try and increment by 0, or it will loop forever */
        if (flip(command->cmdsize) == 0)
                UnixError::throwMe(ENOEXEC);
        command = increment<const load_command>(command, flip(command->cmdsize));
        if (command >= mEndCommands)    // end of load commands
                return NULL;
        if (increment(command, sizeof(load_command)) > mEndCommands
                || increment(command, flip(command->cmdsize)) > mEndCommands)
                UnixError::throwMe(ENOEXEC);
        return command;
}


//
// Find a specific load command, by command number.
// If there are multiples, returns the first one found.
//
const load_command *MachOBase::findCommand(uint32_t cmd) const
{
        for (const load_command *command = loadCommands(); command; command = nextCommand(command))
                if (flip(command->cmd) == cmd)
                        return command;
        return NULL;
}


//
// Locate a segment command, by name
//      
const segment_command *MachOBase::findSegment(const char *segname) const
{
        for (const load_command *command = loadCommands(); command; command = nextCommand(command)) {
                switch (flip(command->cmd)) {
                case LC_SEGMENT:
                case LC_SEGMENT_64:
                        {
                                if(flip(command->cmdsize) < sizeof(struct segment_command)) {
                                        UnixError::throwMe(ENOEXEC);
                                }
                                const segment_command *seg = reinterpret_cast<const segment_command *>(command);
                                if (!strncmp(seg->segname, segname, sizeof(seg->segname)))
                                        return seg;
                                break;
                        }
                default:
                        break;
                }
        }
        return NULL;
}

const section *MachOBase::findSection(const char *segname, const char *sectname) const
{
        using LowLevelMemoryUtilities::increment;
        if (const segment_command *seg = findSegment(segname)) {
                if (is64()) {
                        if(flip(seg->cmdsize) < sizeof(segment_command_64)) {
                                UnixError::throwMe(ENOEXEC);
                        }
                        const segment_command_64 *seg64 = reinterpret_cast<const segment_command_64 *>(seg);
                        if (sizeof(*seg64) + (seg64->nsects * sizeof(section_64)) > flip(seg64->cmdsize))               // too many segments; doesn't fit (malformed Mach-O)
                                return NULL;    
                        const section_64 *sect = increment<const section_64>(seg64 + 1, 0);
                        for (unsigned n = flip(seg64->nsects); n > 0; n--, sect++) {
                                if (!strncmp(sect->sectname, sectname, sizeof(sect->sectname)))
                                        return reinterpret_cast<const section *>(sect);
                        }
                } else {
                        if (sizeof(*seg) + (seg->nsects * sizeof(section)) > flip(seg->cmdsize))                // too many segments; doesn't fit (malformed Mach-O)
                                return NULL;
                        const section *sect = increment<const section>(seg + 1, 0);
                        for (unsigned n = flip(seg->nsects); n > 0; n--, sect++) {
                                if (!strncmp(sect->sectname, sectname, sizeof(sect->sectname)))
                                        return sect;
                        }
                }
        }
        return NULL;
}


//
// Translate a union lc_str into the string it denotes.
// Returns NULL (no exceptions) if the entry is corrupt.
//
const char *MachOBase::string(const load_command *cmd, const lc_str &str) const
{
        size_t offset = flip(str.offset);
        const char *sp = LowLevelMemoryUtilities::increment<const char>(cmd, offset);
        if (offset + strlen(sp) + 1 > flip(cmd->cmdsize))       // corrupt string reference
                return NULL;
        return sp;
}


