int13.c

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/*
 * Copyright (C) 2006 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 );

#include <stdint.h>
#include <limits.h>
#include <byteswap.h>
#include <errno.h>
#include <assert.h>
#include <gpxe/list.h>
#include <gpxe/blockdev.h>
#include <gpxe/memmap.h>
#include <realmode.h>
#include <bios.h>
#include <biosint.h>
#include <bootsector.h>
#include <int13.h>

/** @file
 *
 * INT 13 emulation
 *
 * This module provides a mechanism for exporting block devices via
 * the BIOS INT 13 disk interrupt interface.  
 *
 */

/** Vector for chaining to other INT 13 handlers */
static struct segoff __text16 ( int13_vector );
#define int13_vector __use_text16 ( int13_vector )

/** Assembly wrapper */
extern void int13_wrapper ( void );

/** List of registered emulated drives */
static LIST_HEAD ( drives );

/**
 * Number of BIOS drives
 *
 * Note that this is the number of drives in the system as a whole
 * (i.e. a mirror of the counter at 40:75), rather than a count of the
 * number of emulated drives.
 */
static uint8_t num_drives;

/**
 * Update BIOS drive count
 */
static void int13_set_num_drives ( void ) {
        struct int13_drive *drive;

        /* Get current drive count */
        get_real ( num_drives, BDA_SEG, BDA_NUM_DRIVES );

        /* Ensure count is large enough to cover all of our emulated drives */
        list_for_each_entry ( drive, &drives, list ) {
                if ( num_drives <= ( drive->drive & 0x7f ) )
                        num_drives = ( ( drive->drive & 0x7f ) + 1 );
        }

        /* Update current drive count */
        put_real ( num_drives, BDA_SEG, BDA_NUM_DRIVES );
}

/**
 * Check number of drives
 */
static void int13_check_num_drives ( void ) {
        uint8_t check_num_drives;

        get_real ( check_num_drives, BDA_SEG, BDA_NUM_DRIVES );
        if ( check_num_drives != num_drives ) {
                int13_set_num_drives();
                DBG ( "INT13 fixing up number of drives from %d to %d\n",
                      check_num_drives, num_drives );
        }
}

/**
 * INT 13, 00 - Reset disk system
 *
 * @v drive             Emulated drive
 * @ret status          Status code
 */
static int int13_reset ( struct int13_drive *drive __unused,
                         struct i386_all_regs *ix86 __unused ) {
        DBG ( "Reset drive\n" );
        return 0;
}

/**
 * INT 13, 01 - Get status of last operation
 *
 * @v drive             Emulated drive
 * @ret status          Status code
 */
static int int13_get_last_status ( struct int13_drive *drive,
                                   struct i386_all_regs *ix86 __unused ) {
        DBG ( "Get status of last operation\n" );
        return drive->last_status;
}

/**
 * Read / write sectors
 *
 * @v drive             Emulated drive
 * @v al                Number of sectors to read or write (must be nonzero)
 * @v ch                Low bits of cylinder number
 * @v cl (bits 7:6)     High bits of cylinder number
 * @v cl (bits 5:0)     Sector number
 * @v dh                Head number
 * @v es:bx             Data buffer
 * @v io                Read / write method
 * @ret status          Status code
 * @ret al              Number of sectors read or written
 */
static int int13_rw_sectors ( struct int13_drive *drive,
                              struct i386_all_regs *ix86,
                              int ( * io ) ( struct block_device *blockdev,
                                             uint64_t block,
                                             unsigned long count,
                                             userptr_t buffer ) ) {
        struct block_device *blockdev = drive->blockdev;
        unsigned int cylinder, head, sector;
        unsigned long lba;
        unsigned int count;
        userptr_t buffer;
        int rc;

        /* Validate blocksize */
        if ( blockdev->blksize != INT13_BLKSIZE ) {
                DBG ( "Invalid blocksize (%zd) for non-extended read/write\n",
                      blockdev->blksize );
                return -INT13_STATUS_INVALID;
        }
        
