1 /*
2 * Linux Boot Option ROM for fw_cfg DMA
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, see <http://www.gnu.org/licenses/>.
16 *
17 * Copyright (c) 2015-2016 Red Hat Inc.
18 * Authors:
19 * Marc Marí <marc.mari.barcelo@gmail.com>
20 * Richard W.M. Jones <rjones@redhat.com>
21 */
22
23 asm(
24 ".text\n"
25 ".global _start\n"
26 "_start:\n"
27 " .short 0xaa55\n"
28 " .byte 3\n" /* desired size in 512 units; signrom.py adds padding */
29 " .byte 0xcb\n" /* far return without prefix */
30 " .org 0x18\n"
31 " .short 0\n"
32 " .short _pnph\n"
33 "_pnph:\n"
34 " .ascii \"$PnP\"\n"
35 " .byte 0x01\n"
36 " .byte (_pnph_len / 16)\n"
37 " .short 0x0000\n"
38 " .byte 0x00\n"
39 " .byte 0x00\n"
40 " .long 0x00000000\n"
41 " .short _manufacturer\n"
42 " .short _product\n"
43 " .long 0x00000000\n"
44 " .short 0x0000\n"
45 " .short 0x0000\n"
46 " .short _bev\n"
47 " .short 0x0000\n"
48 " .short 0x0000\n"
49 " .equ _pnph_len, . - _pnph\n"
50 "_manufacturer:\n"
51 " .asciz \"QEMU\"\n"
52 "_product:\n"
53 " .asciz \"Linux loader DMA\"\n"
54 " .align 4, 0\n"
55 "_bev:\n"
56 " cli\n"
57 " cld\n"
58 " jmp load_kernel\n"
59 );
60
61 /*
62 * The includes of C headers must be after the asm block to avoid compiler
63 * errors.
64 */
65 #include <stdint.h>
66 #include "optrom.h"
67 #include "optrom_fw_cfg.h"
68
set_es(void * addr)69 static inline void set_es(void *addr)
70 {
71 uint32_t seg = (uint32_t)addr >> 4;
72 asm("movl %0, %%es" : : "r"(seg));
73 }
74
readw_es(uint16_t offset)75 static inline uint16_t readw_es(uint16_t offset)
76 {
77 uint16_t val;
78 asm(ADDR32 "movw %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset));
79 barrier();
80 return val;
81 }
82
readl_es(uint16_t offset)83 static inline uint32_t readl_es(uint16_t offset)
84 {
85 uint32_t val;
86 asm(ADDR32 "movl %%es:(%1), %0" : "=r"(val) : "r"((uint32_t)offset));
87 barrier();
88 return val;
89 }
90
writel_es(uint16_t offset,uint32_t val)91 static inline void writel_es(uint16_t offset, uint32_t val)
92 {
93 barrier();
94 asm(ADDR32 "movl %0, %%es:(%1)" : : "r"(val), "r"((uint32_t)offset));
95 }
96
97 /* Return top of memory using BIOS function E801. */
get_e801_addr(void)98 static uint32_t get_e801_addr(void)
99 {
100 uint16_t ax, bx, cx, dx;
101 uint32_t ret;
102
103 asm("int $0x15\n"
104 : "=a"(ax), "=b"(bx), "=c"(cx), "=d"(dx)
105 : "a"(0xe801), "b"(0), "c"(0), "d"(0));
106
107 /* Not SeaBIOS, but in theory a BIOS could return CX=DX=0 in which
108 * case we need to use the result from AX & BX instead.
109 */
110 if (cx == 0 && dx == 0) {
111 cx = ax;
112 dx = bx;
113 }
114
115 if (dx) {
116 /* DX = extended memory above 16M, in 64K units.
117 * Convert it to bytes and return.
118 */
119 ret = ((uint32_t)dx + 256 /* 16M in 64K units */) << 16;
120 } else {
121 /* This is a fallback path for machines with <= 16MB of RAM,
122 * which probably would never be the case, but deal with it
123 * anyway.
124 *
125 * CX = extended memory between 1M and 16M, in kilobytes
126 * Convert it to bytes and return.
