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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.
*/
#include <realmode.h>
#include <biosint.h>
#include <basemem.h>
#include <gpxe/init.h>
#include <gpxe/hidemem.h>
/** Alignment for hidden memory regions */
#define ALIGN_HIDDEN 4096 /* 4kB page alignment should be enough */
/**
* A hidden region of Etherboot
*
* This represents a region that will be edited out of the system's
* memory map.
*
* This structure is accessed by assembly code, so must not be
* changed.
*/
struct hidden_region {
/* Physical start address */
physaddr_t start;
/* Physical end address */
physaddr_t end;
};
/**
* List of hidden regions
*
* Must be terminated by a zero entry.
*/
struct hidden_region __data16_array ( hidden_regions, [] ) = {
[TEXT] = { 0, 0 },
[BASEMEM] = { ( 640 * 1024 ), ( 640 * 1024 ) },
[EXTMEM] = { 0, 0 },
{ 0, 0, } /* Terminator */
};
#define hidden_regions __use_data16 ( hidden_regions )
/** Assembly routine in e820mangler.S */
extern void int15();
/** Vector for storing original INT 15 handler */
extern struct segoff __text16 ( int15_vector );
#define int15_vector __use_text16 ( int15_vector )
/**
* Hide region of memory from system memory map
*
* @v start Start of region
* @v end End of region
*/
void hide_region ( unsigned int region_id, physaddr_t start, physaddr_t end ) {
struct hidden_region *region = &hidden_regions[region_id];
/* Some operating systems get a nasty shock if a region of the
* E820 map seems to start on a non-page boundary. Make life
* safer by rounding out our edited region.
*/
region->start = ( start & ~( ALIGN_HIDDEN - 1 ) );
region->end = ( ( end + ALIGN_HIDDEN - 1 ) & ~( ALIGN_HIDDEN - 1 ) );
DBG ( "Hiding region %d [%lx,%lx)\n",
region_id, region->start, region->end );
}
/**
* Hide Etherboot text
*
*/
static void hide_text ( void ) {
/* The linker defines these symbols for us */
extern char _text[];
extern char _end[];
hide_region ( TEXT, virt_to_phys ( _text ), virt_to_phys ( _end ) );
}
/**
* Hide used base memory
*
*/
void hide_basemem ( void ) {
/* Hide from the top of free base memory to 640kB. Don't use
* hide_region(), because we don't want this rounded to the
* nearest page boundary.
*/
hidden_regions[BASEMEM].start = ( get_fbms() * 1024 );
}
/**
* Hide Etherboot
*
* Installs an INT 15 handler to edit Etherboot out of the memory map
* returned by the BIOS.
*/
static void hide_etherboot ( void ) {
/* Initialise the hidden regions */
hide_text();
hide_basemem();
/* Hook INT 15 */
hook_bios_interrupt ( 0x15, ( unsigned int ) int15,
&int15_vector );
}
/**
* Unhide Etherboot
*
* Uninstalls the INT 15 handler installed by hide_etherboot(), if
* possible.
*/
static void unhide_etherboot ( int flags __unused ) {
/* If we have more than one hooked interrupt at this point, it
* means that some other vector is still hooked, in which case
* we can't safely unhook INT 15 because we need to keep our
* memory protected. (We expect there to be at least one
* hooked interrupt, because INT 15 itself is still hooked).
*/
if ( hooked_bios_interrupts > 1 ) {
DBG ( "Cannot unhide: %d interrupt vectors still hooked\n",
hooked_bios_interrupts );
return;
}
/* Try to unhook INT 15. If it fails, then just leave it
* hooked; it takes care of protecting itself. :)
*/
unhook_bios_interrupt ( 0x15, ( unsigned int ) int15,
&int15_vector );
}
/** Hide Etherboot startup function */
struct startup_fn hide_etherboot_startup_fn __startup_fn ( STARTUP_EARLY ) = {
.startup = hide_etherboot,
.shutdown = unhide_etherboot,
};
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