Security-55163.44.tar.gz

[apple/security.git] / libsecurity_codesigning / lib / codedirectory.h

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//
// codedirectory - format and operations for code signing "code directory" structures
//
// A CodeDirectory is the top level object describing a particular instance
// of (static) code. It contains hashes of other objects that further describe
// parts of that code; these hashes hold the various pieces together.
//
// This means that if you reliably ascertain the contents of a CodeDirectory,
// you can verify the integrity of the entire code object it represents - the
// CodeDirectory can stand as a proxy for that code.
//
// Code signatures usually use CMS to sign the CodeDirectory to form full
// signature blobs; ad-hoc signatures simply record the SHA-1 hash of the
// CodeDirectory directly. The SHA-1 of the CodeDirectory is also widely
// used as concordance for a particular code instance - in essence, for
// different processes (or a process and the kernel) to "compare notes"
// to make sure they refer to the same code.
//
#ifndef _H_CODEDIRECTORY
#define _H_CODEDIRECTORY

#include <security_utilities/unix++.h>
#include <security_utilities/blob.h>
#include <security_utilities/cfutilities.h>
#include <security_utilities/hashing.h>
#include <Security/CSCommonPriv.h>


namespace Security {
namespace CodeSigning {


//
// Conventional string names for various code signature components.
// Depending on storage, these may end up as filenames, extended attribute names, etc.
//
#define kSecCS_CODEDIRECTORYFILE        "CodeDirectory"         // CodeDirectory
#define kSecCS_SIGNATUREFILE            "CodeSignature"         // CMS Signature
#define kSecCS_REQUIREMENTSFILE         "CodeRequirements"      // internal requirements
#define kSecCS_RESOURCEDIRFILE          "CodeResources"         // resource directory
#define kSecCS_APPLICATIONFILE          "CodeApplication"       // application-specific resource
#define kSecCS_ENTITLEMENTFILE          "CodeEntitlements"      // entitlement configuration


//
// Special hash slot values. In a CodeDirectory, these show up at negative slot
// indices. This enumeration is also used widely in various internal APIs, and as
// type values in embedded SuperBlobs.
//
// How to add a new special slot type:
//      1. Add the new name at the end of the primary or virtual slot array (below).
//      2a. For slots representing existing code pieces, follow the ball for cdInfoSlot.
//      2b. For slots representing global signature components, follow the ball for cdResourceDirSlot.
//      2c. For slots representing per-architecture signature components, follow the ball for cdEntitlementSlot.
// ("Follow the ball" -> Global search for that name and do likewise.)
//
enum {
        //
        // Primary slot numbers.
        // These values are potentially present in the CodeDirectory hash array
        // under their negative values. They are also used in APIs and SuperBlobs.
        // Note that zero must not be used for these (it's page 0 of the main code array),
        // and it is important to assign contiguous (very) small values for them.
        //
        cdInfoSlot = 1,                                         // Info.plist
        cdRequirementsSlot = 2,                         // internal requirements
        cdResourceDirSlot = 3,                          // resource directory
        cdApplicationSlot = 4,                          // Application specific slot
        cdEntitlementSlot = 5,                          // embedded entitlement configuration
        // (add further primary slot numbers here)

        cdSlotCount,                                            // total number of special slots (+1 for slot 0)
        cdSlotMax = cdSlotCount - 1,            // highest special slot number (as a positive number)
        
        //
        // Virtual slot numbers.
        // These values are NOT used in the CodeDirectory hash array. They are used as
        // internal API identifiers and as types in SuperBlobs.
        // Zero is okay to use here; and we assign that to the CodeDirectory itself so
        // it shows up first in (properly sorted) SuperBlob indices. The rest of the
        // numbers is set Far Away so the primary slot set can expand safely.
        // It's okay to have large gaps in these assignments.
        //
        cdCodeDirectorySlot = 0,                        // CodeDirectory
        cdSignatureSlot = 0x10000,                      // CMS signature
        cdIdentificationSlot,                           // identification blob
        // (add further virtual slot numbers here)
};


//
// Special hash slot attributes.
// This is a central description of attributes of each slot.
// Various places in Code Signing pick up those attributes and act accordingly.
//
enum {
        cdComponentPerArchitecture = 1,                 // slot value differs for each Mach-O architecture
        cdComponentIsBlob = 2,                                  // slot value is a Blob (need not be BlobWrapped)
};