//
// Figure out where the Code Signing information starts in the Mach-O binary image.
// The code signature is at the end of the file, and identified
// by a specially-named section. So its starting offset is also the end
// of the signable part.
// Note that the offset returned is relative to the start of the Mach-O image.
// Returns zero if not found (usually indicating that the binary was not signed).
//
const linkedit_data_command *MachOBase::findCodeSignature() const
{
        if (const load_command *cmd = findCommand(LC_CODE_SIGNATURE)) {
                if(flip(cmd->cmdsize) < sizeof(linkedit_data_command)) {
                        UnixError::throwMe(ENOEXEC);
                }
                return reinterpret_cast<const linkedit_data_command *>(cmd);
        }
        return NULL;            // not found
}

size_t MachOBase::signingOffset() const
{
        if (const linkedit_data_command *lec = findCodeSignature())
                return flip(lec->dataoff);
        else
                return 0;
}

size_t MachOBase::signingLength() const
{
        if (const linkedit_data_command *lec = findCodeSignature())
                return flip(lec->datasize);
        else
                return 0;
}

const linkedit_data_command *MachOBase::findLibraryDependencies() const
{
        if (const load_command *cmd = findCommand(LC_DYLIB_CODE_SIGN_DRS)) {
                if(flip(cmd->cmdsize) < sizeof(linkedit_data_command)) {
                        UnixError::throwMe(ENOEXEC);
                }
                return reinterpret_cast<const linkedit_data_command *>(cmd);
        }
        return NULL;            // not found
}
        
const version_min_command *MachOBase::findMinVersion() const
{
        for (const load_command *command = loadCommands(); command; command = nextCommand(command))
                switch (flip(command->cmd)) {
                case LC_VERSION_MIN_MACOSX:
                case LC_VERSION_MIN_IPHONEOS:
                case LC_VERSION_MIN_WATCHOS:
                case LC_VERSION_MIN_TVOS:
                        if(flip(command->cmdsize) < sizeof(version_min_command)) {
                                UnixError::throwMe(ENOEXEC);
                        }
                        return reinterpret_cast<const version_min_command *>(command);
                }
        return NULL;
}

const build_version_command *MachOBase::findBuildVersion() const
{
    for (const load_command *command = loadCommands(); command; command = nextCommand(command)) {
        if (flip(command->cmd) == LC_BUILD_VERSION) {
            if(flip(command->cmdsize) < sizeof(build_version_command)) {
                UnixError::throwMe(ENOEXEC);
            }
            
            return reinterpret_cast<const build_version_command *>(command);
        }
    }
    return NULL;
}

bool MachOBase::version(uint32_t *platform, uint32_t *minVersion, uint32_t *sdkVersion) const
{
    const build_version_command *bc = findBuildVersion();
    
    if (bc != NULL) {
        if (platform != NULL) { *platform = flip(bc->platform); }
        if (minVersion != NULL) { *minVersion = flip(bc->minos); }
        if (sdkVersion != NULL) { *sdkVersion = flip(bc->sdk); }
        return true;
    }
    
    const version_min_command *vc = findMinVersion();
    
    if (vc != NULL) {
        uint32_t pf;
        switch (flip(vc->cmd)) {
        case LC_VERSION_MIN_MACOSX:
            pf = PLATFORM_MACOS;
            break;
        case LC_VERSION_MIN_IPHONEOS:
            pf = PLATFORM_IOS;
            break;
        case LC_VERSION_MIN_WATCHOS:
            pf = PLATFORM_WATCHOS;
            break;
        case LC_VERSION_MIN_TVOS:
            pf = PLATFORM_TVOS;
            break;
        default:
            // Old style load command, but we don't know what platform to map to.
            pf = 0;
        }
                
        if (platform != NULL) { *platform = pf; }
        if (minVersion != NULL) { *minVersion = flip(vc->version); }
        if (sdkVersion != NULL) { *sdkVersion = flip(vc->sdk); }
        return true;
    }
    
    return false;
}

//
// Return the signing-limit length for this Mach-O binary image.
// This is the signingOffset if present, or the full length if not.
//
size_t MachO::signingExtent() const
{
        if (size_t offset = signingOffset())
                return offset;
        else
                return length();
}


//
// I/O operations
//
void MachO::seek(size_t offset)
{
        FileDesc::seek(mOffset + offset);
}

