Commit 4f90742d authored by Francesco Pompo's avatar Francesco Pompo Committed by Ard Biesheuvel
Browse files

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: default avatarFrancesco Pompo <francescopompo2@gmail.com>
[ardb: cosmetic tweaks]
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
parent 3a866087

drivers/firmware/efi/libstub/x86-stub.c

+100 −1
Original line number Diff line number Diff line
@@ -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;