1 /*
2 * memconsole-coreboot.c
3 *
4 * Memory based BIOS console accessed through coreboot table.
5 *
6 * Copyright 2017 Google Inc.
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License v2.0 as published by
10 * the Free Software Foundation.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 */
17
18 #include <linux/device.h>
19 #include <linux/kernel.h>
20 #include <linux/module.h>
21
22 #include "memconsole.h"
23 #include "coreboot_table.h"
24
25 #define CB_TAG_CBMEM_CONSOLE 0x17
26
27 /* CBMEM firmware console log descriptor. */
28 struct cbmem_cons {
29 u32 size_dont_access_after_boot;
30 u32 cursor;
31 u8 body[0];
32 } __packed;
33
34 #define CURSOR_MASK ((1 << 28) - 1)
35 #define OVERFLOW (1 << 31)
36
37 static struct cbmem_cons __iomem *cbmem_console;
38 static u32 cbmem_console_size;
39
40 /*
41 * The cbmem_console structure is read again on every access because it may
42 * change at any time if runtime firmware logs new messages. This may rarely
43 * lead to race conditions where the firmware overwrites the beginning of the
44 * ring buffer with more lines after we have already read |cursor|. It should be
45 * rare and harmless enough that we don't spend extra effort working around it.
46 */
memconsole_coreboot_read(char * buf,loff_t pos,size_t count)47 static ssize_t memconsole_coreboot_read(char *buf, loff_t pos, size_t count)
48 {
49 u32 cursor = cbmem_console->cursor & CURSOR_MASK;
50 u32 flags = cbmem_console->cursor & ~CURSOR_MASK;
51 u32 size = cbmem_console_size;
52 struct seg { /* describes ring buffer segments in logical order */
53 u32 phys; /* physical offset from start of mem buffer */
54 u32 len; /* length of segment */
55 } seg[2] = { {0}, {0} };
56 size_t done = 0;
57 int i;
58
59 if (flags & OVERFLOW) {
60 if (cursor > size) /* Shouldn't really happen, but... */
61 cursor = 0;
62 seg[0] = (struct seg){.phys = cursor, .len = size - cursor};
63 seg[1] = (struct seg){.phys = 0, .len = cursor};
64 } else {
65 seg[0] = (struct seg){.phys = 0, .len = min(cursor, size)};
66 }
67
68 for (i = 0; i < ARRAY_SIZE(seg) && count > done; i++) {
69 done += memory_read_from_buffer(buf + done, count - done, &pos,
70 cbmem_console->body + seg[i].phys, seg[i].len);
71 pos -= seg[i].len;
72 }
73 return done;
74 }
75
memconsole_probe(struct coreboot_device * dev)76 static int memconsole_probe(struct coreboot_device *dev)
77 {
78 struct cbmem_cons __iomem *tmp_cbmc;
79
80 tmp_cbmc = memremap(dev->cbmem_ref.cbmem_addr,
81 sizeof(*tmp_cbmc), MEMREMAP_WB);
82
83 if (!tmp_cbmc)
84 return -ENOMEM;
85
86 /* Read size only once to prevent overrun attack through /dev/mem. */
87 cbmem_console_size = tmp_cbmc->size_dont_access_after_boot;
88 cbmem_console = memremap(dev->cbmem_ref.cbmem_addr,
89 cbmem_console_size + sizeof(*cbmem_console),
90 MEMREMAP_WB);
91 memunmap(tmp_cbmc);
92
93 if (!cbmem_console)
94 return -ENOMEM;
95
96 memconsole_setup(memconsole_coreboot_read);
97
98 return memconsole_sysfs_init();
99 }
100
memconsole_remove(struct coreboot_device * dev)101 static int memconsole_remove(struct coreboot_device *dev)
102 {
103 memconsole_exit();
104
105 if (cbmem_console)
106 memunmap(cbmem_console);
107
108 return 0;
109 }
110
111 static struct coreboot_driver memconsole_driver = {
112 .probe = memconsole_probe,
113 .remove = memconsole_remove,
114 .drv = {
115 .name = "memconsole",
116 },
117 .tag = CB_TAG_CBMEM_CONSOLE,
118 };
119
coreboot_memconsole_exit(void)120 static void coreboot_memconsole_exit(void)
121 {
122 coreboot_driver_unregister(&memconsole_driver);
123 }
124
coreboot_memconsole_init(void)125 static int __init coreboot_memconsole_init(void)
126 {
127 return coreboot_driver_register(&memconsole_driver);
128 }
129
130 module_exit(coreboot_memconsole_exit);
131 module_init(coreboot_memconsole_init);
132
133 MODULE_AUTHOR("Google, Inc.");
134 MODULE_LICENSE("GPL");
135
