SchOS/kernel/dev/dmi.c

// SPDX-License-Identifier: GPL-2.0-or-later
//
// SMBIOS: what the firmware says this machine is.
//
// Vendor, model, board and firmware version live nowhere else. ACPI describes
// the hardware's wiring and PCI its parts, but "Lenovo 20XW / ThinkPad X1
// Carbon Gen 9, BIOS N32ET75W" is only in this table, and it is the first line
// anybody asks for about a machine that will not boot. Linux prints it as the
// "DMI:" line of its log and publishes the fields in /sys/class/dmi/id; this
// does both, under the same names.
//
// Written from the DMTF's SMBIOS specification (DSP0134). The entry point is
// handed over by the UEFI loader from the configuration table, or found by the
// BIOS-era scan of 0xF0000-0xFFFFF when it was not.

#include "types.h"
#include "defs.h"
#include "memlayout.h"
#include "schboot.h"
#include "hwinfo.h"

static int    tried;
static uint64 ep_pa;  static uint32 ep_len;
static uint64 tab_pa; static uint32 tab_len;
static const uint8 *tab;                    // mapped, or 0

const char *const dmi_field_names[DMI_NFIELDS] = {
  [DMI_BIOS_VENDOR]     = "bios_vendor",
  [DMI_BIOS_VERSION]    = "bios_version",
  [DMI_BIOS_DATE]       = "bios_date",
  [DMI_BIOS_RELEASE]    = "bios_release",
  [DMI_SYS_VENDOR]      = "sys_vendor",
  [DMI_PRODUCT_NAME]    = "product_name",
  [DMI_PRODUCT_VERSION] = "product_version",
  [DMI_PRODUCT_SKU]     = "product_sku",
  [DMI_PRODUCT_FAMILY]  = "product_family",
  [DMI_BOARD_VENDOR]    = "board_vendor",
  [DMI_BOARD_NAME]      = "board_name",
  [DMI_BOARD_VERSION]   = "board_version",
  [DMI_CHASSIS_VENDOR]  = "chassis_vendor",
  [DMI_CHASSIS_TYPE]    = "chassis_type",
  [DMI_CHASSIS_VERSION] = "chassis_version",
};

void *
phys_view(uint64 pa, uint64 len)
{
  if (pa + len <= 4ULL * 1024 * 1024 * 1024)
    return P2V(pa);
  return ioremap(pa, len);
}

int
boot_is_efi(void)
{
  return *(uint32 *)P2V(SCHBOOT_EFI_FLAG) == SCHBOOT_EFI_MAGIC;
}

static int
sum_ok(const uint8 *p, uint32 n)
{
  uint8 s = 0;
  while (n--)
    s += *p++;
  return s == 0;
}

// One entry point at `pa`, either kind. Sets the table on success.
static int
try_entry(uint64 pa)
{
  const uint8 *e = phys_view(pa, 32);
  if (e == 0)
    return 0;

  if (memcmp(e, "_SM3_", 5) == 0) {
    uint32 n = e[6];
    if (n < 24 || n > 32 || !sum_ok(e, n))
      return 0;
    ep_len  = n;
    tab_len = *(uint32 *)(e + 0x0C);        // the most it can be
    tab_pa  = *(uint64 *)(e + 0x10);
  } else if (memcmp(e, "_SM_", 4) == 0) {
    uint32 n = e[5];
    if (n < 0x1F || n > 32 || !sum_ok(e, n) || memcmp(e + 0x10, "_DMI_", 5))
      return 0;
    ep_len  = n;
    tab_len = *(uint16 *)(e + 0x16);
    tab_pa  = *(uint32 *)(e + 0x18);
  } else {
    return 0;
  }
  // A table that large is not one; a firmware bug, and walking it would be
  // walking whatever memory follows.
  if (tab_pa == 0 || tab_len == 0 || tab_len > 1024 * 1024)
    return 0;
  ep_pa = pa;
  return 1;
}

static void
find(void)
{
  if (tried)
    return;
  tried = 1;

  uint64 handed = *(uint64 *)P2V(SCHBOOT_SMBIOS_ADDR);
  int ok = boot_is_efi() && handed && try_entry(handed);

  // The BIOS convention: 16-byte aligned somewhere in the last 64 KB below
  // 1 MB. The 64-bit kind first, as Linux prefers it.
  for (int pass = 0; !ok && pass < 2; pass++)
    for (uint64 a = 0xF0000; !ok && a < 0x100000; a += 16) {
      const char *p = (const char *)P2V(a);
      if (memcmp(p, pass == 0 ? "_SM3_" : "_SM_", pass == 0 ? 5 : 4) == 0)
        ok = try_entry(a);
    }
  if (!ok) {
    ep_pa = tab_pa = 0;
    return;
  }
  tab = phys_view(tab_pa, tab_len);
}

int
dmi_entry(uint64 *pa, uint32 *len)
{
  find();
  if (ep_pa == 0)
    return -1;
  *pa = ep_pa;
  *len = ep_len;
  return 0;
}

