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., 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 <gpxe/uaccess.h>
#include <gpxe/segment.h>
#include <gpxe/image.h>
#include <gpxe/elf.h>

typedef Elf32_Ehdr      Elf_Ehdr;
typedef Elf32_Phdr      Elf_Phdr;
typedef Elf32_Off       Elf_Off;

/**
 * Load ELF segment into memory
 *
 * @v image             ELF file
 * @v phdr              ELF program header
 * @v ehdr              ELF executable header
 * @ret rc              Return status code
 */
static int elf_load_segment ( struct image *image, Elf_Phdr *phdr,
                              Elf_Ehdr *ehdr ) {
        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 ) {
                image->priv.phys = ehdr->e_entry;
                DBGC ( image, "ELF %p found physical entry point at %lx\n",
                       image, image->priv.phys );
        } else if ( ( e_offset = ( ehdr->e_entry - phdr->p_vaddr ) )
                    < phdr->p_filesz ) {
                if ( ! image->priv.phys ) {
                        image->priv.phys = ( dest + e_offset );
                        DBGC ( image, "ELF %p found virtual entry point at %lx"
                               " (virt %lx)\n", image, image->priv.phys,
                               ( ( unsigned long ) ehdr->e_entry ) );
                }
        }

        return 0;
}

/**
 * Load ELF image into memory
 *
 * @v image             ELF file
 * @ret rc              Return status code
 */
int elf_load ( struct image *image ) {
        Elf_Ehdr ehdr;
        Elf_Phdr phdr;
        Elf_Off phoff;
        unsigned int phnum;
        int rc;

        /* Image type must already have been set by caller */
        assert ( image->type != NULL );

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

        /* Invalidate execution address */
        image->priv.phys = 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 ) ) != 0 )
                        return rc;
        }

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

        return 0;
}