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/kernel.h> 19 #include <linux/module.h> 20 #include <linux/platform_device.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 */ 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 76 static int memconsole_coreboot_init(phys_addr_t physaddr) 77 { 78 struct cbmem_cons __iomem *tmp_cbmc; 79 80 tmp_cbmc = memremap(physaddr, sizeof(*tmp_cbmc), MEMREMAP_WB); 81 82 if (!tmp_cbmc) 83 return -ENOMEM; 84 85 /* Read size only once to prevent overrun attack through /dev/mem. */ 86 cbmem_console_size = tmp_cbmc->size_dont_access_after_boot; 87 cbmem_console = memremap(physaddr, 88 cbmem_console_size + sizeof(*cbmem_console), 89 MEMREMAP_WB); 90 memunmap(tmp_cbmc); 91 92 if (!cbmem_console) 93 return -ENOMEM; 94 95 memconsole_setup(memconsole_coreboot_read); 96 return 0; 97 } 98 99 static int memconsole_probe(struct platform_device *pdev) 100 { 101 int ret; 102 struct lb_cbmem_ref entry; 103 104 ret = coreboot_table_find(CB_TAG_CBMEM_CONSOLE, &entry, sizeof(entry)); 105 if (ret) 106 return ret; 107 108 ret = memconsole_coreboot_init(entry.cbmem_addr); 109 if (ret) 110 return ret; 111 112 return memconsole_sysfs_init(); 113 } 114 115 static int memconsole_remove(struct platform_device *pdev) 116 { 117 memconsole_exit(); 118 119 if (cbmem_console) 120 memunmap(cbmem_console); 121 122 return 0; 123 } 124 125 static struct platform_driver memconsole_driver = { 126 .probe = memconsole_probe, 127 .remove = memconsole_remove, 128 .driver = { 129 .name = "memconsole", 130 }, 131 }; 132 133 static int __init platform_memconsole_init(void) 134 { 135 struct platform_device *pdev; 136 137 pdev = platform_device_register_simple("memconsole", -1, NULL, 0); 138 if (IS_ERR(pdev)) 139 return PTR_ERR(pdev); 140 141 platform_driver_register(&memconsole_driver); 142 143 return 0; 144 } 145 146 module_init(platform_memconsole_init); 147 148 MODULE_AUTHOR("Google, Inc."); 149 MODULE_LICENSE("GPL"); 150