IPXE/ipxe-3fe683e/src/arch/x86/interface/pcbios/hidemem.c

   1 /* Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
   2  *
   3  * This program is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU General Public License as
   5  * published by the Free Software Foundation; either version 2 of the
   6  * License, or any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this program; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  16  * 02110-1301, USA.
  17  *
  18  * You can also choose to distribute this program under the terms of
  19  * the Unmodified Binary Distribution Licence (as given in the file
  20  * COPYING.UBDL), provided that you have satisfied its requirements.
  21  */
  22
  23 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  24
  25 #include <assert.h>
  26 #include <realmode.h>
  27 #include <biosint.h>
  28 #include <basemem.h>
  29 #include <fakee820.h>
  30 #include <ipxe/init.h>
  31 #include <ipxe/io.h>
  32 #include <ipxe/hidemem.h>
  33
  34 /** Set to true if you want to test a fake E820 map */
  35 #define FAKE_E820 0
  36
  37 /** Alignment for hidden memory regions */
  38 #define ALIGN_HIDDEN 4096   /* 4kB page alignment should be enough */
  39
  40 /**
  41  * A hidden region of iPXE
  42  *
  43  * This represents a region that will be edited out of the system's
  44  * memory map.
  45  *
  46  * This structure is accessed by assembly code, so must not be
  47  * changed.
  48  */
  49 struct hidden_region {
  50         /** Physical start address */
  51         uint64_t start;
  52         /** Physical end address */
  53         uint64_t end;
  54 };
  55
  56 /** Hidden base memory */
  57 extern struct hidden_region __data16 ( hidemem_base );
  58 #define hidemem_base __use_data16 ( hidemem_base )
  59
  60 /** Hidden umalloc memory */
  61 extern struct hidden_region __data16 ( hidemem_umalloc );
  62 #define hidemem_umalloc __use_data16 ( hidemem_umalloc )
  63
  64 /** Hidden text memory */
  65 extern struct hidden_region __data16 ( hidemem_textdata );
  66 #define hidemem_textdata __use_data16 ( hidemem_textdata )
  67
  68 /** Assembly routine in e820mangler.S */
  69 extern void int15();
  70
  71 /** Vector for storing original INT 15 handler */
  72 extern struct segoff __text16 ( int15_vector );
  73 #define int15_vector __use_text16 ( int15_vector )
  74
  75 /* The linker defines these symbols for us */
  76 extern char _textdata[];
  77 extern char _etextdata[];
  78 extern char _text16_memsz[];
  79 #define _text16_memsz ( ( size_t ) _text16_memsz )
  80 extern char _data16_memsz[];
  81 #define _data16_memsz ( ( size_t ) _data16_memsz )
  82
  83 /**
  84  * Hide region of memory from system memory map
  85  *
  86  * @v region            Hidden memory region
  87  * @v start             Start of region
  88  * @v end               End of region
  89  */
  90 static void hide_region ( struct hidden_region *region,
  91                           physaddr_t start, physaddr_t end ) {
  92
  93         /* Some operating systems get a nasty shock if a region of the
  94          * E820 map seems to start on a non-page boundary.  Make life
  95          * safer by rounding out our edited region.
  96          */
  97         region->start = ( start & ~( ALIGN_HIDDEN - 1 ) );
  98         region->end = ( ( end + ALIGN_HIDDEN - 1 ) & ~( ALIGN_HIDDEN - 1 ) );
  99
 100         DBG ( "Hiding region [%llx,%llx)\n", region->start, region->end );
 101 }
 102
 103 /**
 104  * Hide used base memory
 105  *
 106  */
 107 void hide_basemem ( void ) {
 108         /* Hide from the top of free base memory to 640kB.  Don't use
 109          * hide_region(), because we don't want this rounded to the
 110          * nearest page boundary.
 111          */
 112         hidemem_base.start = ( get_fbms() * 1024 );
 113 }
 114
 115 /**
 116  * Hide umalloc() region
 117  *
 118  */
 119 void hide_umalloc ( physaddr_t start, physaddr_t end ) {
 120         assert ( end <= virt_to_phys ( _textdata ) );
 121         hide_region ( &hidemem_umalloc, start, end );
 122 }
 123
 124 /**
 125  * Hide .text and .data
 126  *
 127  */
 128 void hide_textdata ( void ) {
 129         hide_region ( &hidemem_textdata, virt_to_phys ( _textdata ),
 130                       virt_to_phys ( _etextdata ) );
 131 }
 132
 133 /**
 134  * Hide Etherboot
 135  *
 136  * Installs an INT 15 handler to edit Etherboot out of the memory map
 137  * returned by the BIOS.
