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 
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 
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 
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 
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. */
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 
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