// The real length: up to and including the end-of-table structure, which for
// SMBIOS 3 is less than the maximum the entry point gave.
int
dmi_table(uint64 *pa, uint32 *len)
{
  find();
  if (tab == 0)
    return -1;
  uint32 off = 0;
  while (off + 4 <= tab_len) {
    uint8 type = tab[off], flen = tab[off + 1];
    if (flen < 4)
      break;
    uint32 next = off + flen;
    while (next + 1 < tab_len && (tab[next] || tab[next + 1]))
      next++;
    next += 2;
    off = next > tab_len ? tab_len : next;
    if (type == 127)
      break;
  }
  *pa = tab_pa;
  *len = off;
  return 0;
}

// The first structure of `type`, and its length. Strings follow it.
static const uint8 *
find_struct(int type, uint8 *flen)
{
  uint32 off = 0;
  while (tab && off + 4 <= tab_len) {
    const uint8 *s = tab + off;
    if (s[1] < 4)
      return 0;
    if (s[0] == type) {
      *flen = s[1];
      return s;
    }
    if (s[0] == 127)
      return 0;
    uint32 next = off + s[1];
    while (next + 1 < tab_len && (tab[next] || tab[next + 1]))
      next++;
    off = next + 2;
  }
  return 0;
}

// String number `idx` of a structure, trimmed as Linux trims it.
static int
get_str(const uint8 *s, uint8 flen, int field, char *out, int cap)
{
  if (field >= flen)
    return -1;
  int idx = s[field];
  if (idx == 0)
    return -1;
  const char *p = (const char *)s + flen;
  const char *end = (const char *)tab + tab_len;
  while (--idx > 0 && p < end) {
    while (p < end && *p)
      p++;
    p++;
    if (p < end && *p == 0)          // the double NUL: there is no such string
      return -1;
  }
  int n = 0;
  while (p < end && *p == ' ')
    p++;
  while (p < end && *p && n < cap - 1)
    out[n++] = *p++;
  while (n > 0 && out[n - 1] == ' ')
    n--;
  out[n] = 0;
  return n ? n : -1;
}

static int
put_u(char *out, int cap, uint v)
{
  char t[12];
  int k = 0, n = 0;
  do { t[k++] = '0' + v % 10; v /= 10; } while (v);
  while (k && n < cap - 1)
    out[n++] = t[--k];
  out[n] = 0;
  return n;
}

int
dmi_field(int f, char *out, int cap)
{
  static const struct { uint8 type, off; } at[DMI_NFIELDS] = {
    [DMI_BIOS_VENDOR]     = { 0, 4 },  [DMI_BIOS_VERSION]    = { 0, 5 },
    [DMI_BIOS_DATE]       = { 0, 8 },
    [DMI_SYS_VENDOR]      = { 1, 4 },  [DMI_PRODUCT_NAME]    = { 1, 5 },
    [DMI_PRODUCT_VERSION] = { 1, 6 },  [DMI_PRODUCT_SKU]     = { 1, 0x19 },
    [DMI_PRODUCT_FAMILY]  = { 1, 0x1A },
    [DMI_BOARD_VENDOR]    = { 2, 4 },  [DMI_BOARD_NAME]      = { 2, 5 },
    [DMI_BOARD_VERSION]   = { 2, 6 },
    [DMI_CHASSIS_VENDOR]  = { 3, 4 },  [DMI_CHASSIS_VERSION] = { 3, 6 },
  };
  uint8 flen;
  const uint8 *s;

  if (f < 0 || f >= DMI_NFIELDS || cap < 2)
    return -1;
  find();
  if (tab == 0)
    return -1;

  if (f == DMI_BIOS_RELEASE) {
    if ((s = find_struct(0, &flen)) == 0 || flen < 0x16 ||
        s[0x14] == 0xFF || s[0x15] == 0xFF)
      return -1;
    int n = put_u(out, cap, s[0x14]);
    if (n < cap - 1) out[n++] = '.';
    return n + put_u(out + n, cap - n, s[0x15]);
  }
  if (f == DMI_CHASSIS_TYPE) {
    if ((s = find_struct(3, &flen)) == 0 || flen < 6)
      return -1;
    return put_u(out, cap, s[5] & 0x7F);
  }
  if ((s = find_struct(at[f].type, &flen)) == 0)
    return -1;
  return get_str(s, flen, at[f].off, out, cap);
}

// Linux's boot line, word for word in shape, because it is the line people
// search for: "DMI: LENOVO 20XW/20XW, BIOS N32ET75W (1.51 ) 09/05/2023".
void
dmi_init(void)
{
  char v[64], p[64], b[64], bv[64], bd[32];

  find();
  if (tab == 0) {
    cprintf("DMI: not present or invalid.\n");
    return;
  }
  if (dmi_field(DMI_SYS_VENDOR, v, sizeof v) < 0)       v[0] = 0;
  if (dmi_field(DMI_PRODUCT_NAME, p, sizeof p) < 0)     p[0] = 0;
  if (dmi_field(DMI_BOARD_NAME, b, sizeof b) < 0)       b[0] = 0;
  if (dmi_field(DMI_BIOS_VERSION, bv, sizeof bv) < 0)   bv[0] = 0;
  if (dmi_field(DMI_BIOS_DATE, bd, sizeof bd) < 0)      bd[0] = 0;
  cprintf("DMI: %s %s/%s, BIOS %s %s\n", v, p, b, bv, bd);
}