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., 675 Mass Ave, Cambridge, MA 02139, USA.
16 */
17
18 FILE_LICENCE ( GPL2_OR_LATER );
19
20 #include <assert.h>
21 #include <realmode.h>
22 #include <biosint.h>
23 #include <basemem.h>
24 #include <fakee820.h>
25 #include <gpxe/init.h>
26 #include <gpxe/memmap.h>
27 #include <gpxe/hidemem.h>
28
29 /** Set to true if you want to test a fake E820 map */
30 #define FAKE_E820 0
31
32 /** Alignment for hidden memory regions */
33 #define ALIGN_HIDDEN 4096 /* 4kB page alignment should be enough */
34
35 /**
36 * A hidden region of gPXE
37 *
38 * This represents a region that will be edited out of the system's
39 * memory map.
40 *
41 * This structure is accessed by assembly code, so must not be
42 * changed.
43 */
44 struct hidden_region {
45 /** Physical start address */
46 uint64_t start;
47 /** Physical end address */
48 uint64_t end;
49 };
50
51 /** Hidden base memory */
52 extern struct hidden_region __data16 ( hidemem_base );
53 #define hidemem_base __use_data16 ( hidemem_base )
54
55 /** Hidden umalloc memory */
56 extern struct hidden_region __data16 ( hidemem_umalloc );
57 #define hidemem_umalloc __use_data16 ( hidemem_umalloc )
58
59 /** Hidden text memory */
60 extern struct hidden_region __data16 ( hidemem_textdata );
61 #define hidemem_textdata __use_data16 ( hidemem_textdata )
62
63 /** Assembly routine in e820mangler.S */
64 extern void int15();
65
66 /** Vector for storing original INT 15 handler */
67 extern struct segoff __text16 ( int15_vector );
68 #define int15_vector __use_text16 ( int15_vector )
69
70 /* The linker defines these symbols for us */
71 extern char _textdata[];
72 extern char _etextdata[];
73 extern char _text16_memsz[];
74 #define _text16_memsz ( ( unsigned int ) _text16_memsz )
75 extern char _data16_memsz[];
76 #define _data16_memsz ( ( unsigned int ) _data16_memsz )
77
78 /**
79 * Hide region of memory from system memory map
80 *
81 * @v region Hidden memory region
82 * @v start Start of region
83 * @v end End of region
84 */
hide_region(struct hidden_region * region,physaddr_t start,physaddr_t end)85 static void hide_region ( struct hidden_region *region,
86 physaddr_t start, physaddr_t end ) {
87
88 /* Some operating systems get a nasty shock if a region of the
89 * E820 map seems to start on a non-page boundary. Make life
90 * safer by rounding out our edited region.
91 */
92 region->start = ( start & ~( ALIGN_HIDDEN - 1 ) );
93 region->end = ( ( end + ALIGN_HIDDEN - 1 ) & ~( ALIGN_HIDDEN - 1 ) );
94
95 DBG ( "Hiding region [%llx,%llx)\n", region->start, region->end );
96 }
97
98 /**
99 * Hide used base memory
100 *
101 */
hide_basemem(void)102 void hide_basemem ( void ) {
103 /* Hide from the top of free base memory to 640kB. Don't use
104 * hide_region(), because we don't want this rounded to the
105 * nearest page boundary.
106 */
107 hidemem_base.start = ( get_fbms() * 1024 );
108 }
109
110 /**
111 * Hide umalloc() region
112 *
113 */
hide_umalloc(physaddr_t start,physaddr_t end)114 void hide_umalloc ( physaddr_t start, physaddr_t end ) {
115 assert ( end <= virt_to_phys ( _textdata ) );
116 hide_region ( &hidemem_umalloc, start, end );
117 }
118
119 /**
120 * Hide .text and .data
121 *
122 */
hide_textdata(void)123 void hide_textdata ( void ) {
124 hide_region ( &hidemem_textdata, virt_to_phys ( _textdata ),
125 virt_to_phys ( _etextdata ) );
126 }
127
128 /**
129 * Hide Etherboot
130 *
131 * Installs an INT 15 handler to edit Etherboot out of the memory map
132 * returned by the BIOS.
