nbi.c

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#include <errno.h>
#include <assert.h>
#include <realmode.h>
#include <memsizes.h>
#include <basemem_packet.h>
#include <ipxe/uaccess.h>
#include <ipxe/segment.h>
#include <ipxe/init.h>
#include <ipxe/netdevice.h>
#include <ipxe/fakedhcp.h>
#include <ipxe/image.h>
#include <ipxe/features.h>
#include <ipxe/version.h>

/** @file
 *
 * NBI image format.
 *
 * The Net Boot Image format is defined by the "Draft Net Boot Image
 * Proposal 0.3" by Jamie Honan, Gero Kuhlmann and Ken Yap.  It is now
 * considered to be a legacy format, but it still included because a
 * large amount of software (e.g. nymph, LTSP) makes use of NBI files.
 *
 * Etherboot does not implement the INT 78 callback interface
 * described by the NBI specification.  For a callback interface on
 * x86 architecture, use PXE.
 *
 */

FEATURE ( FEATURE_IMAGE, "NBI", DHCP_EB_FEATURE_NBI, 1 );

/**
 * An NBI image header
 *
 * Note that the length field uses a peculiar encoding; use the
 * NBI_LENGTH() macro to decode the actual header length.
 *
 */
struct imgheader {
        unsigned long magic;            /**< Magic number (NBI_MAGIC) */
        union {
                unsigned char length;   /**< Nibble-coded header length */
                unsigned long flags;    /**< Image flags */
        };
        segoff_t location;              /**< 16-bit seg:off header location */
        union {
                segoff_t segoff;        /**< 16-bit seg:off entry point */
                unsigned long linear;   /**< 32-bit entry point */
        } execaddr;
} __attribute__ (( packed ));

/** NBI magic number */
#define NBI_MAGIC 0x1B031336UL

/* Interpretation of the "length" fields */
#define NBI_NONVENDOR_LENGTH(len)       ( ( (len) & 0x0f ) << 2 )
#define NBI_VENDOR_LENGTH(len)          ( ( (len) & 0xf0 ) >> 2 )
#define NBI_LENGTH(len) ( NBI_NONVENDOR_LENGTH(len) + NBI_VENDOR_LENGTH(len) )

/* Interpretation of the "flags" fields */
#define NBI_PROGRAM_RETURNS(flags)      ( (flags) & ( 1 << 8 ) )
#define NBI_LINEAR_EXEC_ADDR(flags)     ( (flags) & ( 1 << 31 ) )

/** NBI header length */
#define NBI_HEADER_LENGTH       512

/**
 * An NBI segment header
 *
 * Note that the length field uses a peculiar encoding; use the
 * NBI_LENGTH() macro to decode the actual header length.
 *
 */
struct segheader {
        unsigned char length;           /**< Nibble-coded header length */
        unsigned char vendortag;        /**< Vendor-defined private tag */
        unsigned char reserved;
        unsigned char flags;            /**< Segment flags */
        unsigned long loadaddr;         /**< Load address */
        unsigned long imglength;        /**< Segment length in NBI file */
        unsigned long memlength;        /**< Segment length in memory */
};

/* Interpretation of the "flags" fields */
#define NBI_LOADADDR_FLAGS(flags)       ( (flags) & 0x03 )
#define NBI_LOADADDR_ABS                0x00
#define NBI_LOADADDR_AFTER              0x01
#define NBI_LOADADDR_END                0x02
#define NBI_LOADADDR_BEFORE             0x03
#define NBI_LAST_SEGHEADER(flags)       ( (flags) & ( 1 << 2 ) )

/* Define a type for passing info to a loaded program */
struct ebinfo {
        uint8_t  major, minor;  /* Version */
        uint16_t flags;         /* Bit flags */
};

/**
 * Prepare a segment for an NBI image
 *
 * @v image             NBI image
 * @v offset            Offset within NBI image
 * @v filesz            Length of initialised-data portion of the segment
 * @v memsz             Total length of the segment
 * @v src               Source for initialised data
 * @ret rc              Return status code
 */
static int nbi_prepare_segment ( struct image *image, size_t offset __unused,
                                 userptr_t dest, size_t filesz, size_t memsz ){
        int rc;

        if ( ( rc = prep_segment ( dest, filesz, memsz ) ) != 0 ) {
                DBGC ( image, "NBI %p could not prepare segment: %s\n",
                       image, strerror ( rc ) );
                return rc;
        }

        return 0;
}

/**
 * Load a segment for an NBI image
 *
 * @v image             NBI image
 * @v offset            Offset within NBI image
 * @v filesz            Length of initialised-data portion of the segment
 * @v memsz             Total length of the segment
 * @v src               Source for initialised data
 * @ret rc              Return status code
 */
static int nbi_load_segment ( struct image *image, size_t offset,
                              userptr_t dest, size_t filesz,
                              size_t memsz __unused ) {
        memcpy_user ( dest, 0, image->data, offset, filesz );
        return 0;
}