        /* Calculate parameters */
        cylinder = ( ( ( ix86->regs.cl & 0xc0 ) << 2 ) | ix86->regs.ch );
        assert ( cylinder < drive->cylinders );
        head = ix86->regs.dh;
        assert ( head < drive->heads );
        sector = ( ix86->regs.cl & 0x3f );
        assert ( ( sector >= 1 ) && ( sector <= drive->sectors_per_track ) );
        lba = ( ( ( ( cylinder * drive->heads ) + head )
                  * drive->sectors_per_track ) + sector - 1 );
        count = ix86->regs.al;
        buffer = real_to_user ( ix86->segs.es, ix86->regs.bx );

        DBG ( "C/H/S %d/%d/%d = LBA %#lx <-> %04x:%04x (count %d)\n", cylinder,
              head, sector, lba, ix86->segs.es, ix86->regs.bx, count );

        /* Read from / write to block device */
        if ( ( rc = io ( blockdev, lba, count, buffer ) ) != 0 ) {
                DBG ( "INT 13 failed: %s\n", strerror ( rc ) );
                return -INT13_STATUS_READ_ERROR;
        }

        return 0;
}

/**
 * INT 13, 02 - Read sectors
 *
 * @v drive             Emulated drive
 * @v al                Number of sectors to read (must be nonzero)
 * @v ch                Low bits of cylinder number
 * @v cl (bits 7:6)     High bits of cylinder number
 * @v cl (bits 5:0)     Sector number
 * @v dh                Head number
 * @v es:bx             Data buffer
 * @ret status          Status code
 * @ret al              Number of sectors read
 */
static int int13_read_sectors ( struct int13_drive *drive,
                                struct i386_all_regs *ix86 ) {
        DBG ( "Read: " );
        return int13_rw_sectors ( drive, ix86, drive->blockdev->op->read );
}

/**
 * INT 13, 03 - Write sectors
 *
 * @v drive             Emulated drive
 * @v al                Number of sectors to write (must be nonzero)
 * @v ch                Low bits of cylinder number
 * @v cl (bits 7:6)     High bits of cylinder number
 * @v cl (bits 5:0)     Sector number
 * @v dh                Head number
 * @v es:bx             Data buffer
 * @ret status          Status code
 * @ret al              Number of sectors written
 */
static int int13_write_sectors ( struct int13_drive *drive,
                                 struct i386_all_regs *ix86 ) {
        DBG ( "Write: " );
        return int13_rw_sectors ( drive, ix86, drive->blockdev->op->write );
}

/**
 * INT 13, 08 - Get drive parameters
 *
 * @v drive             Emulated drive
 * @ret status          Status code
 * @ret ch              Low bits of maximum cylinder number
 * @ret cl (bits 7:6)   High bits of maximum cylinder number
 * @ret cl (bits 5:0)   Maximum sector number
 * @ret dh              Maximum head number
 * @ret dl              Number of drives
 */
static int int13_get_parameters ( struct int13_drive *drive,
                                  struct i386_all_regs *ix86 ) {
        unsigned int max_cylinder = drive->cylinders - 1;
        unsigned int max_head = drive->heads - 1;
        unsigned int max_sector = drive->sectors_per_track; /* sic */

        DBG ( "Get drive parameters\n" );

        ix86->regs.ch = ( max_cylinder & 0xff );
        ix86->regs.cl = ( ( ( max_cylinder >> 8 ) << 6 ) | max_sector );
        ix86->regs.dh = max_head;
        get_real ( ix86->regs.dl, BDA_SEG, BDA_NUM_DRIVES );
        return 0;
}

/**
 * INT 13, 15 - Get disk type
 *
 * @v drive             Emulated drive
 * @ret ah              Type code
 * @ret cx:dx           Sector count
 * @ret status          Status code / disk type
 */
static int int13_get_disk_type ( struct int13_drive *drive,
                                 struct i386_all_regs *ix86 ) {
        uint32_t blocks;

