This is xnu-8019. See this file in:
/*
 * Copyright (c) 1991-2015 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_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. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * 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_OSREFERENCE_LICENSE_HEADER_END@
 */
#include <sys/param.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <sys/vnode.h>
#include <vm/vm_kern.h>
#include <mach/kern_return.h>
#include <mach/vm_param.h>
#include <kern/cpu_number.h>
#include <mach-o/fat.h>
#include <kern/mach_loader.h>
#include <kern/mach_fat.h>
#include <libkern/OSByteOrder.h>
#include <machine/exec.h>

/**********************************************************************
* Routine:	fatfile_getarch()
*
* Function:	Locate the architecture-dependant contents of a fat
*		file that match this CPU.
*
* Args: header:		A pointer to the fat file header.
*		size:			How large the fat file header is (including fat_arch array)
*		req_cpu_type:	The required cpu type.
*		mask_bits:	Bits to mask from the sub-image type when
*				grading it vs. the req_cpu_type
*		imgp:		Image params
*		archret (out):	Pointer to fat_arch structure to hold
*				the results.
*
* Returns:	KERN_SUCCESS:	Valid architecture found.
*		KERN_FAILURE:	No valid architecture found.
**********************************************************************/
static load_return_t
fatfile_getarch(
	vm_offset_t              data_ptr,
	vm_size_t                data_size,
	cpu_type_t               req_cpu_type,
	cpu_type_t               mask_bits,
	cpu_subtype_t            req_subcpu_type,
	struct image_params      *imgp,
	struct fat_arch          *archret)
{
	load_return_t           lret;
	struct fat_arch         *arch;
	struct fat_arch         *best_arch;
	int                     grade;
	int                     best_grade;
	size_t                  nfat_arch, max_nfat_arch;
	cpu_type_t              testtype;
	cpu_subtype_t           testsubtype;
	cpu_subtype_t           testfeatures;
	struct fat_header       *header;

	if (sizeof(struct fat_header) > data_size) {
		return LOAD_FAILURE;
	}

	header = (struct fat_header *)data_ptr;
	nfat_arch = OSSwapBigToHostInt32(header->nfat_arch);

	max_nfat_arch = (data_size - sizeof(struct fat_header)) / sizeof(struct fat_arch);
	if (nfat_arch > max_nfat_arch) {
		/* nfat_arch would cause us to read off end of buffer */
		return LOAD_BADMACHO;
	}

	/*
	 * Scan the fat_arch's looking for the best one.  */
	best_arch = NULL;
	best_grade = 0;
	arch = (struct fat_arch *) (data_ptr + sizeof(struct fat_header));
	for (; nfat_arch-- > 0; arch++) {
		testtype = OSSwapBigToHostInt32(arch->cputype);
		testsubtype = OSSwapBigToHostInt32(arch->cpusubtype) & ~CPU_SUBTYPE_MASK;
		testfeatures = OSSwapBigToHostInt32(arch->cpusubtype) & CPU_SUBTYPE_MASK;

		/*
		 *	Check to see if right cpu/subcpu type.
		 */
		if (!binary_match(mask_bits, req_cpu_type, req_subcpu_type, testtype, testsubtype)) {
			continue;
		}

		/*
		 *      Get the grade of the cpu subtype
		 */
		grade = grade_binary(testtype, testsubtype, testfeatures, TRUE);

		/*
		 *	Remember it if it's the best we've seen.
		 */
		if (grade > best_grade) {
			best_grade = grade;
			best_arch = arch;
		}
	}

	/* On X86_64, allow 32 bit exec only for simulator binaries.
	 * Failing here without re-running the grading algorithm is safe because i386
	 * has the lowest possible grade value (so there can't be a lower best grade
	 * that would be allowed if this check denied the i386 slice). */
	if (best_arch != NULL &&
	    validate_potential_simulator_binary(OSSwapBigToHostInt32(best_arch->cputype),
	    imgp, OSSwapBigToHostInt32(best_arch->offset),
	    OSSwapBigToHostInt32(best_arch->size)) != LOAD_SUCCESS) {
		best_arch = NULL;
		best_grade = 0;
	}

	/*
	 *	Return our results.
	 */
	if (best_arch == NULL) {
		lret = LOAD_BADARCH;
	} else {
		archret->cputype        =
		    OSSwapBigToHostInt32(best_arch->cputype);
		archret->cpusubtype     =
		    OSSwapBigToHostInt32(best_arch->cpusubtype);
		archret->offset         =
		    OSSwapBigToHostInt32(best_arch->offset);
		archret->size           =
		    OSSwapBigToHostInt32(best_arch->size);
		archret->align          =
		    OSSwapBigToHostInt32(best_arch->align);

		lret = LOAD_SUCCESS;
	}

	/*
	 * Free the memory we allocated and return.
	 */
	return lret;
}

load_return_t
fatfile_getbestarch(
	vm_offset_t             data_ptr,
	vm_size_t               data_size,
	struct image_params     *imgp,
	struct fat_arch *archret,
	__unused bool affinity)
{
	int primary_type = cpu_type();