/**
 * Process segments of an NBI image
 *
 * @v image             NBI image
 * @v imgheader         Image header information
 * @v process           Function to call for each segment
 * @ret rc              Return status code
 */
static int nbi_process_segments ( struct image *image,
                                  struct imgheader *imgheader,
                                  int ( * process ) ( struct image *image,
                                                      size_t offset,
                                                      userptr_t dest,
                                                      size_t filesz,
                                                      size_t memsz ) ) {
        struct segheader sh;
        size_t offset = 0;
        size_t sh_off;
        userptr_t dest;
        size_t filesz;
        size_t memsz;
        int rc;
        
        /* Copy image header to target location */
        dest = real_to_user ( imgheader->location.segment,
                              imgheader->location.offset );
        filesz = memsz = NBI_HEADER_LENGTH;
        if ( ( rc = process ( image, offset, dest, filesz, memsz ) ) != 0 )
                return rc;
        offset += filesz;

        /* Process segments in turn */
        sh_off = NBI_LENGTH ( imgheader->length );
        do {
                /* Read segment header */
                copy_from_user ( &sh, image->data, sh_off, sizeof ( sh ) );
                if ( sh.length == 0 ) {
                        /* Avoid infinite loop? */
                        DBGC ( image, "NBI %p invalid segheader length 0\n",
                               image );
                        return -ENOEXEC;
                }
                
                /* Calculate segment load address */
                switch ( NBI_LOADADDR_FLAGS ( sh.flags ) ) {
                case NBI_LOADADDR_ABS:
                        dest = phys_to_user ( sh.loadaddr );
                        break;
                case NBI_LOADADDR_AFTER:
                        dest = userptr_add ( dest, memsz + sh.loadaddr );
                        break;
                case NBI_LOADADDR_BEFORE:
                        dest = userptr_add ( dest, -sh.loadaddr );
                        break;
                case NBI_LOADADDR_END:
                        /* Not correct according to the spec, but
                         * maintains backwards compatibility with
                         * previous versions of Etherboot.
                         */
                        dest = phys_to_user ( ( extmemsize() + 1024 ) * 1024
                                              - sh.loadaddr );
                        break;
                default:
                        /* Cannot be reached */
                        assert ( 0 );
                }

                /* Process this segment */
                filesz = sh.imglength;
                memsz = sh.memlength;
                if ( ( offset + filesz ) > image->len ) {
                        DBGC ( image, "NBI %p segment outside file\n", image );
                        return -ENOEXEC;
                }
                if ( ( rc = process ( image, offset, dest,
                                      filesz, memsz ) ) != 0 ) {
                        return rc;
                }
                offset += filesz;

                /* Next segheader */
                sh_off += NBI_LENGTH ( sh.length );
                if ( sh_off >= NBI_HEADER_LENGTH ) {
                        DBGC ( image, "NBI %p header overflow\n", image );
                        return -ENOEXEC;
                }

        } while ( ! NBI_LAST_SEGHEADER ( sh.flags ) );

        if ( offset != image->len ) {
                DBGC ( image, "NBI %p length wrong (file %zd, metadata %zd)\n",
                       image, image->len, offset );
                return -ENOEXEC;
        }

        return 0;
}

/**
 * Boot a 16-bit NBI image
 *
 * @v imgheader         Image header information
 * @ret rc              Return status code, if image returns
 */
static int nbi_boot16 ( struct image *image, struct imgheader *imgheader ) {
        int discard_D, discard_S, discard_b;
        int32_t rc;

        DBGC ( image, "NBI %p executing 16-bit image at %04x:%04x\n", image,
               imgheader->execaddr.segoff.segment,
               imgheader->execaddr.segoff.offset );

        __asm__ __volatile__ (
                REAL_CODE ( "pushl %%ebp\n\t"   /* gcc bug */
                            "pushw %%ds\n\t"    /* far pointer to bootp data */
                            "pushw %%bx\n\t"
                            "pushl %%esi\n\t"   /* location */
                            "pushw %%cs\n\t"    /* lcall execaddr */
                            "call 1f\n\t"
                            "jmp 2f\n\t"
                            "\n1:\n\t"
                            "pushl %%edi\n\t"
                            "lret\n\t"
                            "\n2:\n\t"
                            "addw $8,%%sp\n\t"  /* clean up stack */
                            "popl %%ebp\n\t"    /* gcc bug */ )
                : "=a" ( rc ), "=D" ( discard_D ), "=S" ( discard_S ),
                  "=b" ( discard_b )
                : "D" ( imgheader->execaddr.segoff ),
                  "S" ( imgheader->location ),
                  "b" ( __from_data16 ( basemem_packet ) )
                : "ecx", "edx" );

        return rc;
}

/**
 * Boot a 32-bit NBI image
 *
 * @v imgheader         Image header information
 * @ret rc              Return status code, if image returns
 */
static int nbi_boot32 ( struct image *image, struct imgheader *imgheader ) {
        struct ebinfo loaderinfo = {
                product_major_version, product_minor_version,
                0
        };
        int discard_D, discard_S, discard_b;
        int32_t rc;