        DBG ( "Get disk type\n" );
        blocks = ( ( drive->blockdev->blocks <= 0xffffffffUL ) ?
                   drive->blockdev->blocks : 0xffffffffUL );
        ix86->regs.cx = ( blocks >> 16 );
        ix86->regs.dx = ( blocks & 0xffff );
        return INT13_DISK_TYPE_HDD;
}

/**
 * INT 13, 41 - Extensions installation check
 *
 * @v drive             Emulated drive
 * @v bx                0x55aa
 * @ret bx              0xaa55
 * @ret cx              Extensions API support bitmap
 * @ret status          Status code / API version
 */
static int int13_extension_check ( struct int13_drive *drive __unused,
                                   struct i386_all_regs *ix86 ) {
        if ( ix86->regs.bx == 0x55aa ) {
                DBG ( "INT 13 extensions installation check\n" );
                ix86->regs.bx = 0xaa55;
                ix86->regs.cx = INT13_EXTENSION_LINEAR;
                return INT13_EXTENSION_VER_1_X;
        } else {
                return -INT13_STATUS_INVALID;
        }
}

/**
 * Extended read / write
 *
 * @v drive             Emulated drive
 * @v ds:si             Disk address packet
 * @v io                Read / write method
 * @ret status          Status code
 */
static int int13_extended_rw ( struct int13_drive *drive,
                               struct i386_all_regs *ix86,
                               int ( * io ) ( struct block_device *blockdev,
                                              uint64_t block,
                                              unsigned long count,
                                              userptr_t buffer ) ) {
        struct block_device *blockdev = drive->blockdev;
        struct int13_disk_address addr;
        uint64_t lba;
        unsigned long count;
        userptr_t buffer;
        int rc;

        /* Read parameters from disk address structure */
        copy_from_real ( &addr, ix86->segs.ds, ix86->regs.si, sizeof ( addr ));
        lba = addr.lba;
        count = addr.count;
        buffer = real_to_user ( addr.buffer.segment, addr.buffer.offset );

        DBG ( "LBA %#llx <-> %04x:%04x (count %ld)\n", (unsigned long long)lba,
              addr.buffer.segment, addr.buffer.offset, count );
        
        /* Read from / write to block device */
        if ( ( rc = io ( blockdev, lba, count, buffer ) ) != 0 ) {
                DBG ( "INT 13 failed: %s\n", strerror ( rc ) );
                return -INT13_STATUS_READ_ERROR;
        }

        return 0;
}

/**
 * INT 13, 42 - Extended read
 *
 * @v drive             Emulated drive
 * @v ds:si             Disk address packet
 * @ret status          Status code
 */
static int int13_extended_read ( struct int13_drive *drive,
                                 struct i386_all_regs *ix86 ) {
        DBG ( "Extended read: " );
        return int13_extended_rw ( drive, ix86, drive->blockdev->op->read );
}

/**
 * INT 13, 43 - Extended write
 *
 * @v drive             Emulated drive
 * @v ds:si             Disk address packet
 * @ret status          Status code
 */
static int int13_extended_write ( struct int13_drive *drive,
                                  struct i386_all_regs *ix86 ) {
        DBG ( "Extended write: " );
        return int13_extended_rw ( drive, ix86, drive->blockdev->op->write );
}

/**
 * INT 13, 48 - Get extended parameters
 *
 * @v drive             Emulated drive
 * @v ds:si             Drive parameter table
 * @ret status          Status code
 */
static int int13_get_extended_parameters ( struct int13_drive *drive,
                                           struct i386_all_regs *ix86 ) {
        struct int13_disk_parameters params = {
                .bufsize = sizeof ( params ),
                .flags = INT13_FL_DMA_TRANSPARENT,
                .cylinders = drive->cylinders,
                .heads = drive->heads,
                .sectors_per_track = drive->sectors_per_track,
                .sectors = drive->blockdev->blocks,
                .sector_size = drive->blockdev->blksize,
        };
        
        DBG ( "Get extended drive parameters to %04x:%04x\n",
              ix86->segs.ds, ix86->regs.si );

        copy_to_real ( ix86->segs.ds, ix86->regs.si, &params,
                       sizeof ( params ) );
        return 0;
}

