diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index a3d012b..180ac43 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -1,22 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  acpi_tables.c - ACPI Boot-Time Table Parsing
  *
  *  Copyright (C) 2001 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
- *
- * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- *
- *  This program is free software; you can redistribute it and/or modify
- *  it under the terms of the GNU General Public License as published by
- *  the Free Software Foundation; either version 2 of the License, or
- *  (at your option) any later version.
- *
- *  This program is distributed in the hope that it will be useful,
- *  but WITHOUT ANY WARRANTY; without even the implied warranty of
- *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *  GNU General Public License for more details.
- *
- * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- *
  */
 
 /* Uncomment next line to get verbose printout */
@@ -31,10 +17,10 @@
 #include <linux/irq.h>
 #include <linux/errno.h>
 #include <linux/acpi.h>
-#include <linux/bootmem.h>
-#include <linux/earlycpio.h>
 #include <linux/memblock.h>
+#include <linux/earlycpio.h>
 #include <linux/initrd.h>
+#include <linux/security.h>
 #include "internal.h"
 
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
@@ -50,6 +36,16 @@
 
 static int acpi_apic_instance __initdata;
 
+enum acpi_subtable_type {
+	ACPI_SUBTABLE_COMMON,
+	ACPI_SUBTABLE_HMAT,
+};
+
+struct acpi_subtable_entry {
+	union acpi_subtable_headers *hdr;
+	enum acpi_subtable_type type;
+};
+
 /*
  * Disable table checksum verification for the early stage due to the size
  * limitation of the current x86 early mapping implementation.
@@ -218,6 +214,50 @@
 	}
 }
 
+static unsigned long __init
+acpi_get_entry_type(struct acpi_subtable_entry *entry)
+{
+	switch (entry->type) {
+	case ACPI_SUBTABLE_COMMON:
+		return entry->hdr->common.type;
+	case ACPI_SUBTABLE_HMAT:
+		return entry->hdr->hmat.type;
+	}
+	return 0;
+}
+
+static unsigned long __init
+acpi_get_entry_length(struct acpi_subtable_entry *entry)
+{
+	switch (entry->type) {
+	case ACPI_SUBTABLE_COMMON:
+		return entry->hdr->common.length;
+	case ACPI_SUBTABLE_HMAT:
+		return entry->hdr->hmat.length;
+	}
+	return 0;
+}
+
+static unsigned long __init
+acpi_get_subtable_header_length(struct acpi_subtable_entry *entry)
+{
+	switch (entry->type) {
+	case ACPI_SUBTABLE_COMMON:
+		return sizeof(entry->hdr->common);
+	case ACPI_SUBTABLE_HMAT:
+		return sizeof(entry->hdr->hmat);
+	}
+	return 0;
+}
+
+static enum acpi_subtable_type __init
+acpi_get_subtable_type(char *id)
+{
+	if (strncmp(id, ACPI_SIG_HMAT, 4) == 0)
+		return ACPI_SUBTABLE_HMAT;
+	return ACPI_SUBTABLE_COMMON;
+}
+
 /**
  * acpi_parse_entries_array - for each proc_num find a suitable subtable
  *
@@ -241,14 +281,13 @@
  * On success returns sum of all matching entries for all proc handlers.
  * Otherwise, -ENODEV or -EINVAL is returned.
  */
-static int __init
-acpi_parse_entries_array(char *id, unsigned long table_size,
+static int __init acpi_parse_entries_array(char *id, unsigned long table_size,
 		struct acpi_table_header *table_header,
 		struct acpi_subtable_proc *proc, int proc_num,
 		unsigned int max_entries)
 {
-	struct acpi_subtable_header *entry;
-	unsigned long table_end;
+	struct acpi_subtable_entry entry;
+	unsigned long table_end, subtable_len, entry_len;
 	int count = 0;
 	int errs = 0;
 	int i;
@@ -271,19 +310,20 @@
 
 	/* Parse all entries looking for a match. */
 
-	entry = (struct acpi_subtable_header *)
+	entry.type = acpi_get_subtable_type(id);
+	entry.hdr = (union acpi_subtable_headers *)
 	    ((unsigned long)table_header + table_size);
+	subtable_len = acpi_get_subtable_header_length(&entry);
 
