diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 17a6fa0..79d73e5 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -210,6 +210,247 @@ void acpi_table_print_madt_entry(struct acpi_subtable_header *header)
 	}
 }
 
+/*
+ * The Long, Sad, True Story of the MADT
+ *    or
+ * What does bad_madt_entry() actually do?
+ *
+ * Once upon a time in ACPI 1.0, there was the MADT.  It was a nice table,
+ * and it had two subtables all of its own.  But, it was also a pretty
+ * busy table, too, so over time the MADT gathered up other nice little
+ * subtables.  By the time ACPI 6.0 came around, the MADT had 16 of the
+ * little guys.
+ *
+ * Now, the MADT kept a little counter around for the subtables.  In fact,
+ * it kept two counters: one was the revision level, which was supposed to
+ * change when new subtables came to be, or as the ones already around grew
+ * up. The second counter was a type number, because the MADT needed a unique
+ * type for each subtable so he could tell them apart.  But, sometimes the
+ * MADT got so busy, he forgot to increment the revision level when he needed
+ * to.  Fortunately, the type counter kept increasing since that's the only
+ * way the MADT could find each little subtable.  It just wouldn't do to have
+ * every subtable called Number 6.
+ *
+ * In the next valley over, a castle full of wizards was watching the MADT
+ * and made a pact to keep their own counter.  Every time the MADT found a
+ * new subtable, or a subtable grew up, the wizards promised they would
+ * increment their counter.  Well, wizards being the forgetful sort, they
+ * didn't alway do that.  And, since there quite a lot of them, they
+ * couldn't always remember who was supposed to keep track of the MADT,
+ * especially if dinner was coming up soon.  Their counter was called the
+ * spec version.
+ *
+ * Every now and then, the MADT would gather up all its little subtables
+ * and take them in to the cobbler to get new boots.  This was a very, very
+ * meticulous cobbler, so every time they came, he wrote down all the boot
+ * sizes for all of the little subtables.  The cobbler would ask each subtable
+ * for its length, check that against his careful notes, and then go get the
+ * right boots.  Sometimes, a little subtable would change a bit, and their
+ * length did not match what the cobbler had written down.  If the wizards
+ * or the MADT had incremented their counters, the cobbler would breath a
+ * sigh of relief and write down the new length as the right one.  But, if
+ * none of the counters had changed, this would make the cobbler very, very
+ * mad.  He couldn't tell if he had the right size boots or not for the
+ * little subtable.  He would have to *guess* and this really bugged him.
+ *
+ * Well, when the cobbler got mad like this, he would go into hiding.  He
+ * would not make or sell any boots.  He would not go out at all.  Pretty
+ * soon, the coffee shop would have to close because the cobbler wasn't
+ * coming by twice a day any more.  Then the grocery store would have to
+ * close because he wouldn't eat much.  After a while, everyone would panic
+ * and have to move from the village and go live with all their relatives
+ * (usually the ones they didn't like very much).
+ *
+ * Eventually, the cobbler would work his way out of his bad mood, and
+ * open up his boot business again.  Then, everyone else could move back
+ * to the village and restart their lives, too.
+ *
+ * Fortunately, we have been able to collect up all the cobbler's careful
+ * notes (and we wrote them down below).  We'll have to keep checking these
+ * notes over time, too, just as the cobbler does.  But, in the meantime,
+ * we can avoid the panic and the reboot since we can make sure that each
+ * subtable is doing okay.  And that's what bad_madt_entry() does.
+ *
+ *
+ * FADT Major Version ->       1    3    4     4     5     5     6
+ * FADT Minor Version ->       x    x    x     x     x     1     0
+ * MADT revision ->            1    1    2     3     3     3     3
+ * Spec Version ->            1.0  2.0  3.0b  4.0a  5.0b  5.1a  6.0
+ * Subtable Name	Type  Expected Length ->
+ * Processor Local APIC  0x0    8    8    8     8     8     8     8
+ * IO APIC               0x1   12   12   12    12    12    12    12
+ * Int Src Override      0x2        10   10    10    10    10    10
+ * NMI Src               0x3         8    8     8     8     8     8
+ * Local APIC NMI Struct 0x4         6    6     6     6     6     6
+ * Local APIC Addr Ovrrd 0x5        16   12    12    12    12    12
+ * IO SAPIC              0x6        20   16    16    16    16    16
+ * Local SAPIC           0x7         8  >16   >16   >16   >16   >16
+ * Platform Int Src      0x8        16   16    16    16    16    16
+ * Proc Local x2APIC     0x9                   16    16    16    16
+ * Local x2APIC NMI      0xa                   12    12    12    12
+ * GICC CPU I/F          0xb                         40    76    80
+ * GICD                  0xc                         24    24    24
+ * GICv2m MSI            0xd                               24    24
+ * GICR                  0xe                               16    16
+ * GIC ITS               0xf                                     16
+ *
+ * In the table, each length entry is what should be in the length
+ * field of the subtable, and -- in general -- it should match the
+ * size of the struct for the subtable.  Any value that is not set
+ * (i.e., is zero) indicates that the subtable is not defined for
+ * that version of the ACPI spec.