/**
 * INT 13 handler
 *
 */
static __asmcall void int13 ( struct i386_all_regs *ix86 ) {
        int command = ix86->regs.ah;
        unsigned int bios_drive = ix86->regs.dl;
        struct int13_drive *drive;
        int status;

        /* Check BIOS hasn't killed off our drive */
        int13_check_num_drives();

        list_for_each_entry ( drive, &drives, list ) {

                if ( bios_drive != drive->drive ) {
                        /* Remap any accesses to this drive's natural number */
                        if ( bios_drive == drive->natural_drive ) {
                                DBG ( "INT 13,%04x (%02x) remapped to "
                                      "(%02x)\n", ix86->regs.ax,
                                      bios_drive, drive->drive );
                                ix86->regs.dl = drive->drive;
                                return;
                        }
                        continue;
                }
                
                DBG ( "INT 13,%04x (%02x): ", ix86->regs.ax, drive->drive );

                switch ( command ) {
                case INT13_RESET:
                        status = int13_reset ( drive, ix86 );
                        break;
                case INT13_GET_LAST_STATUS:
                        status = int13_get_last_status ( drive, ix86 );
                        break;
                case INT13_READ_SECTORS:
                        status = int13_read_sectors ( drive, ix86 );
                        break;
                case INT13_WRITE_SECTORS:
                        status = int13_write_sectors ( drive, ix86 );
                        break;
                case INT13_GET_PARAMETERS:
                        status = int13_get_parameters ( drive, ix86 );
                        break;
                case INT13_GET_DISK_TYPE:
                        status = int13_get_disk_type ( drive, ix86 );
                        break;
                case INT13_EXTENSION_CHECK:
                        status = int13_extension_check ( drive, ix86 );
                        break;
                case INT13_EXTENDED_READ:
                        status = int13_extended_read ( drive, ix86 );
                        break;
                case INT13_EXTENDED_WRITE:
                        status = int13_extended_write ( drive, ix86 );
                        break;
                case INT13_GET_EXTENDED_PARAMETERS:
                        status = int13_get_extended_parameters ( drive, ix86 );
                        break;
                default:
                        DBG ( "*** Unrecognised INT 13 ***\n" );
                        status = -INT13_STATUS_INVALID;
                        break;
                }

                /* Store status for INT 13,01 */
                drive->last_status = status;

                /* Negative status indicates an error */
                if ( status < 0 ) {
                        status = -status;
                        DBG ( "INT 13 returning failure status %x\n", status );
                } else {
                        ix86->flags &= ~CF;
                }
                ix86->regs.ah = status;

                /* Set OF to indicate to wrapper not to chain this call */
                ix86->flags |= OF;

                return;
        }
}

/**
 * Hook INT 13 handler
 *
 */
static void hook_int13 ( void ) {
        /* Assembly wrapper to call int13().  int13() sets OF if we
         * should not chain to the previous handler.  (The wrapper
         * clears CF and OF before calling int13()).
         */
        __asm__  __volatile__ (
               TEXT16_CODE ( "\nint13_wrapper:\n\t"
                             /* Preserve %ax and %dx for future reference */
                             "pushw %%bp\n\t"
                             "movw %%sp, %%bp\n\t"                           
                             "pushw %%ax\n\t"
                             "pushw %%dx\n\t"
                             /* Clear OF, set CF, call int13() */
                             "orb $0, %%al\n\t" 
                             "stc\n\t"
                             "pushl %0\n\t"
                             "pushw %%cs\n\t"
                             "call prot_call\n\t"
                             /* Chain if OF not set */
                             "jo 1f\n\t"
                             "pushfw\n\t"
                             "lcall *%%cs:int13_vector\n\t"
                             "\n1:\n\t"
                             /* Overwrite flags for iret */
                             "pushfw\n\t"
                             "popw 6(%%bp)\n\t"
                             /* Fix up %dl:
                              *
                              * INT 13,15 : do nothing
                              * INT 13,08 : load with number of drives
                              * all others: restore original value
                              */
                             "cmpb $0x15, -1(%%bp)\n\t"
                             "je 2f\n\t"
                             "movb -4(%%bp), %%dl\n\t"
                             "cmpb $0x08, -1(%%bp)\n\t"
                             "jne 2f\n\t"
                             "pushw %%ds\n\t"
                             "pushw %1\n\t"
                             "popw %%ds\n\t"
                             "movb %c2, %%dl\n\t"
                             "popw %%ds\n\t"
                             /* Return */
                             "\n2:\n\t"
                             "movw %%bp, %%sp\n\t"
                             "popw %%bp\n\t"
                             "iret\n\t" )
               : : "i" ( int13 ), "i" ( BDA_SEG ), "i" ( BDA_NUM_DRIVES ) );

