/// <summary>
/// This Method is a utility to remove the code-signature (if any)
/// from a MachO AppHost binary.
///
/// The tool assumes the following layout of the executable:
///
/// * MachoHeader (64-bit, executable, not swapped integers)
/// * LoadCommands
/// LC_SEGMENT_64 (__PAGEZERO)
/// LC_SEGMENT_64 (__TEXT)
/// LC_SEGMENT_64 (__DATA)
/// LC_SEGMENT_64 (__LINKEDIT)
/// ...
/// LC_SYMTAB
/// ...
/// LC_CODE_SIGNATURE (last)
///
/// * ... Different Segments ...
///
/// * The __LINKEDIT Segment (last)
/// * ... Different sections ...
/// * SYMTAB
/// * (Some alignment bytes)
/// * The Code-signature
///
/// In order to remove the signature, the method:
/// - Removes (zeros out) the LC_CODE_SIGNATURE command
/// - Adjusts the size and count of the load commands in the header
/// - Truncates the size of the __LINKEDIT segment to the end of SYMTAB
/// - Truncates the apphost file to the end of the __LINKEDIT segment
///
/// </summary>
/// <param name="filePath">Path to the AppHost</param>
/// <returns>
/// True if
/// - The input is a MachO binary, and
/// - It is a signed binary, and
/// - The signature was successfully removed
/// False otherwise
/// </returns>
/// <exception cref="AppHostMachOFormatException">
/// The input is a MachO file, but doesn't match the expect format of the AppHost.
/// </exception>
unsafe public static bool RemoveSignature(string filePath)
{
using (var stream = new FileStream(filePath, FileMode.Open, FileAccess.ReadWrite))
{
uint signatureSize = 0;
using (var mappedFile = MemoryMappedFile.CreateFromFile(stream,
mapName: null,
capacity: 0,
MemoryMappedFileAccess.ReadWrite,
HandleInheritability.None,
leaveOpen: true))
{
using (var accessor = mappedFile.CreateViewAccessor())
{
byte *file = null;
RuntimeHelpers.PrepareConstrainedRegions();
try
{
accessor.SafeMemoryMappedViewHandle.AcquirePointer(ref file);
Verify(file != null, MachOFormatError.MemoryMapAccessFault);
MachHeader *header = (MachHeader *)file;
if (!header->IsValid())
{
// Not a MachO file.
return(false);
}
Verify(header->Is64BitExecutable(), MachOFormatError.Not64BitExe);
file += sizeof(MachHeader);
SegmentCommand64 * linkEdit = null;
SymtabCommand * symtab = null;
LinkEditDataCommand *signature = null;
for (uint i = 0; i < header->ncmds; i++)
{
LoadCommand *command = (LoadCommand *)file;
if (command->cmd == Command.LC_SEGMENT_64)
{
SegmentCommand64 *segment = (SegmentCommand64 *)file;
if (segment->SegName.Equals("__LINKEDIT"))
{
Verify(linkEdit == null, MachOFormatError.DuplicateLinkEdit);
linkEdit = segment;
}
}
else if (command->cmd == Command.LC_SYMTAB)
{
Verify(symtab == null, MachOFormatError.DuplicateSymtab);
symtab = (SymtabCommand *)command;
}
else if (command->cmd == Command.LC_CODE_SIGNATURE)
{
Verify(i == header->ncmds - 1, MachOFormatError.SignCommandNotLast);
signature = (LinkEditDataCommand *)command;
break;
}
file += command->cmdsize;
}
if (signature != null)
{
Verify(linkEdit != null, MachOFormatError.SignNeedsLinkEdit);
Verify(symtab != null, MachOFormatError.SignNeedsSymtab);
var symtabEnd = symtab->stroff + symtab->strsize;
var linkEditEnd = linkEdit->fileoff + linkEdit->filesize;
var signatureEnd = signature->dataoff + signature->datasize;
var fileEnd = (ulong)stream.Length;
Verify(linkEditEnd == fileEnd, MachOFormatError.LinkEditNotLast);
Verify(signatureEnd == fileEnd, MachOFormatError.SignBlobNotLast);
Verify(symtab->symoff > linkEdit->fileoff, MachOFormatError.SymtabNotInLinkEdit);
Verify(signature->dataoff > linkEdit->fileoff, MachOFormatError.SignNotInLinkEdit);
// The signature blob immediately follows the symtab blob,
// except for a few bytes of padding.
Verify(signature->dataoff >= symtabEnd && signature->dataoff - symtabEnd < 32, MachOFormatError.SignBlobNotLast);
// Remove the signature command
header->ncmds--;
header->sizeofcmds -= signature->cmdsize;
Unsafe.InitBlock(signature, 0, signature->cmdsize);
// Remove the signature blob (note for truncation)
signatureSize = (uint)(fileEnd - symtabEnd);
// Adjust the __LINKEDIT segment load command
linkEdit->filesize -= signatureSize;
// codesign --remove-signature doesn't reset the vmsize.