CFDataRef MachO::dataAt(size_t offset, size_t size)
{
        CFMallocData buffer(size);
        if (this->read(buffer, size, mOffset + offset) != size)
                UnixError::throwMe();
        return buffer;
}

//
// Fat (aka universal) file wrappers.
// The offset is relative to the start of the containing file.
//
Universal::Universal(FileDesc fd, size_t offset /* = 0 */, size_t length /* = 0 */)
        : FileDesc(fd), mBase(offset), mLength(length), mMachType(0), mSuspicious(false)
{
        union {
                fat_header header;              // if this is a fat file
                mach_header mheader;    // if this is a thin file
        } unionHeader;

        if (fd.read(&unionHeader, sizeof(unionHeader), offset) != sizeof(unionHeader))
                UnixError::throwMe(ENOEXEC);
        switch (unionHeader.header.magic) {
        case FAT_MAGIC:
        case FAT_CIGAM:
                {
                        //
                        // Hack alert.
                        // Under certain circumstances (15001604), mArchCount under-counts the architectures
                        // by one, and special testing is required to validate the extra-curricular entry.
                        // We always read an extra entry; in the situations where this might hit end-of-file,
                        // we are content to fail.
                        //
                        mArchCount = ntohl(unionHeader.header.nfat_arch);

                        if (mArchCount > MAX_ARCH_COUNT)
                                UnixError::throwMe(ENOEXEC);

                        size_t archSize = sizeof(fat_arch) * (mArchCount + 1);
                        mArchList = (fat_arch *)malloc(archSize);
                        if (!mArchList)
                                UnixError::throwMe();
                        if (fd.read(mArchList, archSize, mBase + sizeof(unionHeader.header)) != archSize) {
                                ::free(mArchList);
                                UnixError::throwMe(ENOEXEC);
                        }
                        for (fat_arch *arch = mArchList; arch <= mArchList + mArchCount; arch++) {
                                n2hi(arch->cputype);
                                n2hi(arch->cpusubtype);
                                n2hi(arch->offset);
                                n2hi(arch->size);
                                n2hi(arch->align);
                        }
                        const fat_arch *last_arch = mArchList + mArchCount;
                        if (last_arch->cputype == (CPU_ARCH_ABI64 | CPU_TYPE_ARM)) {
                                mArchCount++;
                        }
                        secinfo("macho", "%p is a fat file with %d architectures",
                                this, mArchCount);

                        /* A Mach-O universal file has padding of no more than "page size"
                         * between the header and slices. This padding must be zeroed out or the file
                           is not valid */
                        std::list<struct fat_arch *> sortedList;
                        for (unsigned i = 0; i < mArchCount; i++)
                                sortedList.push_back(mArchList + i);

                        sortedList.sort(^ bool (const struct fat_arch *arch1, const struct fat_arch *arch2) { return arch1->offset < arch2->offset; });

                        const size_t universalHeaderEnd = mBase + sizeof(unionHeader.header) + (sizeof(fat_arch) * mArchCount);
                        size_t prevHeaderEnd = universalHeaderEnd;
                        size_t prevArchSize = 0, prevArchStart = 0;

                        for (auto iterator = sortedList.begin(); iterator != sortedList.end(); ++iterator) {
                                auto ret = mSizes.insert(std::pair<size_t, size_t>((*iterator)->offset, (*iterator)->size));
                                if (ret.second == false) {
                                        ::free(mArchList);
                                        MacOSError::throwMe(errSecInternalError); // Something is wrong if the same size was encountered twice
                                }

                                size_t gapSize = (*iterator)->offset - prevHeaderEnd;

                                /* The size of the padding after the universal cannot be calculated to a fixed size */
                                if (prevHeaderEnd != universalHeaderEnd) {
                                        if (((*iterator)->align > MAX_ALIGN) || gapSize >= (1 << (*iterator)->align)) {
                                                mSuspicious = true;
                                                break;
                                        }
                                }

