elf.c

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/*
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

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

/**
 * Load ELF segment into memory
 *
 * @v image             ELF file
 * @v phdr              ELF program header
 * @v dest              Destination address
 * @ret rc              Return status code
 */
static int elf_load_segment ( struct image *image, const Elf_Phdr *phdr,
                              physaddr_t dest ) {
        void *buffer = phys_to_virt ( dest );
        int rc;

        DBGC ( image, "ELF %s loading segment [%x,%x) to [%lx,%lx,%lx)\n",
               image->name, phdr->p_offset, ( phdr->p_offset + phdr->p_filesz ),
               dest, ( dest + phdr->p_filesz ), ( dest + phdr->p_memsz ) );

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

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

        return 0;
}

/**
 * Process ELF segment
 *
 * @v image             ELF file
 * @v ehdr              ELF executable header
 * @v phdr              ELF program header
 * @v process           Segment processor
 * @ret entry           Entry point, if found
 * @ret max             Maximum used address
 * @ret rc              Return status code
 */
static int elf_segment ( struct image *image, const Elf_Ehdr *ehdr,
                         const Elf_Phdr *phdr,
                         int ( * process ) ( struct image *image,
                                             const Elf_Phdr *phdr,
                                             physaddr_t dest ),
                         physaddr_t *entry, physaddr_t *max ) {
        physaddr_t dest;
        physaddr_t end;
        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 %s segment outside image\n", image->name );
                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 %s segment loads to physical address 0\n",
                       image->name );
                return -ENOEXEC;
        }
        end = ( dest + phdr->p_memsz );

        /* Update maximum used address, if applicable */
        if ( end > *max )
                *max = end;

        /* Process segment */
        if ( ( rc = process ( image, phdr, dest ) ) != 0 )
                return rc;

        /* 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 %s found physical entry point at %lx\n",
                       image->name, *entry );
        } else if ( ( e_offset = ( ehdr->e_entry - phdr->p_vaddr ) )
                    < phdr->p_filesz ) {
                if ( ! *entry ) {
                        *entry = ( dest + e_offset );
                        DBGC ( image, "ELF %s found virtual entry point at %lx"
                               " (virt %lx)\n", image->name, *entry,
                               ( ( unsigned long ) ehdr->e_entry ) );
                }
        }

        return 0;
}

/**
 * Process ELF segments
 *
 * @v image             ELF file
 * @v ehdr              ELF executable header
 * @v process           Segment processor
 * @ret entry           Entry point, if found
 * @ret max             Maximum used address
 * @ret rc              Return status code
 */
int elf_segments ( struct image *image, const Elf_Ehdr *ehdr,
                   int ( * process ) ( struct image *image,
                                       const Elf_Phdr *phdr,
                                       physaddr_t dest ),
                   physaddr_t *entry, physaddr_t *max ) {
        const Elf_Phdr *phdr;
        Elf_Off phoff;
        unsigned int phnum;
        int rc;

        /* Initialise maximum used address */
        *max = 0;

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

        /* Read and process ELF program headers */
        for ( phoff = ehdr->e_phoff , phnum = ehdr->e_phnum ; phnum ;
              phoff += ehdr->e_phentsize, phnum-- ) {
                if ( ( image->len < phoff ) ||
                     ( ( image->len - phoff ) < sizeof ( *phdr ) ) ) {
                        DBGC ( image, "ELF %s program header %d outside "
                               "image\n", image->name, phnum );
                        return -ENOEXEC;
                }
                phdr = ( image->data + phoff );
                if ( ( rc = elf_segment ( image, ehdr, phdr, process,
                                          entry, max ) ) != 0 )
                        return rc;
        }

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

        return 0;
}

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

        /* Read ELF header */
        if ( image->len < sizeof ( *ehdr ) ) {
                DBGC ( image, "ELF %s too short for ELF header\n",
                       image->name );
                return -ENOEXEC;
        }
        ehdr = image->data;
        if ( memcmp ( ehdr->e_ident, e_ident, sizeof ( e_ident ) ) != 0 ) {
                DBGC ( image, "ELF %s has invalid signature\n", image->name );
                return -ENOEXEC;
        }

        /* Load ELF segments into memory */
        if ( ( rc = elf_segments ( image, ehdr, elf_load_segment,
                                   entry, max ) ) != 0 )
                return rc;

        return 0;
}