        hook_bios_interrupt ( 0x13, ( unsigned int ) int13_wrapper,
                              &int13_vector );
}

/**
 * Unhook INT 13 handler
 */
static void unhook_int13 ( void ) {
        unhook_bios_interrupt ( 0x13, ( unsigned int ) int13_wrapper,
                                &int13_vector );
}

/**
 * Guess INT 13 drive geometry
 *
 * @v drive             Emulated drive
 *
 * Guesses the drive geometry by inspecting the partition table.
 */
static void guess_int13_geometry ( struct int13_drive *drive ) {
        struct master_boot_record mbr;
        struct partition_table_entry *partition;
        unsigned int guessed_heads = 255;
        unsigned int guessed_sectors_per_track = 63;
        unsigned long blocks;
        unsigned long blocks_per_cyl;
        unsigned int i;

        /* Don't even try when the blksize is invalid for C/H/S access */
        if ( drive->blockdev->blksize != INT13_BLKSIZE )
                return;

        /* Scan through partition table and modify guesses for heads
         * and sectors_per_track if we find any used partitions.
         */
        if ( drive->blockdev->op->read ( drive->blockdev, 0, 1,
                                         virt_to_user ( &mbr ) ) == 0 ) {
                for ( i = 0 ; i < 4 ; i++ ) {
                        partition = &mbr.partitions[i];
                        if ( ! partition->type )
                                continue;
                        guessed_heads =
                                ( PART_HEAD ( partition->chs_end ) + 1 );
                        guessed_sectors_per_track = 
                                PART_SECTOR ( partition->chs_end );
                        DBG ( "Guessing C/H/S xx/%d/%d based on partition "
                              "%d\n", guessed_heads,
                              guessed_sectors_per_track, ( i + 1 ) );
                }
        } else {
                DBG ( "Could not read partition table to guess geometry\n" );
        }

        /* Apply guesses if no geometry already specified */
        if ( ! drive->heads )
                drive->heads = guessed_heads;
        if ( ! drive->sectors_per_track )
                drive->sectors_per_track = guessed_sectors_per_track;
        if ( ! drive->cylinders ) {
                /* Avoid attempting a 64-bit divide on a 32-bit system */
                blocks = ( ( drive->blockdev->blocks <= ULONG_MAX ) ?
                           drive->blockdev->blocks : ULONG_MAX );
                blocks_per_cyl = ( drive->heads * drive->sectors_per_track );
                assert ( blocks_per_cyl != 0 );
                drive->cylinders = ( blocks / blocks_per_cyl );
                if ( drive->cylinders > 1024 )
                        drive->cylinders = 1024;
        }
}

/**
 * Register INT 13 emulated drive
 *
 * @v drive             Emulated drive
 *
 * Registers the drive with the INT 13 emulation subsystem, and hooks
 * the INT 13 interrupt vector (if not already hooked).
 *
 * The underlying block device must be valid.  A drive number and
 * geometry will be assigned if left blank.
 */
void register_int13_drive ( struct int13_drive *drive ) {
        uint8_t num_drives;

        /* Give drive a default geometry if none specified */
        guess_int13_geometry ( drive );