                                // validate gap bytes in tasty page-sized chunks
                                CssmAutoPtr<uint8_t> gapBytes(Allocator::standard().malloc<uint8_t>(PAGE_SIZE));
                                size_t off = 0;
                                while (off < gapSize) {
                                        size_t want = min(gapSize - off, (size_t)PAGE_SIZE);
                                        size_t got = fd.read(gapBytes, want, prevHeaderEnd + off);
                                        if (got == 0) {
                                                mSuspicious = true;
                                                break;
                                        }
                                        off += got;
                                        for (size_t x = 0; x < got; x++) {
                                                if (gapBytes[x] != 0) {
                                                        mSuspicious = true;
                                                        break;
                                                }
                                        }
                                        if (mSuspicious)
                                                break;
                                }
                                if (off != gapSize)
                                        mSuspicious = true;
                                if (mSuspicious)
                                        break;

                                prevHeaderEnd = (*iterator)->offset + (*iterator)->size;
                                prevArchSize = (*iterator)->size;
                                prevArchStart = (*iterator)->offset;
                        }

                        /* If there is anything extra at the end of the file, reject this */
                        if (!mSuspicious && (prevArchStart + prevArchSize != fd.fileSize()))
                                mSuspicious = true;

                        break;
                }
        case MH_MAGIC:
        case MH_MAGIC_64:
                mArchList = NULL;
                mArchCount = 0;
                mThinArch = Architecture(unionHeader.mheader.cputype, unionHeader.mheader.cpusubtype);
                secinfo("macho", "%p is a thin file (%s)", this, mThinArch.name());
                break;
        case MH_CIGAM:
        case MH_CIGAM_64:
                mArchList = NULL;
                mArchCount = 0;
                mThinArch = Architecture(flip(unionHeader.mheader.cputype), flip(unionHeader.mheader.cpusubtype));
                secinfo("macho", "%p is a thin file (%s)", this, mThinArch.name());
                break;
        default:
                UnixError::throwMe(ENOEXEC);
        }
}

Universal::~Universal()
{
        ::free(mArchList);
}

size_t Universal::lengthOfSlice(size_t offset) const
{
        auto ret = mSizes.find(offset);
        if (ret == mSizes.end())
                MacOSError::throwMe(errSecInternalError);
        return ret->second;
}

//
// Get the "local" architecture from the fat file
// Throws ENOEXEC if not found.
//
MachO *Universal::architecture() const
{
        if (isUniversal())
                return findImage(bestNativeArch());
        else
                return new MachO(*this, mBase, mLength);
}

size_t Universal::archOffset() const
{
        if (isUniversal())
                return mBase + findArch(bestNativeArch())->offset;
        else
                return mBase;
}


//
// Get the specified architecture from the fat file
// Throws ENOEXEC if not found.
//
MachO *Universal::architecture(const Architecture &arch) const
{
        if (isUniversal())
                return findImage(arch);
        else if (mThinArch.matches(arch))
                return new MachO(*this, mBase);
        else
                UnixError::throwMe(ENOEXEC);
}

size_t Universal::archOffset(const Architecture &arch) const
{
        if (isUniversal())
                return mBase + findArch(arch)->offset;
        else if (mThinArch.matches(arch))
                return 0;
        else
                UnixError::throwMe(ENOEXEC);
}

size_t Universal::archLength(const Architecture &arch) const
{
        if (isUniversal())
                return mBase + findArch(arch)->size;
        else if (mThinArch.matches(arch))
                return this->fileSize();
        else
                UnixError::throwMe(ENOEXEC);
}

//
// Get the architecture at a specified offset from the fat file.
// Throws an exception of the offset does not point at a Mach-O image.
//
MachO *Universal::architecture(size_t offset) const
{
        if (isUniversal())
                return make(new MachO(*this, offset));
        else if (offset == mBase)
                return new MachO(*this);
        else
                UnixError::throwMe(ENOEXEC);
}