//
// A CodeDirectory is a typed Blob describing the secured pieces of a program.
// This structure describes the common header and provides access to the variable-size
// elements packed after it. For help in constructing a CodeDirectory, use the nested
// Builder class.
//
// At the heart of a CodeDirectory lies a packed array of hash digests.
// The array's zero-index element is at offset hashOffset, and the array covers
// elements in the range [-nSpecialSlots .. nCodeSlots-1]. Non-negative indices
// denote pages of the main executable. Negative indices indicate "special" hashes,
// each of a different thing (see cd*Slot constants above).
// Special slots that are in range but not present are zeroed out. Unallocated special
// slots are also presumed absent; this is not an error. (Thus the range of special
// slots can be extended at will.)
//
// HOW TO MANAGE COMPATIBILITY:
// Each CodeDirectory has a format (compatibility) version. Two constants control
// versioning:
//      * currentVersion is the version used for newly created CodeDirectories.
//  * compatibilityLimit is the highest version the code will accept as compatible.
// Test for version < currentVersion to detect old formats that may need special
// handling; this is done in checkIntegrity(). The current code rejects versions
// below earliestVersion.
// Break backward compatibility by rejecting versions that are unsuitable.
// Accept currentVersion < version <= compatibilityLimit as versions newer than
// those understood by this code but engineered (by newer code) to be backward
// compatible. Reject version > compatibilityLimit as incomprehensible gibberish.
//
// When creating a new version, increment currentVersion. When adding new fixed fields,
// just append them; the flex fields will shift to make room. To add new flex fields,
// add a fixed field containing the new field's offset and add suitable computations
// to the Builder to place the new data (right) before the hash array. Remember to check
// for offset in-range in checkIntegrity(). Older code will then simply ignore your
// new fields on load/read.
// Add flag bits to the existing flags field to add features that step outside
// of the linear versioning stream. Leave the 'spare' fields alone unless you need
// something extraordinarily weird - they're meant to be the final escape when everything
// else fails.
// As you create new versions, consider moving the compatibilityLimit out to open up
// new room for backward compatibility.
// To break backward compatibility intentionally, move currentVersion beyond the
// old compatibilityLimit (and move compatibilityLimit further out).
//
class CodeDirectory: public Blob<CodeDirectory, kSecCodeMagicCodeDirectory> {
public:
        Endian<uint32_t> version;               // compatibility version
        Endian<uint32_t> flags;                 // setup and mode flags
        Endian<uint32_t> hashOffset;    // offset of hash slot element at index zero
        Endian<uint32_t> identOffset;   // offset of identifier string
        Endian<uint32_t> nSpecialSlots; // number of special hash slots
        Endian<uint32_t> nCodeSlots;    // number of ordinary (code) hash slots
        Endian<uint32_t> codeLimit;             // limit to main image signature range
        uint8_t hashSize;                               // size of each hash digest (bytes)
        uint8_t hashType;                               // type of hash (kSecCodeSignatureHash* constants)
        uint8_t spare1;                                 // unused (must be zero)
        uint8_t pageSize;                               // log2(page size in bytes); 0 => infinite
        Endian<uint32_t> spare2;                // unused (must be zero)
        Endian<uint32_t> scatterOffset; // offset of optional scatter vector (zero if absent)
        
        // works with the version field; see comments above
        static const uint32_t currentVersion = 0x20100;         // "version 2.1"
        static const uint32_t compatibilityLimit = 0x2F000;     // "version 3 with wiggle room"
        
        static const uint32_t earliestVersion = 0x20001;        // earliest supported version
        static const uint32_t supportsScatter = 0x20100;        // first version to support scatter option
        
        void checkIntegrity() const;    // throws if inconsistent or unsupported version

        typedef uint32_t HashAlgorithm; // types of internal glue hashes
        typedef int Slot;                               // slot index (negative for special slots)
        typedef unsigned int SpecialSlot; // positive special slot index (not for code slots)
        
        const char *identifier() const { return at<const char>(identOffset); }
        char *identifier() { return at<char>(identOffset); }

        // main hash array access
        SpecialSlot maxSpecialSlot() const;
                
        unsigned char *operator [] (Slot slot)
        {
                assert(slot >= int(-nSpecialSlots) && slot < int(nCodeSlots));
                return at<unsigned char>(hashOffset) + hashSize * slot;
        }
        
        const unsigned char *operator [] (Slot slot) const
        {
                assert(slot >= int(-nSpecialSlots) && slot < int(nCodeSlots));
                return at<unsigned char>(hashOffset) + hashSize * slot;
        }
        
        //
        // The main page hash array can be "scattered" across the code file
        // by specifying an array of Scatter elements, terminated with an
        // element whose count field is zero.
        // The scatter vector is optional; if absent, the hash array covers
        // a single contiguous range of pages. CodeDirectory versions below
        // supportsScatter never have scatter vectors (they lack the scatterOffset field).
        // 
        struct Scatter {
                Endian<uint32_t> count;                 // number of pages; zero for sentinel (only)
                Endian<uint32_t> base;                  // first page number
                Endian<uint64_t> targetOffset;  // byte offset in target
                Endian<uint64_t> spare;                 // reserved (must be zero)
        };
        Scatter *scatterVector()        // first scatter vector element (NULL if none)
                { return (version >= supportsScatter && scatterOffset) ? at<Scatter>(scatterOffset) : NULL; }
        const Scatter *scatterVector() const
                { return (version >= supportsScatter && scatterOffset) ? at<const Scatter>(scatterOffset) : NULL; }
        
public:
        bool validateSlot(const void *data, size_t size, Slot slot) const;                      // validate memory buffer against page slot
        bool validateSlot(UnixPlusPlus::FileDesc fd, size_t size, Slot slot) const;     // read and validate file
        bool slotIsPresent(Slot slot) const;
        
        class Builder;

public:
        static DynamicHash *hashFor(HashAlgorithm hashType);            // create a DynamicHash subclass for (hashType) digests
        DynamicHash *getHash() const { return hashFor(this->hashType); } // make one for me
        
protected:
        static size_t generateHash(DynamicHash *hash, UnixPlusPlus::FileDesc fd, Hashing::Byte *digest, size_t limit = 0); // hash to count or end of file
        static size_t generateHash(DynamicHash *hash, const void *data, size_t length, Hashing::Byte *digest); // hash data buffer
        
public:
        //
        // Information about SpecialSlots.
        // This specifies meta-data about slots themselves;
        // it does not work with the contents of hash slots.
        //
        static const char *canonicalSlotName(SpecialSlot slot);
        static unsigned slotAttributes(SpecialSlot slot);
        IFDEBUG(static const char * const debugSlotName[]);
};


}       // CodeSigning
}       // Security


#endif //_H_CODEDIRECTORY