 138  */
 139 static void hide_etherboot ( void ) {
 140         struct memory_map memmap;
 141         unsigned int rm_ds_top;
 142         unsigned int rm_cs_top;
 143         unsigned int fbms;
 144
 145         /* Dump memory map before mangling */
 146         DBG ( "Hiding iPXE from system memory map\n" );
 147         get_memmap ( &memmap );
 148
 149         /* Hook in fake E820 map, if we're testing one */
 150         if ( FAKE_E820 ) {
 151                 DBG ( "Hooking in fake E820 map\n" );
 152                 fake_e820();
 153                 get_memmap ( &memmap );
 154         }
 155
 156         /* Initialise the hidden regions */
 157         hide_basemem();
 158         hide_umalloc ( virt_to_phys ( _textdata ), virt_to_phys ( _textdata ) );
 159         hide_textdata();
 160
 161         /* Some really moronic BIOSes bring up the PXE stack via the
 162          * UNDI loader entry point and then don't bother to unload it
 163          * before overwriting the code and data segments.  If this
 164          * happens, we really don't want to leave INT 15 hooked,
 165          * because that will cause any loaded OS to die horribly as
 166          * soon as it attempts to fetch the system memory map.
 167          *
 168          * We use a heuristic to guess whether or not we are being
 169          * loaded sensibly.
 170          */
 171         rm_cs_top = ( ( ( rm_cs << 4 ) + _text16_memsz + 1024 - 1 ) >> 10 );
 172         rm_ds_top = ( ( ( rm_ds << 4 ) + _data16_memsz + 1024 - 1 ) >> 10 );
 173         fbms = get_fbms();
 174         if ( ( rm_cs_top < fbms ) && ( rm_ds_top < fbms ) ) {
 175                 DBG ( "Detected potentially unsafe UNDI load at CS=%04x "
 176                       "DS=%04x FBMS=%dkB\n", rm_cs, rm_ds, fbms );
 177                 DBG ( "Disabling INT 15 memory hiding\n" );
 178                 return;
 179         }
 180
 181         /* Hook INT 15 */
 182         hook_bios_interrupt ( 0x15, ( intptr_t ) int15, &int15_vector );
 183
 184         /* Dump memory map after mangling */
 185         DBG ( "Hidden iPXE from system memory map\n" );
 186         get_memmap ( &memmap );
 187 }
 188
 189 /**
 190  * Unhide Etherboot
 191  *
 192  * Uninstalls the INT 15 handler installed by hide_etherboot(), if
 193  * possible.
 194  */
 195 static void unhide_etherboot ( int flags __unused ) {
 196         struct memory_map memmap;
 197         int rc;
 198
 199         /* If we have more than one hooked interrupt at this point, it
 200          * means that some other vector is still hooked, in which case
 201          * we can't safely unhook INT 15 because we need to keep our
 202          * memory protected.  (We expect there to be at least one
 203          * hooked interrupt, because INT 15 itself is still hooked).
 204          */
 205         if ( hooked_bios_interrupts > 1 ) {
 206                 DBG ( "Cannot unhide: %d interrupt vectors still hooked\n",
 207                       hooked_bios_interrupts );
 208                 return;
 209         }
 210
 211         /* Try to unhook INT 15 */
 212         if ( ( rc = unhook_bios_interrupt ( 0x15, ( intptr_t ) int15,
 213                                             &int15_vector ) ) != 0 ) {
 214                 DBG ( "Cannot unhook INT15: %s\n", strerror ( rc ) );
 215                 /* Leave it hooked; there's nothing else we can do,
 216                  * and it should be intrinsically safe (though
 217                  * wasteful of RAM).
 218                  */
 219         }
 220
 221         /* Unhook fake E820 map, if used */
 222         if ( FAKE_E820 )
 223                 unfake_e820();
 224
 225         /* Dump memory map after unhiding */
 226         DBG ( "Unhidden iPXE from system memory map\n" );
 227         get_memmap ( &memmap );
 228 }
 229
 230 /** Hide Etherboot startup function */
 231 struct startup_fn hide_etherboot_startup_fn __startup_fn ( STARTUP_EARLY ) = {
 232         .name = "hidemem",
 233         .startup = hide_etherboot,
 234         .shutdown = unhide_etherboot,
 235 };