// Setting the vmsize here makes the output bin-equal with the original
// unsigned apphost (and not bin-equal with a signed-unsigned-apphost).
linkEdit->vmsize = linkEdit->filesize;
}
}
finally
{
if (file != null)
{
accessor.SafeMemoryMappedViewHandle.ReleasePointer();
}
}
}
}
if (signatureSize != 0)
{
// The signature was removed, update the file length
stream.SetLength(stream.Length - signatureSize);
return(true);
}
return(false);
}
}
/// <summary>
/// This Method is a utility to adjust the apphost MachO-header
/// to include the bytes added by the single-file bundler at the end of the file.
///
/// The tool assumes the following layout of the executable
///
/// * MachoHeader (64-bit, executable, not swapped integers)
/// * LoadCommands
/// LC_SEGMENT_64 (__PAGEZERO)
/// LC_SEGMENT_64 (__TEXT)
/// LC_SEGMENT_64 (__DATA)
/// LC_SEGMENT_64 (__LINKEDIT)
/// ...
/// LC_SYMTAB
///
/// * ... Different Segments
///
/// * The __LINKEDIT Segment (last)
/// * ... Different sections ...
/// * SYMTAB (last)
///
/// The MAC codesign tool places several restrictions on the layout
/// * The __LINKEDIT segment must be the last one
/// * The __LINKEDIT segment must cover the end of the file
/// * All bytes in the __LINKEDIT segment are used by other linkage commands
/// (ex: symbol/string table, dynamic load information etc)
///
/// In order to circumvent these restrictions, we:
/// * Extend the __LINKEDIT segment to include the bundle-data
/// * Extend the string table to include all the bundle-data
/// (that is, the bundle-data appear as strings to the loader/codesign tool).
///
/// This method has certain limitations:
/// * The bytes for the bundler may be unnecessarily loaded at startup
/// * Tools that process the string table may be confused (?)
/// * The string table size is limited to 4GB. Bundles larger than that size
/// cannot be accomodated by this utility.
///
/// </summary>
/// <param name="filePath">Path to the AppHost</param>
/// <returns>
/// True if
/// - The input is a MachO binary, and
/// - The additional bytes were successfully accomodated within the MachO segments.
/// False otherwise
/// </returns>
/// <exception cref="AppHostMachOFormatException">
/// The input is a MachO file, but doesn't match the expect format of the AppHost.
/// </exception>
public static unsafe bool AdjustHeadersForBundle(string filePath)
{
ulong fileLength = (ulong)new FileInfo(filePath).Length;
using (var mappedFile = MemoryMappedFile.CreateFromFile(filePath))
{
using (var accessor = mappedFile.CreateViewAccessor())
{
byte *file = null;
try
{
accessor.SafeMemoryMappedViewHandle.AcquirePointer(ref file);
Verify(file != null, MachOFormatError.MemoryMapAccessFault);
MachHeader *header = (MachHeader *)file;
if (!header->IsValid())
{
// Not a MachO file.
return(false);
}
Verify(header->Is64BitExecutable(), MachOFormatError.Not64BitExe);
file += sizeof(MachHeader);
SegmentCommand64 * linkEdit = null;
SymtabCommand * symtab = null;
LinkEditDataCommand *signature = null;
for (uint i = 0; i < header->ncmds; i++)
{
LoadCommand *command = (LoadCommand *)file;
if (command->cmd == Command.LC_SEGMENT_64)
{
SegmentCommand64 *segment = (SegmentCommand64 *)file;
if (segment->SegName.Equals("__LINKEDIT"))
{
Verify(linkEdit == null, MachOFormatError.DuplicateLinkEdit);
linkEdit = segment;
}
}
else if (command->cmd == Command.LC_SYMTAB)
{
Verify(symtab == null, MachOFormatError.DuplicateSymtab);
symtab = (SymtabCommand *)command;
}
file += command->cmdsize;
}
Verify(linkEdit != null, MachOFormatError.MissingLinkEdit);
Verify(symtab != null, MachOFormatError.MissingSymtab);
// Update the string table to include bundle-data
ulong newStringTableSize = fileLength - symtab->stroff;
if (newStringTableSize > uint.MaxValue)
{
// Too big, too bad;
return(false);
}
symtab->strsize = (uint)newStringTableSize;
// Update the __LINKEDIT segment to include bundle-data
linkEdit->filesize = fileLength - linkEdit->fileoff;
linkEdit->vmsize = linkEdit->filesize;
}
finally
{
if (file != null)
{
accessor.SafeMemoryMappedViewHandle.ReleasePointer();
}
}
}
}
return(true);
}
