Vulnerability: The acpi_ds_create_operands() function in drivers/acpi/acpica/dsutils.c in the Linux kernel through 4.12.9 does not flush the operand cache and causes a kernel stack dump, which allows local users to obtain sensitive information from kernel memory and bypass the KASLR protection mechanism (in the kernel through 4.9) via a crafted ACPI table.
Vulnerability ID: CVE-2017-13693
CWE: CWE-200
Severity score: 6.9
Project: https://github.com/acpica/acpica
Published: 2017-08-25
File: source/components/dispatcher/dsutils.c
Commit message: acpi: acpica: fix acpi operand cache leak in dswstate.c

I found an ACPI cache leak in ACPI early termination and boot continuing case.

When early termination occurs due to malicious ACPI table, Linux kernel
terminates ACPI function and continues to boot process. While kernel terminates
ACPI function, kmem_cache_destroy() reports Acpi-Operand cache leak.

Boot log of ACPI operand cache leak is as follows:
>[    0.585957] ACPI: Added _OSI(Module Device)
>[    0.587218] ACPI: Added _OSI(Processor Device)
>[    0.588530] ACPI: Added _OSI(3.0 _SCP Extensions)
>[    0.589790] ACPI: Added _OSI(Processor Aggregator Device)
>[    0.591534] ACPI Error: Illegal I/O port address/length above 64K: C806E00000004002/0x2 (20170303/hwvalid-155)
>[    0.594351] ACPI Exception: AE_LIMIT, Unable to initialize fixed events (20170303/evevent-88)
>[    0.597858] ACPI: Unable to start the ACPI Interpreter
>[    0.599162] ACPI Error: Could not remove SCI handler (20170303/evmisc-281)
>[    0.601836] kmem_cache_destroy Acpi-Operand: Slab cache still has objects
>[    0.603556] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc5 #26
>[    0.605159] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>[    0.609177] Call Trace:
>[    0.610063]  ? dump_stack+0x5c/0x81
>[    0.611118]  ? kmem_cache_destroy+0x1aa/0x1c0
>[    0.612632]  ? acpi_sleep_proc_init+0x27/0x27
>[    0.613906]  ? acpi_os_delete_cache+0xa/0x10
>[    0.617986]  ? acpi_ut_delete_caches+0x3f/0x7b
>[    0.619293]  ? acpi_terminate+0xa/0x14
>[    0.620394]  ? acpi_init+0x2af/0x34f
>[    0.621616]  ? __class_create+0x4c/0x80
>[    0.623412]  ? video_setup+0x7f/0x7f
>[    0.624585]  ? acpi_sleep_proc_init+0x27/0x27
>[    0.625861]  ? do_one_initcall+0x4e/0x1a0
>[    0.627513]  ? kernel_init_freeable+0x19e/0x21f
>[    0.628972]  ? rest_init+0x80/0x80
>[    0.630043]  ? kernel_init+0xa/0x100
>[    0.631084]  ? ret_from_fork+0x25/0x30
>[    0.633343] vgaarb: loaded
>[    0.635036] EDAC MC: Ver: 3.0.0
>[    0.638601] PCI: Probing PCI hardware
>[    0.639833] PCI host bridge to bus 0000:00
>[    0.641031] pci_bus 0000:00: root bus resource [io  0x0000-0xffff]
> ... Continue to boot and log is omitted ...

I analyzed this memory leak in detail and found acpi_ds_obj_stack_pop_and_
delete() function miscalculated the top of the stack. acpi_ds_obj_stack_push()
function uses walk_state->operand_index for start position of the top, but
acpi_ds_obj_stack_pop_and_delete() function considers index 0 for it.
Therefore, this causes acpi operand memory leak.

This cache leak causes 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.

I made a patch to fix ACPI operand cache leak.

Signed-off-by: Seunghun Han <kkamagui@gmail.com>
Commit author: Seunghun Han

Vulnerable version (before fix):
 AcpiDsCreateOperands (     ACPI_PARSE_OBJECT       *Arguments[ACPI_OBJ_NUM_OPERANDS];     UINT32                  ArgCount = 0;     UINT32                  Index = WalkState->NumOperands;     UINT32                  i;   AcpiDsCreateOperands (      /* Create the interpreter arguments, in reverse order */      Index--;     for (i = 0; i < ArgCount; i++)     { AcpiDsCreateOperands (      * pop everything off of the operand stack and delete those      * objects      */     AcpiDsObjStackPopAndDelete (ArgCount, WalkState);      ACPI_EXCEPTION ((AE_INFO, Status, "While creating Arg %u", Index));     return_ACPI_STATUS (Status);

Fixed version (after fix):
 AcpiDsCreateOperands (     ACPI_PARSE_OBJECT       *Arguments[ACPI_OBJ_NUM_OPERANDS];     UINT32                  ArgCount = 0;     UINT32                  Index = WalkState->NumOperands;     UINT32                  PrevNumOperands = WalkState->NumOperands;     UINT32                  NewNumOperands;     UINT32                  i;   AcpiDsCreateOperands (      /* Create the interpreter arguments, in reverse order */      NewNumOperands = Index;     Index--;     for (i = 0; i < ArgCount; i++)     { AcpiDsCreateOperands (      * pop everything off of the operand stack and delete those      * objects      */     WalkState->NumOperands = i;     AcpiDsObjStackPopAndDelete (NewNumOperands, WalkState);      /* Restore operand count */     WalkState->NumOperands = PrevNumOperands;      ACPI_EXCEPTION ((AE_INFO, Status, "While creating Arg %u", Index));     return_ACPI_STATUS (Status);

Patch:
patch: @@ -868,6 +868,8 @@ AcpiDsCreateOperands (
     ACPI_PARSE_OBJECT       *Arguments[ACPI_OBJ_NUM_OPERANDS];
     UINT32                  ArgCount = 0;
     UINT32                  Index = WalkState->NumOperands;
+    UINT32                  PrevNumOperands = WalkState->NumOperands;
+    UINT32                  NewNumOperands;
     UINT32                  i;
 
 
@@ -900,6 +902,7 @@ AcpiDsCreateOperands (
 
     /* Create the interpreter arguments, in reverse order */
 
+    NewNumOperands = Index;
     Index--;
     for (i = 0; i < ArgCount; i++)
     {
@@ -927,7 +930,11 @@ AcpiDsCreateOperands (
      * pop everything off of the operand stack and delete those
      * objects
      */
-    AcpiDsObjStackPopAndDelete (ArgCount, WalkState);
+    WalkState->NumOperands = i;
+    AcpiDsObjStackPopAndDelete (NewNumOperands, WalkState);
+
+    /* Restore operand count */
+    WalkState->NumOperands = PrevNumOperands;
 
     ACPI_EXCEPTION ((AE_INFO, Status, "While creating Arg %u", Index));
     return_ACPI_STATUS (Status);
path: source/components/dispatcher/dsutils.c