        /* Assign natural drive number */
        get_real ( num_drives, BDA_SEG, BDA_NUM_DRIVES );
        drive->natural_drive = ( num_drives | 0x80 );

        /* Assign drive number */
        if ( ( drive->drive & 0xff ) == 0xff ) {
                /* Drive number == -1 => use natural drive number */
                drive->drive = drive->natural_drive;
        } else {
                /* Use specified drive number (+0x80 if necessary) */
                drive->drive |= 0x80;
        }

        DBG ( "Registered INT13 drive %02x (naturally %02x) with C/H/S "
              "geometry %d/%d/%d\n", drive->drive, drive->natural_drive,
              drive->cylinders, drive->heads, drive->sectors_per_track );

        /* Hook INT 13 vector if not already hooked */
        if ( list_empty ( &drives ) )
                hook_int13();

        /* Add to list of emulated drives */
        list_add ( &drive->list, &drives );

        /* Update BIOS drive count */
        int13_set_num_drives();
}

/**
 * Unregister INT 13 emulated drive
 *
 * @v drive             Emulated drive
 *
 * Unregisters the drive from the INT 13 emulation subsystem.  If this
 * is the last emulated drive, the INT 13 vector is unhooked (if
 * possible).
 */
void unregister_int13_drive ( struct int13_drive *drive ) {
        /* Remove from list of emulated drives */
        list_del ( &drive->list );

        /* Should adjust BIOS drive count, but it's difficult to do so
         * reliably.
         */

        DBG ( "Unregistered INT13 drive %02x\n", drive->drive );

        /* Unhook INT 13 vector if no more drives */
        if ( list_empty ( &drives ) )
                unhook_int13();
}

/**
 * Attempt to boot from an INT 13 drive
 *
 * @v drive             Drive number
 * @ret rc              Return status code
 *
 * This boots from the specified INT 13 drive by loading the Master
 * Boot Record to 0000:7c00 and jumping to it.  INT 18 is hooked to
 * capture an attempt by the MBR to boot the next device.  (This is
 * the closest thing to a return path from an MBR).
 *
 * Note that this function can never return success, by definition.
 */
int int13_boot ( unsigned int drive ) {
        struct memory_map memmap;
        int status, signature;
        int discard_c, discard_d;
        int rc;

        DBG ( "Booting from INT 13 drive %02x\n", drive );

        /* Use INT 13 to read the boot sector */
        __asm__ __volatile__ ( REAL_CODE ( "pushw %%es\n\t"
                                           "pushw $0\n\t"
                                           "popw %%es\n\t"
                                           "stc\n\t"
                                           "sti\n\t"
                                           "int $0x13\n\t"
                                           "sti\n\t" /* BIOS bugs */
                                           "jc 1f\n\t"
                                           "xorl %%eax, %%eax\n\t"
                                           "\n1:\n\t"
                                           "movzwl %%es:0x7dfe, %%ebx\n\t"
                                           "popw %%es\n\t" )
                               : "=a" ( status ), "=b" ( signature ),
                                 "=c" ( discard_c ), "=d" ( discard_d )
                               : "a" ( 0x0201 ), "b" ( 0x7c00 ),
                                 "c" ( 1 ), "d" ( drive ) );
        if ( status )
                return -EIO;

        /* Check signature is correct */
        if ( signature != be16_to_cpu ( 0x55aa ) ) {
                DBG ( "Invalid disk signature %#04x (should be 0x55aa)\n",
                      cpu_to_be16 ( signature ) );
                return -ENOEXEC;
        }

        /* Dump out memory map prior to boot, if memmap debugging is
         * enabled.  Not required for program flow, but we have so
         * many problems that turn out to be memory-map related that
         * it's worth doing.
         */
        get_memmap ( &memmap );

        /* Jump to boot sector */
        if ( ( rc = call_bootsector ( 0x0, 0x7c00, drive ) ) != 0 ) {
                DBG ( "INT 13 drive %02x boot returned: %s\n",
                      drive, strerror ( rc ) );
                return rc;
        }

        return -ECANCELED; /* -EIMPOSSIBLE */
}