+ *
+ */
+#define SUBTABLE_UNDEFINED	0x00
+#define SUBTABLE_VARIABLE	0xff
+#define NUM_SUBTABLE_TYPES	16
+
+struct acpi_madt_subtable_lengths {
+	unsigned short major_version;	/* from revision in FADT header */
+	unsigned short minor_version;	/* FADT field starting with 5.1 */
+	unsigned short madt_version;	/* MADT revision */
+	unsigned short num_types;	/* types possible for this version */
+	unsigned short lengths[NUM_SUBTABLE_TYPES];
+					/* subtable lengths, indexed by type */
+};
+
+static struct acpi_madt_subtable_lengths spec_info[] = {
+	{ /* for ACPI 1.0 */
+		.major_version = 1,
+		.minor_version = 0,
+		.madt_version = 1,
+		.num_types = 2,
+		.lengths = { 8, 12 }
+	},
+	{ /* for ACPI 2.0 */
+		.major_version = 3,
+		.minor_version = 0,
+		.madt_version = 1,
+		.num_types = 9,
+		.lengths = { 8, 12, 10, 8, 6, 16, 20, 8, 16 }
+	},
+	{ /* for ACPI 3.0b */
+		.major_version = 4,
+		.minor_version = 0,
+		.madt_version = 2,
+		.num_types = 9,
+		.lengths = { 8, 12, 10, 8, 6, 12, 16, SUBTABLE_VARIABLE, 16 }
+	},
+	{ /* for ACPI 4.0a */
+		.major_version = 4,
+		.minor_version = 0,
+		.madt_version = 3,
+		.num_types = 11,
+		.lengths = { 8, 12, 10, 8, 6, 12, 16, SUBTABLE_VARIABLE,
+			     16, 16, 12 }
+	},
+	{ /* for ACPI 5.0b */
+		.major_version = 5,
+		.minor_version = 0,
+		.madt_version = 3,
+		.num_types = 13,
+		.lengths = { 8, 12, 10, 8, 6, 12, 16, SUBTABLE_VARIABLE,
+			     16, 16, 12, 40, 24 }
+	},
+	{ /* for ACPI 5.1a */
+		.major_version = 5,
+		.minor_version = 1,
+		.madt_version = 3,
+		.num_types = 15,
+		.lengths = { 8, 12, 10, 8, 6, 12, 16, SUBTABLE_VARIABLE,
+			     16, 16, 12, 76, 24, 24, 16 }
+	},
+	{ /* for ACPI 6.0 */
+		.major_version = 6,
+		.minor_version = 0,
+		.madt_version = 3,
+		.num_types = 16,
+		.lengths = { 8, 12, 10, 8, 6, 12, 16, SUBTABLE_VARIABLE,
+			     16, 16, 12, 80, 24, 24, 16, 16 }
+	},
+	{ /* terminator */
+		.major_version = 0,
+		.minor_version = 0,
+		.madt_version = 0,
+		.num_types = 0,
+		.lengths = { 0 }
+	}
+};
+
+static int __init bad_madt_entry(struct acpi_table_header *table,
+				 struct acpi_subtable_header *entry)
+{
+	struct acpi_madt_subtable_lengths *ms;
+	struct acpi_table_madt *madt;
+	unsigned short major;
+	unsigned short minor;
+	unsigned short len;
+
+	/* simple sanity checking on MADT subtable entries */
+	if (!entry || !table)
+		return 1;
+
+	/* FADT minor numbers were not introduced until ACPI 5.1 */
+	major = acpi_gbl_FADT.header.revision;
+	if (major >= 5 && acpi_gbl_FADT.header.length >= 268)
+		minor = acpi_gbl_FADT.minor_revision;
+	else
+		minor = 0;
+
+	madt = (struct acpi_table_madt *)table;
+	ms = spec_info;
+	while (ms->num_types != 0) {
+		if (ms->major_version == major &&
+		    ms->minor_version == minor &&
+		    ms->madt_version == madt->header.revision)
+			break;
+		ms++;
+	}
+	if (!ms->num_types) {
+		pr_err("undefined version for either FADT %d.%d or MADT %d\n",
+		       major, minor, madt->header.revision);
+		return 1;
+	}
+
+	if (entry->type >= ms->num_types) {
+		pr_err("undefined MADT subtable type for FADT %d.%d: %d (length %d)\n",
+		       major, minor, entry->type, entry->length);
+		return 1;
+	}
+
+	/* verify that the table is allowed for this version of the spec */
+	len = ms->lengths[entry->type];
+	if (!len) {
+		pr_err("MADT subtable %d not defined for FADT %d.%d\n",
+			 entry->type, major, minor);
+		return 1;
+	}
+
+	/* verify that the length is what we expect */
+	if (len == SUBTABLE_VARIABLE) {
+		if (entry->type == ACPI_MADT_TYPE_LOCAL_SAPIC) {
+			struct acpi_madt_local_sapic *lsapic =
+				(struct acpi_madt_local_sapic *)entry;
+			int proper_len = sizeof(struct acpi_madt_local_sapic) +
+					 strlen(lsapic->uid_string) + 1;
+
+			if (proper_len != entry->length) {
+				pr_err("Variable length MADT subtable %d is wrong length: %d, should be: %d\n",
+				       entry->type, entry->length, proper_len);
+				return 1;
+			}
+		}
+	} else {
+		if (entry->length != len) {
+			pr_err("MADT subtable %d is wrong length: %d, should be: %d\n",
+			       entry->type, entry->length, len);
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
 int __init
 acpi_parse_entries(char *id, unsigned long table_size,
 		acpi_tbl_entry_handler handler,
@@ -245,6 +486,9 @@ acpi_parse_entries(char *id, unsigned long table_size,
 	       table_end) {
 		if (entry->type == entry_id
 		    && (!max_entries || count < max_entries)) {
+			if (!strncmp(id, ACPI_SIG_MADT, 4) &&
+			    bad_madt_entry(table_header, entry))
+				return -EINVAL;
 			if (handler(entry, table_end))
 				return -EINVAL;
 
