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/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. */
  21struct 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
  30static struct cbmem_cons *cbmem_console;
  31static 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 */
  40static 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(buf + done, count - done, &pos,
  63                        cbmem_console->body + seg[i].phys, seg[i].len);
  64                pos -= seg[i].len;
  65        }
  66        return done;
  67}
  68
  69static int memconsole_probe(struct coreboot_device *dev)
  70{
  71        struct cbmem_cons *tmp_cbmc;
  72
  73        tmp_cbmc = memremap(dev->cbmem_ref.cbmem_addr,
  74                            sizeof(*tmp_cbmc), 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->cbmem_ref.cbmem_addr,
  82                                 cbmem_console_size + sizeof(*cbmem_console),
  83                                 MEMREMAP_WB);
  84        memunmap(tmp_cbmc);
  85
  86        if (IS_ERR(cbmem_console))
  87                return PTR_ERR(cbmem_console);
  88
  89        memconsole_setup(memconsole_coreboot_read);
  90
  91        return memconsole_sysfs_init();
  92}
  93
  94static void memconsole_remove(struct coreboot_device *dev)
  95{
  96        memconsole_exit();
  97}
  98
  99static struct coreboot_driver memconsole_driver = {
 100        .probe = memconsole_probe,
 101        .remove = memconsole_remove,
 102        .drv = {
 103                .name = "memconsole",
 104        },
 105        .tag = CB_TAG_CBMEM_CONSOLE,
 106};
 107module_coreboot_driver(memconsole_driver);
 108
 109MODULE_AUTHOR("Google, Inc.");
 110MODULE_LICENSE("GPL");
 111