127 */
128 ret = ((uint32_t)cx + 1024 /* 1M in K */) << 10;
129 }
130
131 return ret;
132 }
133
134 /* Force the asm name without leading underscore, even on Win32. */
135 extern void load_kernel(void) asm("load_kernel");
136
load_kernel(void)137 void load_kernel(void)
138 {
139 void *setup_addr;
140 void *initrd_addr;
141 void *kernel_addr;
142 void *cmdline_addr;
143 uint32_t setup_size;
144 uint32_t initrd_size;
145 uint32_t kernel_size;
146 uint32_t cmdline_size;
147 uint32_t initrd_end_page, max_allowed_page;
148 uint32_t segment_addr, stack_addr;
149
150 bios_cfg_read_entry_dma(&setup_addr, FW_CFG_SETUP_ADDR, 4);
151 bios_cfg_read_entry_dma(&setup_size, FW_CFG_SETUP_SIZE, 4);
152 bios_cfg_read_entry_dma(setup_addr, FW_CFG_SETUP_DATA, setup_size);
153
154 set_es(setup_addr);
155
156 /* For protocol < 0x203 we don't have initrd_max ... */
157 if (readw_es(0x206) < 0x203) {
158 /* ... so we assume initrd_max = 0x37ffffff. */
159 writel_es(0x22c, 0x37ffffff);
160 }
161
162 bios_cfg_read_entry_dma(&initrd_addr, FW_CFG_INITRD_ADDR, 4);
163 bios_cfg_read_entry_dma(&initrd_size, FW_CFG_INITRD_SIZE, 4);
164
165 initrd_end_page = ((uint32_t)(initrd_addr + initrd_size) & -4096);
166 max_allowed_page = (readl_es(0x22c) & -4096);
167
168 if (initrd_end_page != 0 && max_allowed_page != 0 &&
169 initrd_end_page != max_allowed_page) {
170 /* Initrd at the end of memory. Compute better initrd address
171 * based on e801 data
172 */
173 initrd_addr = (void *)((get_e801_addr() - initrd_size) & -4096);
174 writel_es(0x218, (uint32_t)initrd_addr);
175
176 }
177
178 bios_cfg_read_entry_dma(initrd_addr, FW_CFG_INITRD_DATA, initrd_size);
179
180 bios_cfg_read_entry_dma(&kernel_addr, FW_CFG_KERNEL_ADDR, 4);
181 bios_cfg_read_entry_dma(&kernel_size, FW_CFG_KERNEL_SIZE, 4);
182 bios_cfg_read_entry_dma(kernel_addr, FW_CFG_KERNEL_DATA, kernel_size);
183
184 bios_cfg_read_entry_dma(&cmdline_addr, FW_CFG_CMDLINE_ADDR, 4);
185 bios_cfg_read_entry_dma(&cmdline_size, FW_CFG_CMDLINE_SIZE, 4);
186 bios_cfg_read_entry_dma(cmdline_addr, FW_CFG_CMDLINE_DATA, cmdline_size);
187
188 /* Boot linux */
189 segment_addr = ((uint32_t)setup_addr >> 4);
190 stack_addr = (uint32_t)(cmdline_addr - setup_addr - 16);
191
192 /* As we are changing critical registers, we cannot leave freedom to the
193 * compiler.
194 */
195 asm("movw %%ax, %%ds\n"
196 "movw %%ax, %%es\n"
197 "movw %%ax, %%fs\n"
198 "movw %%ax, %%gs\n"
199 "movw %%ax, %%ss\n"
200 "movl %%ebx, %%esp\n"
201 "addw $0x20, %%ax\n"
202 "pushw %%ax\n" /* CS */
203 "pushw $0\n" /* IP */
204 /* Clear registers and jump to Linux */
205 "xor %%ebx, %%ebx\n"
206 "xor %%ecx, %%ecx\n"
207 "xor %%edx, %%edx\n"
208 "xor %%edi, %%edi\n"
209 "xor %%ebp, %%ebp\n"
210 "lretw\n"
211 : : "a"(segment_addr), "b"(stack_addr));
212 }
213