LXR linux/drivers/firmware/google/memconsole-coreboot.c

   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/kernel.h>
  12#include <linux/module.h>
  13
  14#include "memconsole.h"
  15#include "coreboot_table.h"
  16
  17#define CB_TAG_CBMEM_CONSOLE    0x17
  18
  19/* CBMEM firmware console log descriptor. */
  20struct cbmem_cons {
  21        u32 size_dont_access_after_boot;
  22        u32 cursor;
  23        u8  body[0];
  24} __packed;
  25
  26#define CURSOR_MASK ((1 << 28) - 1)
  27#define OVERFLOW (1 << 31)
  28
  29static struct cbmem_cons __iomem *cbmem_console;
  30static u32 cbmem_console_size;
  31
  32/*
  33 * The cbmem_console structure is read again on every access because it may
  34 * change at any time if runtime firmware logs new messages. This may rarely
  35 * lead to race conditions where the firmware overwrites the beginning of the
  36 * ring buffer with more lines after we have already read |cursor|. It should be
  37 * rare and harmless enough that we don't spend extra effort working around it.
  38 */
  39static ssize_t memconsole_coreboot_read(char *buf, loff_t pos, size_t count)
  40{
  41        u32 cursor = cbmem_console->cursor & CURSOR_MASK;
  42        u32 flags = cbmem_console->cursor & ~CURSOR_MASK;
  43        u32 size = cbmem_console_size;
  44        struct seg {    /* describes ring buffer segments in logical order */
  45                u32 phys;       /* physical offset from start of mem buffer */
  46                u32 len;        /* length of segment */
  47        } seg[2] = { {0}, {0} };
  48        size_t done = 0;
  49        int i;
  50
  51        if (flags & OVERFLOW) {
  52                if (cursor > size)      /* Shouldn't really happen, but... */
  53                        cursor = 0;
  54                seg[0] = (struct seg){.phys = cursor, .len = size - cursor};
  55                seg[1] = (struct seg){.phys = 0, .len = cursor};
  56        } else {
  57                seg[0] = (struct seg){.phys = 0, .len = min(cursor, size)};
  58        }
  59
  60        for (i = 0; i < ARRAY_SIZE(seg) && count > done; i++) {
  61                done += memory_read_from_buffer(buf + done, count - done, &pos,
  62                        cbmem_console->body + seg[i].phys, seg[i].len);
  63                pos -= seg[i].len;
  64        }
  65        return done;
  66}
  67
  68static int memconsole_probe(struct coreboot_device *dev)
  69{
  70        struct cbmem_cons __iomem *tmp_cbmc;
  71
  72        tmp_cbmc = memremap(dev->cbmem_ref.cbmem_addr,
  73                            sizeof(*tmp_cbmc), MEMREMAP_WB);
  74
  75        if (!tmp_cbmc)
  76                return -ENOMEM;
  77
  78        /* Read size only once to prevent overrun attack through /dev/mem. */
  79        cbmem_console_size = tmp_cbmc->size_dont_access_after_boot;
  80        cbmem_console = memremap(dev->cbmem_ref.cbmem_addr,
  81                                 cbmem_console_size + sizeof(*cbmem_console),
  82                                 MEMREMAP_WB);
  83        memunmap(tmp_cbmc);
  84
  85        if (!cbmem_console)
  86                return -ENOMEM;
  87
  88        memconsole_setup(memconsole_coreboot_read);
  89
  90        return memconsole_sysfs_init();
  91}
  92
  93static int memconsole_remove(struct coreboot_device *dev)
  94{
  95        memconsole_exit();
  96
  97        if (cbmem_console)
  98                memunmap(cbmem_console);
  99
 100        return 0;
 101}
 102
 103static struct coreboot_driver memconsole_driver = {
 104        .probe = memconsole_probe,
 105        .remove = memconsole_remove,
 106        .drv = {
 107                .name = "memconsole",
 108        },
 109        .tag = CB_TAG_CBMEM_CONSOLE,
 110};
 111
 112static void coreboot_memconsole_exit(void)
 113{
 114        coreboot_driver_unregister(&memconsole_driver);
 115}
 116
 117static int __init coreboot_memconsole_init(void)
 118{
 119        return coreboot_driver_register(&memconsole_driver);
 120}
 121
 122module_exit(coreboot_memconsole_exit);
 123module_init(coreboot_memconsole_init);
 124
 125MODULE_AUTHOR("Google, Inc.");
 126MODULE_LICENSE("GPL");
 127