//
// Locate an architecture from the fat file's list.
// Throws ENOEXEC if not found.
//
const fat_arch *Universal::findArch(const Architecture &target) const
{
        assert(isUniversal());
        const fat_arch *end = mArchList + mArchCount;
        // exact match
        for (const fat_arch *arch = mArchList; arch < end; ++arch)
                if (arch->cputype == target.cpuType()
                        && arch->cpusubtype == target.cpuSubtype())
                        return arch;
        // match for generic model of main architecture
        for (const fat_arch *arch = mArchList; arch < end; ++arch)
                if (arch->cputype == target.cpuType() && arch->cpusubtype == 0)
                        return arch;
        // match for any subarchitecture of the main architecture (questionable)
        for (const fat_arch *arch = mArchList; arch < end; ++arch)
                if (arch->cputype == target.cpuType())
                        return arch;
        // no match
        UnixError::throwMe(ENOEXEC);    // not found    
}

MachO *Universal::findImage(const Architecture &target) const
{
        const fat_arch *arch = findArch(target);
        return make(new MachO(*this, mBase + arch->offset, arch->size));
}
        
MachO* Universal::make(MachO* macho) const
{
        auto_ptr<MachO> mo(macho);                              // safe resource
        uint32_t type = mo->type();
        if (type == 0)                                                  // not a recognized Mach-O type
                UnixError::throwMe(ENOEXEC);
        if (mMachType && mMachType != type)             // inconsistent members
                UnixError::throwMe(ENOEXEC);
        mMachType = type;                                               // record
        return mo.release();
}


//
// Find the best-matching architecture for this fat file.
// We pick the native architecture if it's available.
// If it contains exactly one architecture, we take that.
// Otherwise, we throw.
//
Architecture Universal::bestNativeArch() const
{
        if (isUniversal()) {
                // ask the NXArch API for our native architecture
                const Architecture native = Architecture::local();
                if (fat_arch *match = NXFindBestFatArch(native.cpuType(), native.cpuSubtype(), mArchList, mArchCount))
                        return *match;
                // if the system can't figure it out, pick (arbitrarily) the first one
                return mArchList[0];
        } else
                return mThinArch;
}

//
// List all architectures from the fat file's list.
//
void Universal::architectures(Architectures &archs) const
{
        if (isUniversal()) {
                for (unsigned n = 0; n < mArchCount; n++)
                        archs.insert(mArchList[n]);
        } else {
                auto_ptr<MachO> macho(architecture());
                archs.insert(macho->architecture());
        }
}

//
// Quickly guess the Mach-O type of a file.
// Returns type zero if the file isn't Mach-O or Universal.
// Always looks at the start of the file, and does not change the file pointer.
//
uint32_t Universal::typeOf(FileDesc fd)
{
        mach_header header;
        int max_tries = 3;
        if (fd.read(&header, sizeof(header), 0) != sizeof(header))
                return 0;
        while (max_tries > 0) {
                switch (header.magic) {
                case MH_MAGIC:
                case MH_MAGIC_64:
                        return header.filetype;
                case MH_CIGAM:
                case MH_CIGAM_64:
                        return flip(header.filetype);
                case FAT_MAGIC:
                case FAT_CIGAM:
                        {
                                const fat_arch *arch1 =
                                        LowLevelMemoryUtilities::increment<fat_arch>(&header, sizeof(fat_header));
                                if (fd.read(&header, sizeof(header), ntohl(arch1->offset)) != sizeof(header))
                                        return 0;
                                max_tries--;
                                continue;
                        }
                default:
                        return 0;
                }
        }
    return 0;
}

//
// Strict validation
//
bool Universal::isSuspicious() const
{
        if (mSuspicious)
                return true;
        Universal::Architectures archList;
        architectures(archList);
        for (Universal::Architectures::const_iterator it = archList.begin(); it != archList.end(); ++it) {
                auto_ptr<MachO> macho(architecture(*it));
                if (macho->isSuspicious())
                        return true;
        }
        return false;
}


} // Security