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longpanda
238
IPXE/ipxe-3fe683e/src/arch/x86/interface/pcbios/hidemem.c
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238
IPXE/ipxe-3fe683e/src/arch/x86/interface/pcbios/hidemem.c
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/* Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*
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* You can also choose to distribute this program under the terms of
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* the Unmodified Binary Distribution Licence (as given in the file
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* COPYING.UBDL), provided that you have satisfied its requirements.
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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#include <assert.h>
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#include <realmode.h>
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#include <biosint.h>
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#include <basemem.h>
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#include <fakee820.h>
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#include <ipxe/init.h>
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#include <ipxe/io.h>
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#include <ipxe/hidemem.h>
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/** Set to true if you want to test a fake E820 map */
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#define FAKE_E820 0
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/** Alignment for hidden memory regions */
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#define ALIGN_HIDDEN 4096 /* 4kB page alignment should be enough */
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/**
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* A hidden region of iPXE
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*
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* This represents a region that will be edited out of the system's
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* memory map.
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*
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* This structure is accessed by assembly code, so must not be
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* changed.
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*/
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struct hidden_region {
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/** Physical start address */
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uint64_t start;
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/** Physical end address */
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uint64_t end;
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};
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/** Hidden base memory */
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extern struct hidden_region __data16 ( hidemem_base );
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#define hidemem_base __use_data16 ( hidemem_base )
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/** Hidden umalloc memory */
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extern struct hidden_region __data16 ( hidemem_umalloc );
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#define hidemem_umalloc __use_data16 ( hidemem_umalloc )
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/** Hidden text memory */
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extern struct hidden_region __data16 ( hidemem_textdata );
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#define hidemem_textdata __use_data16 ( hidemem_textdata )
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/** Assembly routine in e820mangler.S */
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extern void int15();
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/** Vector for storing original INT 15 handler */
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extern struct segoff __text16 ( int15_vector );
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#define int15_vector __use_text16 ( int15_vector )
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/* The linker defines these symbols for us */
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extern char _textdata[];
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extern char _etextdata[];
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extern char _text16_memsz[];
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#define _text16_memsz ( ( size_t ) _text16_memsz )
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extern char _data16_memsz[];
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#define _data16_memsz ( ( size_t ) _data16_memsz )
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/**
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* Hide region of memory from system memory map
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*
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* @v region Hidden memory region
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* @v start Start of region
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* @v end End of region
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*/
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static void hide_region ( struct hidden_region *region,
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physaddr_t start, physaddr_t end ) {
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/* Some operating systems get a nasty shock if a region of the
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* E820 map seems to start on a non-page boundary. Make life
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* safer by rounding out our edited region.
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*/
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region->start = ( start & ~( ALIGN_HIDDEN - 1 ) );
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region->end = ( ( end + ALIGN_HIDDEN - 1 ) & ~( ALIGN_HIDDEN - 1 ) );
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DBG ( "Hiding region [%llx,%llx)\n", region->start, region->end );
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}
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/**
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* Hide used base memory
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*
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*/
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void hide_basemem ( void ) {
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/* Hide from the top of free base memory to 640kB. Don't use
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* hide_region(), because we don't want this rounded to the
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* nearest page boundary.
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*/
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hidemem_base.start = ( get_fbms() * 1024 );
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}
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/**
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* Hide umalloc() region
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*
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*/
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void hide_umalloc ( physaddr_t start, physaddr_t end ) {
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assert ( end <= virt_to_phys ( _textdata ) );
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hide_region ( &hidemem_umalloc, start, end );
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}
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/**
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* Hide .text and .data
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*
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*/
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void hide_textdata ( void ) {
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/* Deleted by longpanda */
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#if 0
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hide_region ( &hidemem_textdata, virt_to_phys ( _textdata ),
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virt_to_phys ( _etextdata ) );
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#endif
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}
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/**
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* Hide Etherboot
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*
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* Installs an INT 15 handler to edit Etherboot out of the memory map
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* returned by the BIOS.
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*/
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static void hide_etherboot ( void ) {
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struct memory_map memmap;
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unsigned int rm_ds_top;
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unsigned int rm_cs_top;
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unsigned int fbms;
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/* Dump memory map before mangling */
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DBG ( "Hiding iPXE from system memory map\n" );
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get_memmap ( &memmap );
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/* Hook in fake E820 map, if we're testing one */
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if ( FAKE_E820 ) {
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DBG ( "Hooking in fake E820 map\n" );
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fake_e820();
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get_memmap ( &memmap );
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}
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/* Initialise the hidden regions */
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hide_basemem();
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hide_umalloc ( virt_to_phys ( _textdata ), virt_to_phys ( _textdata ) );
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hide_textdata();
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/* Some really moronic BIOSes bring up the PXE stack via the
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* UNDI loader entry point and then don't bother to unload it
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* before overwriting the code and data segments. If this
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* happens, we really don't want to leave INT 15 hooked,
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* because that will cause any loaded OS to die horribly as
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* soon as it attempts to fetch the system memory map.
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*
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* We use a heuristic to guess whether or not we are being
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* loaded sensibly.
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*/
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rm_cs_top = ( ( ( rm_cs << 4 ) + _text16_memsz + 1024 - 1 ) >> 10 );
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rm_ds_top = ( ( ( rm_ds << 4 ) + _data16_memsz + 1024 - 1 ) >> 10 );
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fbms = get_fbms();
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if ( ( rm_cs_top < fbms ) && ( rm_ds_top < fbms ) ) {
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DBG ( "Detected potentially unsafe UNDI load at CS=%04x "
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"DS=%04x FBMS=%dkB\n", rm_cs, rm_ds, fbms );
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DBG ( "Disabling INT 15 memory hiding\n" );
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return;
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}
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/* Hook INT 15 */
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hook_bios_interrupt ( 0x15, ( intptr_t ) int15, &int15_vector );
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/* Dump memory map after mangling */
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DBG ( "Hidden iPXE from system memory map\n" );
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get_memmap ( &memmap );
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}
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/**
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* Unhide Etherboot
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*
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* Uninstalls the INT 15 handler installed by hide_etherboot(), if
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* possible.
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*/
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static void unhide_etherboot ( int flags __unused ) {
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struct memory_map memmap;
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int rc;
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/* If we have more than one hooked interrupt at this point, it
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* means that some other vector is still hooked, in which case
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* we can't safely unhook INT 15 because we need to keep our
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* memory protected. (We expect there to be at least one
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* hooked interrupt, because INT 15 itself is still hooked).
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*/
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if ( hooked_bios_interrupts > 1 ) {
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DBG ( "Cannot unhide: %d interrupt vectors still hooked\n",
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hooked_bios_interrupts );
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return;
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}
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/* Try to unhook INT 15 */
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if ( ( rc = unhook_bios_interrupt ( 0x15, ( intptr_t ) int15,
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&int15_vector ) ) != 0 ) {
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DBG ( "Cannot unhook INT15: %s\n", strerror ( rc ) );
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/* Leave it hooked; there's nothing else we can do,
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* and it should be intrinsically safe (though
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* wasteful of RAM).
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*/
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}
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/* Unhook fake E820 map, if used */
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if ( FAKE_E820 )
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unfake_e820();
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/* Dump memory map after unhiding */
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DBG ( "Unhidden iPXE from system memory map\n" );
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get_memmap ( &memmap );
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}
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/** Hide Etherboot startup function */
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struct startup_fn hide_etherboot_startup_fn __startup_fn ( STARTUP_EARLY ) = {
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.name = "hidemem",
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.startup = hide_etherboot,
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.shutdown = unhide_etherboot,
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};
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