133 */
hide_etherboot(void)134 static void hide_etherboot ( void ) {
135 struct memory_map memmap;
136 unsigned int rm_ds_top;
137 unsigned int rm_cs_top;
138 unsigned int fbms;
139
140 /* Dump memory map before mangling */
141 DBG ( "Hiding gPXE from system memory map\n" );
142 get_memmap ( &memmap );
143
144 /* Hook in fake E820 map, if we're testing one */
145 if ( FAKE_E820 ) {
146 DBG ( "Hooking in fake E820 map\n" );
147 fake_e820();
148 get_memmap ( &memmap );
149 }
150
151 /* Initialise the hidden regions */
152 hide_basemem();
153 hide_umalloc ( virt_to_phys ( _textdata ), virt_to_phys ( _textdata ) );
154 hide_textdata();
155
156 /* Some really moronic BIOSes bring up the PXE stack via the
157 * UNDI loader entry point and then don't bother to unload it
158 * before overwriting the code and data segments. If this
159 * happens, we really don't want to leave INT 15 hooked,
160 * because that will cause any loaded OS to die horribly as
161 * soon as it attempts to fetch the system memory map.
162 *
163 * We use a heuristic to guess whether or not we are being
164 * loaded sensibly.
165 */
166 rm_cs_top = ( ( ( rm_cs << 4 ) + _text16_memsz + 1024 - 1 ) >> 10 );
167 rm_ds_top = ( ( ( rm_ds << 4 ) + _data16_memsz + 1024 - 1 ) >> 10 );
168 fbms = get_fbms();
169 if ( ( rm_cs_top < fbms ) && ( rm_ds_top < fbms ) ) {
170 DBG ( "Detected potentially unsafe UNDI load at CS=%04x "
171 "DS=%04x FBMS=%dkB\n", rm_cs, rm_ds, fbms );
172 DBG ( "Disabling INT 15 memory hiding\n" );
173 return;
174 }
175
176 /* Hook INT 15 */
177 hook_bios_interrupt ( 0x15, ( unsigned int ) int15,
178 &int15_vector );
179
180 /* Dump memory map after mangling */
181 DBG ( "Hidden gPXE from system memory map\n" );
182 get_memmap ( &memmap );
183 }
184
185 /**
186 * Unhide Etherboot
187 *
188 * Uninstalls the INT 15 handler installed by hide_etherboot(), if
189 * possible.
190 */
unhide_etherboot(int flags __unused)191 static void unhide_etherboot ( int flags __unused ) {
192
193 /* If we have more than one hooked interrupt at this point, it
194 * means that some other vector is still hooked, in which case
195 * we can't safely unhook INT 15 because we need to keep our
196 * memory protected. (We expect there to be at least one
197 * hooked interrupt, because INT 15 itself is still hooked).
198 */
199 if ( hooked_bios_interrupts > 1 ) {
200 DBG ( "Cannot unhide: %d interrupt vectors still hooked\n",
201 hooked_bios_interrupts );
202 return;
203 }
204
205 /* Try to unhook INT 15. If it fails, then just leave it
206 * hooked; it takes care of protecting itself. :)
207 */
208 unhook_bios_interrupt ( 0x15, ( unsigned int ) int15,
209 &int15_vector );
210
211 /* Unhook fake E820 map, if used */
212 if ( FAKE_E820 )
213 unfake_e820();
214 }
215
216 /** Hide Etherboot startup function */
217 struct startup_fn hide_etherboot_startup_fn __startup_fn ( STARTUP_EARLY ) = {
218 .startup = hide_etherboot,
219 .shutdown = unhide_etherboot,
220 };
221