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Message-ID: <20251102001411.108385-1-francescopompo2@gmail.com>
Date: Sun, 2 Nov 2025 01:13:11 +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] efistub/smbios: Add fallback for SMBIOS record lookup
Some UEFI firmware implementations 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. Log when the fallback is used.
Signed-off-by: Francesco Pompo <francescopompo2@...il.com>
---
drivers/firmware/efi/libstub/efistub.h | 17 +++++
drivers/firmware/efi/libstub/smbios.c | 99 +++++++++++++++++++++++++-
2 files changed, 113 insertions(+), 3 deletions(-)
diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index 685098f9626f..68582ce81370 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -1151,6 +1151,23 @@ void free_screen_info(struct screen_info *si);
void efi_cache_sync_image(unsigned long image_base,
unsigned long alloc_size);
+struct __packed 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;
+};
+
struct efi_smbios_record {
u8 type;
u8 length;
diff --git a/drivers/firmware/efi/libstub/smbios.c b/drivers/firmware/efi/libstub/smbios.c
index f31410d7e7e1..21f499035b37 100644
--- a/drivers/firmware/efi/libstub/smbios.c
+++ b/drivers/firmware/efi/libstub/smbios.c
@@ -33,6 +33,93 @@ union efi_smbios_protocol {
} mixed_mode;
};
+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);
+}
+
const struct efi_smbios_record *efi_get_smbios_record(u8 type)
{
struct efi_smbios_record *record;
@@ -43,9 +130,15 @@ const struct efi_smbios_record *efi_get_smbios_record(u8 type)
status = efi_bs_call(locate_protocol, &EFI_SMBIOS_PROTOCOL_GUID, NULL,
(void **)&smbios) ?:
efi_call_proto(smbios, get_next, &handle, &type, &record, NULL);
- if (status != EFI_SUCCESS)
- return NULL;
- return record;
+ if (status == EFI_SUCCESS)
+ return record;
+
+ efi_info(
+ "Cannot access SMBIOS protocol (status 0x%lx), parsing table directly\n",
+ status
+ );
+
+ return get_table_record(type);
}
const u8 *__efi_get_smbios_string(const struct efi_smbios_record *record,
--
2.51.0
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