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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., 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 );
#include <assert.h>
#include <realmode.h>
#include <biosint.h>
#include <basemem.h>
#include <fakee820.h>
#include <ipxe/init.h>
#include <ipxe/io.h>
#include <ipxe/hidemem.h>
/** Set to true if you want to test a fake E820 map */
#define FAKE_E820 0
/** Alignment for hidden memory regions */
#define ALIGN_HIDDEN 4096 /* 4kB page alignment should be enough */
/**
* A hidden region of iPXE
*
* 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 */
uint64_t start;
/** Physical end address */
uint64_t end;
};
/** Hidden base memory */
extern struct hidden_region __data16 ( hidemem_base );
#define hidemem_base __use_data16 ( hidemem_base )
/** Hidden umalloc memory */
extern struct hidden_region __data16 ( hidemem_umalloc );
#define hidemem_umalloc __use_data16 ( hidemem_umalloc )
/** Hidden text memory */
extern struct hidden_region __data16 ( hidemem_textdata );
#define hidemem_textdata __use_data16 ( hidemem_textdata )
/** 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 )
/* The linker defines these symbols for us */
extern char _textdata[];
extern char _etextdata[];
extern char _text16_memsz[];
#define _text16_memsz ( ( size_t ) _text16_memsz )
extern char _data16_memsz[];
#define _data16_memsz ( ( size_t ) _data16_memsz )
/**
* Hide region of memory from system memory map
*
* @v region Hidden memory region
* @v start Start of region
* @v end End of region
*/
static void hide_region ( struct hidden_region *region,
physaddr_t start, physaddr_t end ) {
/* 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 [%llx,%llx)\n", region->start, region->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.
*/
hidemem_base.start = ( get_fbms() * 1024 );
}
/**
* Hide umalloc() region
*
*/
void hide_umalloc ( physaddr_t start, physaddr_t end ) {
assert ( end <= virt_to_phys ( _textdata ) );
hide_region ( &hidemem_umalloc, start, end );
}
/**
* Hide .text and .data
*
*/
void hide_textdata ( void ) {
hide_region ( &hidemem_textdata, virt_to_phys ( _textdata ),
virt_to_phys ( _etextdata ) );
}
/**
* Hide Etherboot
*
* Installs an INT 15 handler to edit Etherboot out of the memory map
* returned by the BIOS.
*/
static void hide_etherboot ( void ) {
struct memory_map memmap;
unsigned int rm_ds_top;
unsigned int rm_cs_top;
unsigned int fbms;
/* Dump memory map before mangling */
DBG ( "Hiding iPXE from system memory map\n" );
get_memmap ( &memmap );
/* Hook in fake E820 map, if we're testing one */
if ( FAKE_E820 ) {
DBG ( "Hooking in fake E820 map\n" );
fake_e820();
get_memmap ( &memmap );
}
/* Initialise the hidden regions */
hide_basemem();
hide_umalloc ( virt_to_phys ( _textdata ), virt_to_phys ( _textdata ) );
hide_textdata();
/* Some really moronic BIOSes bring up the PXE stack via the
* UNDI loader entry point and then don't bother to unload it
* before overwriting the code and data segments. If this
* happens, we really don't want to leave INT 15 hooked,
* because that will cause any loaded OS to die horribly as
* soon as it attempts to fetch the system memory map.
*
* We use a heuristic to guess whether or not we are being
* loaded sensibly.
*/
rm_cs_top = ( ( ( rm_cs << 4 ) + _text16_memsz + 1024 - 1 ) >> 10 );
rm_ds_top = ( ( ( rm_ds << 4 ) + _data16_memsz + 1024 - 1 ) >> 10 );
fbms = get_fbms();
if ( ( rm_cs_top < fbms ) && ( rm_ds_top < fbms ) ) {
DBG ( "Detected potentially unsafe UNDI load at CS=%04x "
"DS=%04x FBMS=%dkB\n", rm_cs, rm_ds, fbms );
DBG ( "Disabling INT 15 memory hiding\n" );
return;
}
/* Hook INT 15 */
hook_bios_interrupt ( 0x15, ( intptr_t ) int15, &int15_vector );
/* Dump memory map after mangling */
DBG ( "Hidden iPXE from system memory map\n" );
get_memmap ( &memmap );
}
/**
* Unhide Etherboot
*
* Uninstalls the INT 15 handler installed by hide_etherboot(), if
* possible.
*/
static void unhide_etherboot ( int flags __unused ) {
struct memory_map memmap;
int rc;
/* 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 ( ( rc = unhook_bios_interrupt ( 0x15, ( intptr_t ) int15,
&int15_vector ) ) != 0 ) {
DBG ( "Cannot unhook INT15: %s\n", strerror ( rc ) );
/* Leave it hooked; there's nothing else we can do,
* and it should be intrinsically safe (though
* wasteful of RAM).
*/
}
/* Unhook fake E820 map, if used */
if ( FAKE_E820 )
unfake_e820();
/* Dump memory map after unhiding */
DBG ( "Unhidden iPXE from system memory map\n" );
get_memmap ( &memmap );
}
/** Hide Etherboot startup function */
struct startup_fn hide_etherboot_startup_fn __startup_fn ( STARTUP_EARLY ) = {
.name = "hidemem",
.startup = hide_etherboot,
.shutdown = unhide_etherboot,
};
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