        DBGC ( image, "NBI %p executing 32-bit image at %lx\n",
               image, imgheader->execaddr.linear );

        /* Jump to OS with flat physical addressing */
        __asm__ __volatile__ (
                PHYS_CODE ( "pushl %%ebp\n\t" /* gcc bug */
                            "pushl %%ebx\n\t" /* bootp data */
                            "pushl %%esi\n\t" /* imgheader */
                            "pushl %%eax\n\t" /* loaderinfo */
                            "call *%%edi\n\t"
                            "addl $12, %%esp\n\t" /* clean up stack */
                            "popl %%ebp\n\t" /* gcc bug */ )
                : "=a" ( rc ), "=D" ( discard_D ), "=S" ( discard_S ),
                  "=b" ( discard_b )
                : "D" ( imgheader->execaddr.linear ),
                  "S" ( ( imgheader->location.segment << 4 ) +
                        imgheader->location.offset ),
                  "b" ( virt_to_phys ( basemem_packet ) ),
                  "a" ( virt_to_phys ( &loaderinfo ) )
                : "ecx", "edx", "memory" );

        return rc;
}

/**
 * Prepare DHCP parameter block for NBI image
 *
 * @v image             NBI image
 * @ret rc              Return status code
 */
static int nbi_prepare_dhcp ( struct image *image ) {
        struct net_device *boot_netdev;
        int rc;

        boot_netdev = last_opened_netdev();
        if ( ! boot_netdev ) {
                DBGC ( image, "NBI %p could not identify a network device\n",
                       image );
                return -ENODEV;
        }

        if ( ( rc = create_fakedhcpack ( boot_netdev, basemem_packet,
                                         sizeof ( basemem_packet ) ) ) != 0 ) {
                DBGC ( image, "NBI %p failed to build DHCP packet\n", image );
                return rc;
        }

        return 0;
}

/**
 * Execute a loaded NBI image
 *
 * @v image             NBI image
 * @ret rc              Return status code
 */
static int nbi_exec ( struct image *image ) {
        struct imgheader imgheader;
        int may_return;
        int rc;

        /* Retrieve image header */
        copy_from_user ( &imgheader, image->data, 0, sizeof ( imgheader ) );

        DBGC ( image, "NBI %p placing header at %hx:%hx\n", image,
               imgheader.location.segment, imgheader.location.offset );

        /* NBI files can have overlaps between segments; the bss of
         * one segment may overlap the initialised data of another.  I
         * assume this is a design flaw, but there are images out
         * there that we need to work with.  We therefore do two
         * passes: first to initialise the segments, then to copy the
         * data.  This avoids zeroing out already-copied data.
         */
        if ( ( rc = nbi_process_segments ( image, &imgheader,
                                           nbi_prepare_segment ) ) != 0 )
                return rc;
        if ( ( rc = nbi_process_segments ( image, &imgheader,
                                           nbi_load_segment ) ) != 0 )
                return rc;

        /* Prepare DHCP option block */
        if ( ( rc = nbi_prepare_dhcp ( image ) ) != 0 )
                return rc;

        /* Shut down now if NBI image will not return */
        may_return = NBI_PROGRAM_RETURNS ( imgheader.flags );
        if ( ! may_return )
                shutdown_boot();

        /* Execute NBI image */
        if ( NBI_LINEAR_EXEC_ADDR ( imgheader.flags ) ) {
                rc = nbi_boot32 ( image, &imgheader );
        } else {
                rc = nbi_boot16 ( image, &imgheader );
        }

        if ( ! may_return ) {
                /* Cannot continue after shutdown() called */
                DBGC ( image, "NBI %p returned %d from non-returnable image\n",
                       image, rc  );
                while ( 1 ) {}
        }

        DBGC ( image, "NBI %p returned %d\n", image, rc );

        return rc;
}

/**
 * Probe NBI image
 *
 * @v image             NBI image
 * @ret rc              Return status code
 */
static int nbi_probe ( struct image *image ) {
        struct imgheader imgheader;

        /* If we don't have enough data give up */
        if ( image->len < NBI_HEADER_LENGTH ) {
                DBGC ( image, "NBI %p too short for an NBI image\n", image );
                return -ENOEXEC;
        }

        /* Check image header */
        copy_from_user ( &imgheader, image->data, 0, sizeof ( imgheader ) );
        if ( imgheader.magic != NBI_MAGIC ) {
                DBGC ( image, "NBI %p has no NBI signature\n", image );
                return -ENOEXEC;
        }

        return 0;
}

/** NBI image type */
struct image_type nbi_image_type __image_type ( PROBE_NORMAL ) = {
        .name = "NBI",
        .probe = nbi_probe,
        .exec = nbi_exec,
};