Vulnerability: The acpi_ns_evaluate() function in drivers/acpi/acpica/nseval.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-2017-13695
CWE: CWE-200
Severity score: 2.9
Project: https://github.com/acpica/acpica
Published: 2017-08-25
File: source/components/namespace/nseval.c
Commit message: acpi: acpica: fix acpi operand cache leak in nseval.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:
>[    0.464168] ACPI: Added _OSI(Module Device)
>[    0.467022] ACPI: Added _OSI(Processor Device)
>[    0.469376] ACPI: Added _OSI(3.0 _SCP Extensions)
>[    0.471647] ACPI: Added _OSI(Processor Aggregator Device)
>[    0.477997] ACPI Error: Null stack entry at ffff880215c0aad8 (20170303/exresop-174)
>[    0.482706] ACPI Exception: AE_AML_INTERNAL, While resolving operands for [OpcodeName unavailable] (20170303/dswexec-461)
>[    0.487503] ACPI Error: Method parse/execution failed [\DBG] (Node ffff88021710ab40), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.492136] ACPI Error: Method parse/execution failed [\_SB._INI] (Node ffff88021710a618), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.497683] ACPI: Interpreter enabled
>[    0.499385] ACPI: (supports S0)
>[    0.501151] ACPI: Using IOAPIC for interrupt routing
>[    0.503342] ACPI Error: Null stack entry at ffff880215c0aad8 (20170303/exresop-174)
>[    0.506522] ACPI Exception: AE_AML_INTERNAL, While resolving operands for [OpcodeName unavailable] (20170303/dswexec-461)
>[    0.510463] ACPI Error: Method parse/execution failed [\DBG] (Node ffff88021710ab40), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.514477] ACPI Error: Method parse/execution failed [\_PIC] (Node ffff88021710ab18), AE_AML_INTERNAL (20170303/psparse-543)
>[    0.518867] ACPI Exception: AE_AML_INTERNAL, Evaluating _PIC (20170303/bus-991)
>[    0.522384] kmem_cache_destroy Acpi-Operand: Slab cache still has objects
>[    0.524597] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc5 #26
>[    0.526795] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
>[    0.529668] Call Trace:
>[    0.530811]  ? dump_stack+0x5c/0x81
>[    0.532240]  ? kmem_cache_destroy+0x1aa/0x1c0
>[    0.533905]  ? acpi_os_delete_cache+0xa/0x10
>[    0.535497]  ? acpi_ut_delete_caches+0x3f/0x7b
>[    0.537237]  ? acpi_terminate+0xa/0x14
>[    0.538701]  ? acpi_init+0x2af/0x34f
>[    0.540008]  ? acpi_sleep_proc_init+0x27/0x27
>[    0.541593]  ? do_one_initcall+0x4e/0x1a0
>[    0.543008]  ? kernel_init_freeable+0x19e/0x21f
>[    0.546202]  ? rest_init+0x80/0x80
>[    0.547513]  ? kernel_init+0xa/0x100
>[    0.548817]  ? ret_from_fork+0x25/0x30
>[    0.550587] vgaarb: loaded
>[    0.551716] EDAC MC: Ver: 3.0.0
>[    0.553744] PCI: Probing PCI hardware
>[    0.555038] PCI host bridge to bus 0000:00
> ... Continue to boot and log is omitted ...

I analyzed this memory leak in detail and found AcpiNsEvaluate() function
only removes Info->ReturnObject in AE_CTRL_RETURN_VALUE case. But, when errors
occur, the status value is not AE_CTRL_RETURN_VALUE, and Info->ReturnObject is
also not null. 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):
 AcpiNsEvaluate (          Status = AE_OK;     }      ACPI_DEBUG_PRINT ((ACPI_DB_NAMES,         "*** Completed evaluation of object %s ***\n",

Fixed version (after fix):
 AcpiNsEvaluate (          Status = AE_OK;     }     else if (ACPI_FAILURE(Status))      {         /* If ReturnObject exists, delete it */          if (Info->ReturnObject)          {             AcpiUtRemoveReference (Info->ReturnObject);             Info->ReturnObject = NULL;         }     }      ACPI_DEBUG_PRINT ((ACPI_DB_NAMES,         "*** Completed evaluation of object %s ***\n",

Patch:
patch: @@ -428,6 +428,16 @@ AcpiNsEvaluate (
 
         Status = AE_OK;
     }
+    else if (ACPI_FAILURE(Status)) 
+    {
+        /* If ReturnObject exists, delete it */
+
+        if (Info->ReturnObject) 
+        {
+            AcpiUtRemoveReference (Info->ReturnObject);
+            Info->ReturnObject = NULL;
+        }
+    }
 
     ACPI_DEBUG_PRINT ((ACPI_DB_NAMES,
         "*** Completed evaluation of object %s ***\n",
path: source/components/namespace/nseval.c