	/*
	 * Ignore all architectural bits when determining if an image
	 * in a fat file should be skipped or graded.
	 */
	load_return_t ret = fatfile_getarch(data_ptr, data_size, primary_type, CPU_ARCH_MASK, CPU_SUBTYPE_ANY, imgp, archret);
	return ret;
}

load_return_t
fatfile_getbestarch_for_cputype(
	cpu_type_t cputype,
	cpu_subtype_t cpusubtype,
	vm_offset_t data_ptr,
	vm_size_t data_size,
	struct image_params *imgp,
	struct fat_arch *archret)
{
	/*
	 * Scan the fat_arch array for exact matches for this cpu_type_t only
	 */
	return fatfile_getarch(data_ptr, data_size, cputype, 0, cpusubtype, imgp, archret);
}

/**********************************************************************
* Routine:	fatfile_getarch_with_bits()
*
* Function:	Locate the architecture-dependant contents of a fat
*		file that match this CPU.
*
* Args:	vp:		The vnode for the fat file.
*		archbits:	Architecture specific feature bits
*		header:		A pointer to the fat file header.
*		archret (out):	Pointer to fat_arch structure to hold
*				the results.
*
* Returns:	KERN_SUCCESS:	Valid architecture found.
*		KERN_FAILURE:	No valid architecture found.
**********************************************************************/
load_return_t
fatfile_getarch_with_bits(
	integer_t               archbits,
	vm_offset_t             data_ptr,
	vm_size_t               data_size,
	struct fat_arch         *archret)
{
	/*
	 * Scan the fat_arch array for matches with the requested
	 * architectural bits set, and for the current hardware cpu CPU.
	 */
	return fatfile_getarch(data_ptr, data_size, (archbits & CPU_ARCH_MASK) | (cpu_type() & ~CPU_ARCH_MASK), 0, CPU_SUBTYPE_ANY, NULL, archret);
}

/*
 * Validate the fat_header and fat_arch array in memory. We check that:
 *
 * 1) arch count would not exceed the data buffer
 * 2) arch list does not contain duplicate cputype/cpusubtype tuples
 * 3) arch list does not have two overlapping slices. The area
 *    at the front of the file containing the fat headers is implicitly
 *    a range that a slice should also not try to cover
 */
load_return_t
fatfile_validate_fatarches(vm_offset_t data_ptr, vm_size_t data_size)
{
	uint32_t magic;
	size_t nfat_arch, max_nfat_arch, i, j;
	size_t fat_header_size;

	struct fat_arch         *arches;
	struct fat_header       *header;

	if (sizeof(struct fat_header) > data_size) {
		return LOAD_FAILURE;
	}

	header = (struct fat_header *)data_ptr;
	magic = OSSwapBigToHostInt32(header->magic);
	nfat_arch = OSSwapBigToHostInt32(header->nfat_arch);

	if (magic != FAT_MAGIC) {
		/* must be FAT_MAGIC big endian */
		return LOAD_FAILURE;
	}

	max_nfat_arch = (data_size - sizeof(struct fat_header)) / sizeof(struct fat_arch);
	if (nfat_arch > max_nfat_arch) {
		/* nfat_arch would cause us to read off end of buffer */
		return LOAD_BADMACHO;
	}

	/* now that we know the fat_arch list fits in the buffer, how much does it use? */
	fat_header_size = sizeof(struct fat_header) + nfat_arch * sizeof(struct fat_arch);
	arches = (struct fat_arch *)(data_ptr + sizeof(struct fat_header));

	for (i = 0; i < nfat_arch; i++) {
		uint32_t i_begin = OSSwapBigToHostInt32(arches[i].offset);
		uint32_t i_size = OSSwapBigToHostInt32(arches[i].size);
		uint32_t i_cputype = OSSwapBigToHostInt32(arches[i].cputype);
		uint32_t i_cpusubtype = OSSwapBigToHostInt32(arches[i].cpusubtype);

		if (i_begin < fat_header_size) {
			/* slice is trying to claim part of the file used by fat headers themselves */
			return LOAD_BADMACHO;
		}

		if ((UINT32_MAX - i_size) < i_begin) {
			/* start + size would overflow */
			return LOAD_BADMACHO;
		}
		uint32_t i_end = i_begin + i_size;

		for (j = i + 1; j < nfat_arch; j++) {
			uint32_t j_begin = OSSwapBigToHostInt32(arches[j].offset);
			uint32_t j_size = OSSwapBigToHostInt32(arches[j].size);
			uint32_t j_cputype = OSSwapBigToHostInt32(arches[j].cputype);
			uint32_t j_cpusubtype = OSSwapBigToHostInt32(arches[j].cpusubtype);

			if ((i_cputype == j_cputype) && (i_cpusubtype == j_cpusubtype)) {
				/* duplicate cputype/cpusubtype, results in ambiguous references */
				return LOAD_BADMACHO;
			}

			if ((UINT32_MAX - j_size) < j_begin) {
				/* start + size would overflow */
				return LOAD_BADMACHO;
			}
			uint32_t j_end = j_begin + j_size;

			if (i_begin <= j_begin) {
				if (i_end <= j_begin) {
					/* I completely precedes J */
				} else {
					/* I started before J, but ends somewhere in or after J */
					return LOAD_BADMACHO;
				}
			} else {
				if (i_begin >= j_end) {
					/* I started after J started but also after J ended */
				} else {
					/* I started after J started but before it ended, so there is overlap */
					return LOAD_BADMACHO;
				}
			}
		}
	}

	return LOAD_SUCCESS;
}