1 | // SPDX-License-Identifier: GPL-2.0-only |
2 | /* |
3 | * memconsole-coreboot.c |
4 | * |
5 | * Memory based BIOS console accessed through coreboot table. |
6 | * |
7 | * Copyright 2017 Google Inc. |
8 | */ |
9 | |
10 | #include <linux/device.h> |
11 | #include <linux/io.h> |
12 | #include <linux/kernel.h> |
13 | #include <linux/module.h> |
14 | |
15 | #include "memconsole.h" |
16 | #include "coreboot_table.h" |
17 | |
18 | #define CB_TAG_CBMEM_CONSOLE 0x17 |
19 | |
20 | /* CBMEM firmware console log descriptor. */ |
21 | struct cbmem_cons { |
22 | u32 size_dont_access_after_boot; |
23 | u32 cursor; |
24 | u8 body[]; |
25 | } __packed; |
26 | |
27 | #define CURSOR_MASK ((1 << 28) - 1) |
28 | #define OVERFLOW (1 << 31) |
29 | |
30 | static struct cbmem_cons *cbmem_console; |
31 | static u32 cbmem_console_size; |
32 | |
33 | /* |
34 | * The cbmem_console structure is read again on every access because it may |
35 | * change at any time if runtime firmware logs new messages. This may rarely |
36 | * lead to race conditions where the firmware overwrites the beginning of the |
37 | * ring buffer with more lines after we have already read |cursor|. It should be |
38 | * rare and harmless enough that we don't spend extra effort working around it. |
39 | */ |
40 | static ssize_t memconsole_coreboot_read(char *buf, loff_t pos, size_t count) |
41 | { |
42 | u32 cursor = cbmem_console->cursor & CURSOR_MASK; |
43 | u32 flags = cbmem_console->cursor & ~CURSOR_MASK; |
44 | u32 size = cbmem_console_size; |
45 | struct seg { /* describes ring buffer segments in logical order */ |
46 | u32 phys; /* physical offset from start of mem buffer */ |
47 | u32 len; /* length of segment */ |
48 | } seg[2] = { {0}, {0} }; |
49 | size_t done = 0; |
50 | int i; |
51 | |
52 | if (flags & OVERFLOW) { |
53 | if (cursor > size) /* Shouldn't really happen, but... */ |
54 | cursor = 0; |
55 | seg[0] = (struct seg){.phys = cursor, .len = size - cursor}; |
56 | seg[1] = (struct seg){.phys = 0, .len = cursor}; |
57 | } else { |
58 | seg[0] = (struct seg){.phys = 0, .len = min(cursor, size)}; |
59 | } |
60 | |
61 | for (i = 0; i < ARRAY_SIZE(seg) && count > done; i++) { |
62 | done += memory_read_from_buffer(to: buf + done, count: count - done, ppos: &pos, |
63 | from: cbmem_console->body + seg[i].phys, available: seg[i].len); |
64 | pos -= seg[i].len; |
65 | } |
66 | return done; |
67 | } |
68 | |
69 | static int memconsole_probe(struct coreboot_device *dev) |
70 | { |
71 | struct cbmem_cons *tmp_cbmc; |
72 | |
73 | tmp_cbmc = memremap(offset: dev->cbmem_ref.cbmem_addr, |
74 | size: sizeof(*tmp_cbmc), flags: MEMREMAP_WB); |
75 | |
76 | if (!tmp_cbmc) |
77 | return -ENOMEM; |
78 | |
79 | /* Read size only once to prevent overrun attack through /dev/mem. */ |
80 | cbmem_console_size = tmp_cbmc->size_dont_access_after_boot; |
81 | cbmem_console = devm_memremap(dev: &dev->dev, offset: dev->cbmem_ref.cbmem_addr, |
82 | size: cbmem_console_size + sizeof(*cbmem_console), |
83 | flags: MEMREMAP_WB); |
84 | memunmap(addr: tmp_cbmc); |
85 | |
86 | if (IS_ERR(ptr: cbmem_console)) |
87 | return PTR_ERR(ptr: cbmem_console); |
88 | |
89 | memconsole_setup(read_func: memconsole_coreboot_read); |
90 | |
91 | return memconsole_sysfs_init(); |
92 | } |
93 | |
94 | static void memconsole_remove(struct coreboot_device *dev) |
95 | { |
96 | memconsole_exit(); |
97 | } |
98 | |
99 | static const struct coreboot_device_id memconsole_ids[] = { |
100 | { .tag = CB_TAG_CBMEM_CONSOLE }, |
101 | { /* sentinel */ } |
102 | }; |
103 | MODULE_DEVICE_TABLE(coreboot, memconsole_ids); |
104 | |
105 | static struct coreboot_driver memconsole_driver = { |
106 | .probe = memconsole_probe, |
107 | .remove = memconsole_remove, |
108 | .drv = { |
109 | .name = "memconsole" , |
110 | }, |
111 | .id_table = memconsole_ids, |
112 | }; |
113 | module_coreboot_driver(memconsole_driver); |
114 | |
115 | MODULE_AUTHOR("Google, Inc." ); |
116 | MODULE_LICENSE("GPL" ); |
117 | |