efistub/x86: Add fallback for SMBIOS record lookup

Some Apple EFI firmwares do not provide the SMBIOS Protocol,
causing efi_get_smbios_record() to fail. This prevents retrieval of
system information such as product name, which is needed by
apple_set_os() to enable the integrated GPU on dual-graphics Intel
MacBooks.

Add a fallback that directly parses the SMBIOS entry point table when
the protocol is unavailable.

Signed-off-by: Francesco Pompo <francescopompo2@gmail.com>
[ardb: cosmetic tweaks]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 761121a77f9e4b6fa26f4fe6fcca16a16a55f4e7..dd9e19c31dd7c5e8a069228882187e9ee6c4493c 100644 (file)
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -203,6 +203,104 @@ static void retrieve_apple_device_properties(struct boot_params *boot_params)
        }
 }
 
+struct smbios_entry_point {
+       u8      anchor[4];
+       u8      ep_checksum;
+       u8      ep_length;
+       u8      major_version;
+       u8      minor_version;
+       u16     max_size_entry;
+       u8      ep_rev;
+       u8      reserved[5];
+
+       struct __packed {
+               u8      anchor[5];
+               u8      checksum;
+               u16     st_length;
+               u32     st_address;
+               u16     number_of_entries;
+               u8      bcd_rev;
+       } intm;
+};
+
+static bool verify_ep_checksum(const void *ptr, int length)
+{
+       u8 sum = 0;
+
+       for (int i = 0; i < length; i++)
+               sum += ((u8 *)ptr)[i];
+
+       return sum == 0;
+}
+
+static bool verify_ep_integrity(const struct smbios_entry_point *ep)
+{
+       if (memcmp(ep->anchor, "_SM_", sizeof(ep->anchor)) != 0)
+               return false;
+
+       if (memcmp(ep->intm.anchor, "_DMI_", sizeof(ep->intm.anchor)) != 0)
+               return false;
+
+       if (!verify_ep_checksum(ep, ep->ep_length) ||
+           !verify_ep_checksum(&ep->intm, sizeof(ep->intm)))
+               return false;
+
+       return true;
+}
+
+static const struct efi_smbios_record *search_record(void *table, u32 length,
+                                                    u8 type)
+{
+       const u8 *p, *end;
+
+       p = (u8 *)table;
+       end = p + length;
+
+       while (p + sizeof(struct efi_smbios_record) < end) {
+               const struct efi_smbios_record *hdr =
+                       (struct efi_smbios_record *)p;
+               const u8 *next;
+
+               if (hdr->type == type)
+                       return hdr;
+
+               /* Type 127 = End-of-Table */
+               if (hdr->type == 0x7F)
+                       return NULL;
+
+               /* Jumping to the unformed section */
+               next = p + hdr->length;
+
+               /* Unformed section ends with 0000h */
+               while ((next[0] != 0 || next[1] != 0) && next + 1 < end)
+                       next++;
+
+               next += 2;
+               p = next;
+       }
+
+       return NULL;
+}
+
+static const struct efi_smbios_record *get_table_record(u8 type)
+{
+       const struct smbios_entry_point *ep;
+
+       /*
+        * Locate the legacy 32-bit SMBIOS entrypoint in memory, and parse it
+        * directly. Needed by some Macs that do not implement the EFI protocol.
+        */
+       ep = get_efi_config_table(SMBIOS_TABLE_GUID);
+       if (!ep)
+               return NULL;
+
+       if (!verify_ep_integrity(ep))
+               return NULL;
+
+       return search_record((void *)(unsigned long)ep->intm.st_address,
+                            ep->intm.st_length, type);
+}
+
 static bool apple_match_product_name(void)
 {
        static const char type1_product_matches[][15] = {
@@ -218,7 +316,8 @@ static bool apple_match_product_name(void)
        const struct efi_smbios_type1_record *record;
        const u8 *product;
 
-       record = (struct efi_smbios_type1_record *)efi_get_smbios_record(1);
+       record = (struct efi_smbios_type1_record *)
+                       (efi_get_smbios_record(1) ?: get_table_record(1));
        if (!record)
                return false;