[PATCH V4] acpi: acpica: fix acpi parse and parseext cache leaks

[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 found an ACPI cache leak in ACPI
early abort cases.

Boot log of ACPI cache leak is as follows:
[    0.352414] ACPI: Added _OSI(Module Device)
[    0.353182] ACPI: Added _OSI(Processor Device)
[    0.353182] ACPI: Added _OSI(3.0 _SCP Extensions)
[    0.353182] ACPI: Added _OSI(Processor Aggregator Device)
[    0.356028] ACPI: Unable to start the ACPI Interpreter
[    0.356799] ACPI Error: Could not remove SCI handler (20170303/evmisc-281)
[    0.360215] kmem_cache_destroy Acpi-State: Slab cache still has objects
[    0.360648] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G        W
4.12.0-rc4-next-20170608+ #10
[    0.361273] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS
VirtualBox 12/01/2006
[    0.361873] Call Trace:
[    0.362243]  ? dump_stack+0x5c/0x81
[    0.362591]  ? kmem_cache_destroy+0x1aa/0x1c0
[    0.362944]  ? acpi_sleep_proc_init+0x27/0x27
[    0.363296]  ? acpi_os_delete_cache+0xa/0x10
[    0.363646]  ? acpi_ut_delete_caches+0x6d/0x7b
[    0.364000]  ? acpi_terminate+0xa/0x14
[    0.364000]  ? acpi_init+0x2af/0x34f
[    0.364000]  ? __class_create+0x4c/0x80
[    0.364000]  ? video_setup+0x7f/0x7f
[    0.364000]  ? acpi_sleep_proc_init+0x27/0x27
[    0.364000]  ? do_one_initcall+0x4e/0x1a0
[    0.364000]  ? kernel_init_freeable+0x189/0x20a
[    0.364000]  ? rest_init+0xc0/0xc0
[    0.364000]  ? kernel_init+0xa/0x100
[    0.364000]  ? ret_from_fork+0x25/0x30

I analyzed this memory leak in detail. I found that âAcpi-Stateâ cache and
âAcpi-Parseâ cache were merged because the size of cache objects was same
slab cache size.

I finally found âAcpi-Parseâ cache and âAcpi-ParseExtâ cache were leaked
using SLAB_NEVER_MERGE flag in kmem_cache_create() function.

Real ACPI cache leak point is as follows:
[    0.360101] ACPI: Added _OSI(Module Device)
[    0.360101] ACPI: Added _OSI(Processor Device)
[    0.360101] ACPI: Added _OSI(3.0 _SCP Extensions)
[    0.361043] ACPI: Added _OSI(Processor Aggregator Device)
[    0.364016] ACPI: Unable to start the ACPI Interpreter
[    0.365061] ACPI Error: Could not remove SCI handler (20170303/evmisc-281)
[    0.368174] kmem_cache_destroy Acpi-Parse: Slab cache still has objects
[    0.369332] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W
4.12.0-rc4-next-20170608+ #8
[    0.371256] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS
VirtualBox 12/01/2006
[    0.372000] Call Trace:
[    0.372000]  ? dump_stack+0x5c/0x81
[    0.372000]  ? kmem_cache_destroy+0x1aa/0x1c0
[    0.372000]  ? acpi_sleep_proc_init+0x27/0x27
[    0.372000]  ? acpi_os_delete_cache+0xa/0x10
[    0.372000]  ? acpi_ut_delete_caches+0x56/0x7b
[    0.372000]  ? acpi_terminate+0xa/0x14
[    0.372000]  ? acpi_init+0x2af/0x34f
[    0.372000]  ? __class_create+0x4c/0x80
[    0.372000]  ? video_setup+0x7f/0x7f
[    0.372000]  ? acpi_sleep_proc_init+0x27/0x27
[    0.372000]  ? do_one_initcall+0x4e/0x1a0
[    0.372000]  ? kernel_init_freeable+0x189/0x20a
[    0.372000]  ? rest_init+0xc0/0xc0
[    0.372000]  ? kernel_init+0xa/0x100
[    0.372000]  ? ret_from_fork+0x25/0x30
[    0.388039] kmem_cache_destroy Acpi-ParseExt: Slab cache still has objects
[    0.389063] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W
4.12.0-rc4-next-20170608+ #8
[    0.390557] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS
VirtualBox 12/01/2006
[    0.392000] Call Trace:
[    0.392000]  ? dump_stack+0x5c/0x81
[    0.392000]  ? kmem_cache_destroy+0x1aa/0x1c0
[    0.392000]  ? acpi_sleep_proc_init+0x27/0x27
[    0.392000]  ? acpi_os_delete_cache+0xa/0x10
[    0.392000]  ? acpi_ut_delete_caches+0x6d/0x7b
[    0.392000]  ? acpi_terminate+0xa/0x14
[    0.392000]  ? acpi_init+0x2af/0x34f
[    0.392000]  ? __class_create+0x4c/0x80
[    0.392000]  ? video_setup+0x7f/0x7f
[    0.392000]  ? acpi_sleep_proc_init+0x27/0x27
[    0.392000]  ? do_one_initcall+0x4e/0x1a0
[    0.392000]  ? kernel_init_freeable+0x189/0x20a
[    0.392000]  ? rest_init+0xc0/0xc0
[    0.392000]  ? kernel_init+0xa/0x100
[    0.392000]  ? 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_ut_delete_caches() function to delete local caches (acpi_gbl_namespace_
cache, state_cache, operand_cache, ps_node_cache, ps_node_ext_cache).

