[PATCH v2] acpi: acpica: fix acpi operand cache leak

[Seunghun Han]

I'm Seunghun Han, and I work for National Security Research Institute of
South Korea.

I have been doing a research on ACPI and making a handcrafted ACPI table
for my research.
Errors of handcrafted ACPI tables are handled well in Linux kernel while boot
process, and Linux kernel goes well without critical problems.
But I found some ACPI operand cache leaks in ACPI early abort cases.

Boot log of ACPI operand cache leak is as follows:
>[    0.174332] ACPI: Added _OSI(Module Device)
>[    0.175504] ACPI: Added _OSI(Processor Device)
>[    0.176010] ACPI: Added _OSI(3.0 _SCP Extensions)
>[    0.177032] ACPI: Added _OSI(Processor Aggregator Device)
>[    0.178284] ACPI: SCI (IRQ16705) allocation failed
>[    0.179352] ACPI Exception: AE_NOT_ACQUIRED, Unable to install System Control Interrupt handler (20160930/evevent-131)
>[    0.180008] ACPI: Unable to start the ACPI Interpreter
>[    0.181125] ACPI Error: Could not remove SCI handler (20160930/evmisc-281)
>[    0.184068] kmem_cache_destroy Acpi-Operand: Slab cache still has objects
>[    0.185358] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.10.0-rc3 #2
>[    0.186820] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>[    0.188000] Call Trace:
>[    0.188000]  ? dump_stack+0x5c/0x7d
>[    0.188000]  ? kmem_cache_destroy+0x224/0x230
>[    0.188000]  ? acpi_sleep_proc_init+0x22/0x22
>[    0.188000]  ? acpi_os_delete_cache+0xa/0xd
>[    0.188000]  ? acpi_ut_delete_caches+0x3f/0x7b
>[    0.188000]  ? acpi_terminate+0x5/0xf
>[    0.188000]  ? acpi_init+0x288/0x32e
>[    0.188000]  ? __class_create+0x4c/0x80
>[    0.188000]  ? video_setup+0x7a/0x7a
>[    0.188000]  ? do_one_initcall+0x4e/0x1b0
>[    0.188000]  ? kernel_init_freeable+0x194/0x21a
>[    0.188000]  ? rest_init+0x80/0x80
>[    0.188000]  ? kernel_init+0xa/0x100
>[    0.188000]  ? ret_from_fork+0x25/0x30

When early abort is occurred due to invalid ACPI information, Linux kernel
terminates ACPI by calling acpi_terminate() function.
The function calls acpi_ns_terminate() function to delete namespace data
and ACPI operand cache (acpi_gbl_module_code_list).

But the deletion code in acpi_ns_terminate() function is wrapped in
ACPI_EXEC_APP definition, therefore the code is only executed when the
definition exists.
If the define doesn't exist, ACPI operand cache (acpi_gbl_module_code_list) is
leaked, and stack dump is shown in kernel log.

This causes a security threat because the old kernel (<= 4.9) shows memory
locations of kernel functions in stack dump, therefore kernel ASLR can be
neutralized.

To fix ACPI operand leak for enhancing security, I made a patch which removes
the ACPI_EXEC_APP define in acpi_ns_terminate() function for executing the
deletion code unconditionally.

I hope that this patch improves the security of Linux kernel.

Thank you.

Signed-off-by: Seunghun Han <kkamagui@xxxxxxxxx>
---
Changes since v1: move position of variables to remove compile warning.

drivers/acpi/acpica/nsutils.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/acpi/acpica/nsutils.c b/drivers/acpi/acpica/nsutils.c
index 691814d..943702d 100644
--- a/drivers/acpi/acpica/nsutils.c
+++ b/drivers/acpi/acpica/nsutils.c
@@ -594,25 +594,20 @@ struct acpi_namespace_node *acpi_ns_validate_handle(acpi_handle handle)
 void acpi_ns_terminate(void)
 {
 	acpi_status status;
+	union acpi_operand_object *prev;
+	union acpi_operand_object *next;
 
 	ACPI_FUNCTION_TRACE(ns_terminate);
 
-#ifdef ACPI_EXEC_APP
-	{
-		union acpi_operand_object *prev;
-		union acpi_operand_object *next;
+	/* Delete any module-level code blocks */
 
-		/* Delete any module-level code blocks */
-
-		next = acpi_gbl_module_code_list;
-		while (next) {
-			prev = next;
-			next = next->method.mutex;
-			prev->method.mutex = NULL;	/* Clear the Mutex (cheated) field */
-			acpi_ut_remove_reference(prev);
-		}
+	next = acpi_gbl_module_code_list;
+	while (next) {
+		prev = next;
+		next = next->method.mutex;
+		prev->method.mutex = NULL;	/* Clear the Mutex (cheated) field */
+		acpi_ut_remove_reference(prev);
 	}
-#endif
 
 	/*
 	 * Free the entire namespace -- all nodes and all objects
-- 
2.1.4