ACPI: PPTT: Fix processor subtable walk

The original PPTT code had a bug where the processor subtable length
was not correctly validated when encountering a truncated
acpi_pptt_processor node.

Commit 7ab4f0e ("ACPI PPTT: Fix coding mistakes in a couple of
sizeof() calls") attempted to fix this by validating the size is as
large as the acpi_pptt_processor node structure. This introduced a
regression where the last processor node in the PPTT table is ignored
if it doesn't contain any private resources. That results errors like:

  ACPI PPTT: PPTT table found, but unable to locate core XX (XX)
  ACPI: SPE must be homogeneous

Furthermore, it fails in a common case where the node length isn't
equal to the acpi_pptt_processor structure size, leaving the original
bug in a modified form.

Correct the regression by adjusting the loop termination conditions as
suggested by the bug reporters. An additional check performed after
the subtable node type is detected, validates the acpi_pptt_processor
node is fully contained in the PPTT table. Repeating the check in
acpi_pptt_leaf_node() is largely redundant as the node is already
known to be fully contained in the table.

The case where a final truncated node's parent property is accepted,
but the node itself is rejected should not be considered a bug.

Fixes: 7ab4f0e ("ACPI PPTT: Fix coding mistakes in a couple of sizeof() calls")
Reported-by: Maximilian Heyne <mheyne@amazon.de>
Closes: https://lore.kernel.org/linux-acpi/20250506-draco-taped-15f475cd@mheyne-amazon/
Reported-by: Yicong Yang <yangyicong@hisilicon.com>
Closes: https://lore.kernel.org/linux-acpi/20250507035124.28071-1-yangyicong@huawei.com/
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Tested-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Maximilian Heyne <mheyne@amazon.de>
Cc: All applicable <stable@vger.kernel.org> # 7ab4f0e: ACPI PPTT: Fix coding mistakes ...
Link: https://patch.msgid.link/20250508023025.1301030-1-jeremy.linton@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: jlintonarm

drivers/acpi/pptt.c

@@ -231,16 +231,18 @@ static int acpi_pptt_leaf_node(struct acpi_table_header *table_hdr,
 			     sizeof(struct acpi_table_pptt));
 	proc_sz = sizeof(struct acpi_pptt_processor);
 
-	while ((unsigned long)entry + proc_sz < table_end) {
+	/* ignore subtable types that are smaller than a processor node */
+	while ((unsigned long)entry + proc_sz <= table_end) {
 		cpu_node = (struct acpi_pptt_processor *)entry;
+
 		if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
 		    cpu_node->parent == node_entry)
 			return 0;
 		if (entry->length == 0)
 			return 0;
+
 		entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
 				     entry->length);
-
 	}
 	return 1;
 }
@@ -273,15 +275,18 @@ static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_he
 	proc_sz = sizeof(struct acpi_pptt_processor);
 
 	/* find the processor structure associated with this cpuid */
-	while ((unsigned long)entry + proc_sz < table_end) {
+	while ((unsigned long)entry + proc_sz <= table_end) {
 		cpu_node = (struct acpi_pptt_processor *)entry;
 
 		if (entry->length == 0) {
 			pr_warn("Invalid zero length subtable\n");
 			break;
 		}
+		/* entry->length may not equal proc_sz, revalidate the processor structure length */
 		if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
 		    acpi_cpu_id == cpu_node->acpi_processor_id &&
+		    (unsigned long)entry + entry->length <= table_end &&
+		    entry->length == proc_sz + cpu_node->number_of_priv_resources * sizeof(u32) &&
 		     acpi_pptt_leaf_node(table_hdr, cpu_node)) {
 			return (struct acpi_pptt_processor *)entry;
 		}