But the deletion codes in acpi_ut_delete_caches() function only delete
slab caches using kmem_cache_destroy() function, therefore the cache
objects should be flushed before acpi_ut_delete_caches() function.

âAcpi-Parseâ cache and âAcpi-ParseExtâ cache are used in an AML parse
function, acpi_ps_parse_loop(). The function should have flush codes to
handle an error state due to invalid AML codes.

This cache leak has a security threat because an old kernel (<= 4.9) shows
memory locations of kernel functions in stack dump. Some malicious users
could use this information to neutralize kernel ASLR.

To fix ACPI cache leak for enhancing security, I made a patch which has
flush codes in acpi_ps_parse_loop() function.

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

Thank you.

Signed-off-by: Seunghun Han <kkamagui@xxxxxxxxx>
---
Changes since v3: change control transfer according to reviewer's comments.
Changes since v2: merge flush code with existing code and change comments.
Changes since v1: move flush code to acpi_ps_complete_final_op() function.

 drivers/acpi/acpica/psobject.c | 53 +++++++++++++-----------------------------
 1 file changed, 16 insertions(+), 37 deletions(-)

diff --git a/drivers/acpi/acpica/psobject.c b/drivers/acpi/acpica/psobject.c
index 5bcb618..4539391 100644
--- a/drivers/acpi/acpica/psobject.c
+++ b/drivers/acpi/acpica/psobject.c
@@ -608,7 +608,8 @@ acpi_status
 acpi_ps_complete_final_op(struct acpi_walk_state *walk_state,
 			  union acpi_parse_object *op, acpi_status status)
 {
-	acpi_status status2;
+	acpi_status return_status = AE_OK;
+	u8 ascending = TRUE;
 
 	ACPI_FUNCTION_TRACE_PTR(ps_complete_final_op, walk_state);
 
@@ -622,7 +623,8 @@ acpi_ps_complete_final_op(struct acpi_walk_state *walk_state,
 			  op));
 	do {
 		if (op) {
-			if (walk_state->ascending_callback != NULL) {
+			if (ascending &&
+			    walk_state->ascending_callback != NULL) {
 				walk_state->op = op;
 				walk_state->op_info =
 				    acpi_ps_get_opcode_info(op->common.
@@ -644,49 +646,26 @@ acpi_ps_complete_final_op(struct acpi_walk_state *walk_state,
 				}
 
 				if (status == AE_CTRL_TERMINATE) {
-					status = AE_OK;
-
-					/* Clean up */
-					do {
-						if (op) {
-							status2 =
-							    acpi_ps_complete_this_op
-							    (walk_state, op);
-							if (ACPI_FAILURE
-							    (status2)) {
-								return_ACPI_STATUS
-								    (status2);
-							}
-						}
-
-						acpi_ps_pop_scope(&
-								  (walk_state->
-								   parser_state),
-								  &op,
-								  &walk_state->
-								  arg_types,
-								  &walk_state->
-								  arg_count);
-
-					} while (op);
-
-					return_ACPI_STATUS(status);
+					ascending = FALSE;
+					return_status = AE_CTRL_TERMINATE;
 				}
 
 				else if (ACPI_FAILURE(status)) {
 
 					/* First error is most important */
 
-					(void)
-					    acpi_ps_complete_this_op(walk_state,
-								     op);
-					return_ACPI_STATUS(status);
+					ascending = FALSE;
+					return_status = status;
 				}
 			}
 
-			status2 = acpi_ps_complete_this_op(walk_state, op);
-			if (ACPI_FAILURE(status2)) {
-				return_ACPI_STATUS(status2);
+			status = acpi_ps_complete_this_op(walk_state, op);
+			if (ACPI_FAILURE(status)) {
+				ascending = FALSE;
+				if (ACPI_SUCCESS(return_status) ||
+				    return_status == AE_CTRL_TERMINATE) {
+					return_status = status;
+				}
 			}
 		}
 
@@ -696,5 +675,5 @@ acpi_ps_complete_final_op(struct acpi_walk_state *walk_state,
 
 	} while (op);
 
-	return_ACPI_STATUS(status);
+	return_ACPI_STATUS(return_status);
 }
-- 
2.1.4