-	while (((unsigned long)entry) + sizeof(struct acpi_subtable_header) <
-	       table_end) {
+	while (((unsigned long)entry.hdr) + subtable_len  < table_end) {
 		if (max_entries && count >= max_entries)
 			break;
 
 		for (i = 0; i < proc_num; i++) {
-			if (entry->type != proc[i].id)
+			if (acpi_get_entry_type(&entry) != proc[i].id)
 				continue;
 			if (!proc[i].handler ||
-			     (!errs && proc[i].handler(entry, table_end))) {
+			     (!errs && proc[i].handler(entry.hdr, table_end))) {
 				errs++;
 				continue;
 			}
@@ -298,13 +338,14 @@
 		 * If entry->length is 0, break from this loop to avoid
 		 * infinite loop.
 		 */
-		if (entry->length == 0) {
+		entry_len = acpi_get_entry_length(&entry);
+		if (entry_len == 0) {
 			pr_err("[%4.4s:0x%02x] Invalid zero length\n", id, proc->id);
 			return -EINVAL;
 		}
 
-		entry = (struct acpi_subtable_header *)
-		    ((unsigned long)entry + entry->length);
+		entry.hdr = (union acpi_subtable_headers *)
+		    ((unsigned long)entry.hdr + entry_len);
 	}
 
 	if (max_entries && count > max_entries) {
@@ -315,8 +356,7 @@
 	return errs ? -EINVAL : count;
 }
 
-int __init
-acpi_table_parse_entries_array(char *id,
+int __init acpi_table_parse_entries_array(char *id,
 			 unsigned long table_size,
 			 struct acpi_subtable_proc *proc, int proc_num,
 			 unsigned int max_entries)
@@ -347,8 +387,7 @@
 	return count;
 }
 
-int __init
-acpi_table_parse_entries(char *id,
+int __init acpi_table_parse_entries(char *id,
 			unsigned long table_size,
 			int entry_id,
 			acpi_tbl_entry_handler handler,
@@ -363,8 +402,7 @@
 						max_entries);
 }
 
-int __init
-acpi_table_parse_madt(enum acpi_madt_type id,
+int __init acpi_table_parse_madt(enum acpi_madt_type id,
 		      acpi_tbl_entry_handler handler, unsigned int max_entries)
 {
 	return acpi_table_parse_entries(ACPI_SIG_MADT,
@@ -453,16 +491,17 @@
 
 /* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
 static const char * const table_sigs[] = {
-	ACPI_SIG_BERT, ACPI_SIG_CPEP, ACPI_SIG_ECDT, ACPI_SIG_EINJ,
-	ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT, ACPI_SIG_MSCT,
-	ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT, ACPI_SIG_ASF,
-	ACPI_SIG_BOOT, ACPI_SIG_DBGP, ACPI_SIG_DMAR, ACPI_SIG_HPET,
-	ACPI_SIG_IBFT, ACPI_SIG_IVRS, ACPI_SIG_MCFG, ACPI_SIG_MCHI,
-	ACPI_SIG_SLIC, ACPI_SIG_SPCR, ACPI_SIG_SPMI, ACPI_SIG_TCPA,
-	ACPI_SIG_UEFI, ACPI_SIG_WAET, ACPI_SIG_WDAT, ACPI_SIG_WDDT,
-	ACPI_SIG_WDRT, ACPI_SIG_DSDT, ACPI_SIG_FADT, ACPI_SIG_PSDT,
-	ACPI_SIG_RSDT, ACPI_SIG_XSDT, ACPI_SIG_SSDT, ACPI_SIG_IORT,
-	ACPI_SIG_NFIT, ACPI_SIG_HMAT, ACPI_SIG_PPTT, NULL };
+	ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
+	ACPI_SIG_EINJ, ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT,
+	ACPI_SIG_MSCT, ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT,
+	ACPI_SIG_ASF,  ACPI_SIG_BOOT, ACPI_SIG_DBGP, ACPI_SIG_DMAR,
+	ACPI_SIG_HPET, ACPI_SIG_IBFT, ACPI_SIG_IVRS, ACPI_SIG_MCFG,
+	ACPI_SIG_MCHI, ACPI_SIG_SLIC, ACPI_SIG_SPCR, ACPI_SIG_SPMI,
+	ACPI_SIG_TCPA, ACPI_SIG_UEFI, ACPI_SIG_WAET, ACPI_SIG_WDAT,
+	ACPI_SIG_WDDT, ACPI_SIG_WDRT, ACPI_SIG_DSDT, ACPI_SIG_FADT,
+	ACPI_SIG_PSDT, ACPI_SIG_RSDT, ACPI_SIG_XSDT, ACPI_SIG_SSDT,
+	ACPI_SIG_IORT, ACPI_SIG_NFIT, ACPI_SIG_HMAT, ACPI_SIG_PPTT,
+	NULL };
 
