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Message-ID: <20251103123335.1089483-1-francescopompo2@gmail.com>
Date: Mon, 3 Nov 2025 13:25:39 +0100
From: Francesco Pompo <francescopompo2@...il.com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: linux-efi@...r.kernel.org,
linux-kernel@...r.kernel.org,
Francesco Pompo <francescopompo2@...il.com>
Subject: [PATCH v2] 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@...il.com>
---
drivers/firmware/efi/libstub/x86-stub.c | 107 +++++++++++++++++++++++-
1 file changed, 106 insertions(+), 1 deletion(-)
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index f8e465da344d..13059412fdb9 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -225,6 +225,110 @@ static void retrieve_apple_device_properties(struct boot_params *boot_params)
}
}
+struct smbios_entry_point {
+ char anchor[4];
+ u8 ep_checksum;
+ u8 ep_length;
+ u8 major_version;
+ u8 minor_version;
+ u16 max_size_entry;
+ u8 ep_rev;
+ u8 reserved[5];
+ char int_anchor[5];
+ u8 int_checksum;
+ u16 st_length;
+ u32 st_address;
+ u16 number_of_entries;
+ u8 bcd_rev;
+};
+
+static bool verify_ep_checksum(const struct smbios_entry_point *ep)
+{
+ const u8 *ptr = (u8 *)ep;
+ u8 sum = 0;
+ int i;
+
+ for (i = 0; i < ep->ep_length; i++)
+ sum += ptr[i];
+
+ return sum == 0;
+}
+
+static bool verify_ep_int_checksum(const struct smbios_entry_point *ep)
+{
+ const u8 *ptr = (u8 *)&ep->int_anchor;
+ u8 sum = 0;
+ int i;
+
+ for (i = 0; i < 15; i++)
+ sum += 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->int_anchor, "_DMI_", sizeof(ep->int_anchor)) != 0)
+ return false;
+
+ if (!verify_ep_checksum(ep) || !verify_ep_int_checksum(ep))
+ 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;
+
+ 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->st_address,
+ ep->st_length, type);
+}
+
static bool apple_match_product_name(void)
{
static const char type1_product_matches[][15] = {
@@ -240,7 +344,8 @@ 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;
--
2.50.1
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