ipxe/src/image/elf.c

/*
 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

/**
 * @file
 *
 * ELF image format
 *
 * A "pure" ELF image is not a bootable image.  There are various
 * bootable formats based upon ELF (e.g. Multiboot), which share
 * common ELF-related functionality.
 */

#include <errno.h>
#include <elf.h>
#include <ipxe/uaccess.h>
#include <ipxe/segment.h>
#include <ipxe/image.h>
#include <ipxe/elf.h>

typedef Elf32_Ehdr	Elf_Ehdr;
typedef Elf32_Phdr	Elf_Phdr;
typedef Elf32_Off	Elf_Off;
#define ELFCLASS	ELFCLASS32

/**
 * Load ELF segment into memory
 *
 * @v image		ELF file
 * @v phdr		ELF program header
 * @v ehdr		ELF executable header
 * @ret entry		Entry point, if found
 * @ret rc		Return status code
 */
static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
			      Elf_Ehdr *ehdr, physaddr_t *entry ) {
	physaddr_t dest;
	userptr_t buffer;
	unsigned long e_offset;
	int rc;

	/* Do nothing for non-PT_LOAD segments */
	if ( phdr->p_type != PT_LOAD )
		return 0;

	/* Check segment lies within image */
	if ( ( phdr->p_offset + phdr->p_filesz ) > image->len ) {
		DBGC ( image, "ELF %p segment outside image\n", image );
		return -ENOEXEC;
	}

	/* Find start address: use physical address for preference,
	 * fall back to virtual address if no physical address
	 * supplied.
	 */
	dest = phdr->p_paddr;
	if ( ! dest )
		dest = phdr->p_vaddr;
	if ( ! dest ) {
		DBGC ( image, "ELF %p segment loads to physical address 0\n",
		       image );
		return -ENOEXEC;
	}
	buffer = phys_to_user ( dest );

	DBGC ( image, "ELF %p loading segment [%x,%x) to [%x,%x,%x)\n", image,
	       phdr->p_offset, ( phdr->p_offset + phdr->p_filesz ),
	       phdr->p_paddr, ( phdr->p_paddr + phdr->p_filesz ),
	       ( phdr->p_paddr + phdr->p_memsz ) );

	/* Verify and prepare segment */
	if ( ( rc = prep_segment ( buffer, phdr->p_filesz,
				   phdr->p_memsz ) ) != 0 ) {
		DBGC ( image, "ELF %p could not prepare segment: %s\n",
		       image, strerror ( rc ) );
		return rc;
	}

	/* Copy image to segment */
	memcpy_user ( buffer, 0, image->data, phdr->p_offset, phdr->p_filesz );

	/* Set execution address, if it lies within this segment */
	if ( ( e_offset = ( ehdr->e_entry - dest ) ) < phdr->p_filesz ) {
		*entry = ehdr->e_entry;
		DBGC ( image, "ELF %p found physical entry point at %lx\n",
		       image, *entry );
	} else if ( ( e_offset = ( ehdr->e_entry - phdr->p_vaddr ) )
		    < phdr->p_filesz ) {
		if ( ! *entry ) {
			*entry = ( dest + e_offset );
			DBGC ( image, "ELF %p found virtual entry point at %lx"
			       " (virt %lx)\n", image, *entry,
			       ( ( unsigned long ) ehdr->e_entry ) );
		}
	}

	return 0;
}

/**
 * Load ELF image into memory
 *
 * @v image		ELF file
 * @ret entry		Entry point
 * @ret rc		Return status code
 */
int elf_load ( struct image *image, physaddr_t *entry ) {
	static const uint8_t e_ident[] = {
		[EI_MAG0]	= ELFMAG0,
		[EI_MAG1]	= ELFMAG1,
		[EI_MAG2]	= ELFMAG2,
		[EI_MAG3]	= ELFMAG3,
		[EI_CLASS]	= ELFCLASS,
	};
	Elf_Ehdr ehdr;
	Elf_Phdr phdr;
	Elf_Off phoff;
	unsigned int phnum;
	int rc;

	/* Read ELF header */
	copy_from_user ( &ehdr, image->data, 0, sizeof ( ehdr ) );
	if ( memcmp ( &ehdr.e_ident[EI_MAG0], e_ident,
		      sizeof ( e_ident ) ) != 0 ) {
		DBGC ( image, "ELF %p has invalid signature\n", image );
		return -ENOEXEC;
	}

	/* Invalidate entry point */
	*entry = 0;

	/* Read ELF program headers */
	for ( phoff = ehdr.e_phoff , phnum = ehdr.e_phnum ; phnum ;
	      phoff += ehdr.e_phentsize, phnum-- ) {
		if ( phoff > image->len ) {
			DBGC ( image, "ELF %p program header %d outside "
			       "image\n", image, phnum );
			return -ENOEXEC;
		}
		copy_from_user ( &phdr, image->data, phoff, sizeof ( phdr ) );
		if ( ( rc = elf_load_segment ( image, &phdr, &ehdr,
					       entry ) ) != 0 ) {
			return rc;
		}
	}

	/* Check for a valid execution address */
	if ( ! *entry ) {
		DBGC ( image, "ELF %p entry point %lx outside image\n",
		       image, ( ( unsigned long ) ehdr.e_entry ) );
		return -ENOEXEC;
	}

	return 0;
}