 #define ACPI_HEADER_SIZE sizeof(struct acpi_table_header)
 
@@ -474,14 +513,22 @@
 
 void __init acpi_table_upgrade(void)
 {
-	void *data = (void *)initrd_start;
-	size_t size = initrd_end - initrd_start;
+	void *data;
+	size_t size;
 	int sig, no, table_nr = 0, total_offset = 0;
 	long offset = 0;
 	struct acpi_table_header *table;
 	char cpio_path[32] = "kernel/firmware/acpi/";
 	struct cpio_data file;
 
+	if (IS_ENABLED(CONFIG_ACPI_TABLE_OVERRIDE_VIA_BUILTIN_INITRD)) {
+		data = __initramfs_start;
+		size = __initramfs_size;
+	} else {
+		data = (void *)initrd_start;
+		size = initrd_end - initrd_start;
+	}
+
 	if (data == NULL || size == 0)
 		return;
 
@@ -532,6 +579,11 @@
 	if (table_nr == 0)
 		return;
 
+	if (security_locked_down(LOCKDOWN_ACPI_TABLES)) {
+		pr_notice("kernel is locked down, ignoring table override\n");
+		return;
+	}
+
 	acpi_tables_addr =
 		memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS,
 				       all_tables_size, PAGE_SIZE);
@@ -663,8 +715,8 @@
 		table_length = table->length;
 
 		/* Skip RSDT/XSDT which should only be used for override */
-		if (ACPI_COMPARE_NAME(table->signature, ACPI_SIG_RSDT) ||
-		    ACPI_COMPARE_NAME(table->signature, ACPI_SIG_XSDT)) {
+		if (ACPI_COMPARE_NAMESEG(table->signature, ACPI_SIG_RSDT) ||
+		    ACPI_COMPARE_NAMESEG(table->signature, ACPI_SIG_XSDT)) {
 			acpi_os_unmap_memory(table, ACPI_HEADER_SIZE);
 			goto next_table;
 		}
@@ -713,8 +765,12 @@
 					  table_length);
 }
 
-acpi_status
-acpi_os_table_override(struct acpi_table_header *existing_table,
+#ifdef CONFIG_ACPI_CUSTOM_DSDT
+static void *amlcode __attribute__ ((weakref("AmlCode")));
+static void *dsdt_amlcode __attribute__ ((weakref("dsdt_aml_code")));
+#endif
+
+acpi_status acpi_os_table_override(struct acpi_table_header *existing_table,
 		       struct acpi_table_header **new_table)
 {
 	if (!existing_table || !new_table)
@@ -723,8 +779,11 @@
 	*new_table = NULL;
 
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
-	if (strncmp(existing_table->signature, "DSDT", 4) == 0)
-		*new_table = (struct acpi_table_header *)AmlCode;
+	if (!strncmp(existing_table->signature, "DSDT", 4)) {
+		*new_table = (struct acpi_table_header *)&amlcode;
+		if (!(*new_table))
+			*new_table = (struct acpi_table_header *)&dsdt_amlcode;
+	}
 #endif
 	if (*new_table != NULL)
 		acpi_table_taint(existing_table);
@@ -773,7 +832,6 @@
 
 	return 0;
 }
-
 early_param("acpi_apic_instance", acpi_parse_apic_instance);
 
 static int __init acpi_force_table_verification_setup(char *s)
@@ -782,7 +840,6 @@
 
 	return 0;
 }
-
 early_param("acpi_force_table_verification", acpi_force_table_verification_setup);
 
 static int __init acpi_force_32bit_fadt_addr(char *s)
@@ -792,5 +849,4 @@
 
 	return 0;
 }
-
 early_param("acpi_force_32bit_fadt_addr", acpi_force_32bit_fadt_addr);