From ce2564ac519fd974eeaa070ccb30d5a12e0c3334 Mon Sep 17 00:00:00 2001
From: Patrick Georgi <patrick@georgi-clan.de>
Date: Sat, 5 Sep 2015 20:21:24 +0200
Subject: smmhandler: on i945..nehalem, crash if LAPIC overlaps with ASEG

This mitigates the Memory Sinkhole issue (described on
https://github.com/xoreaxeaxeax/sinkhole) by checking for the issue and
crashing the system explicitly if LAPIC overlaps ASEG.
This needs to happen without a data access (only code fetches) because
data accesses could be tampered with.

Don't try to recover because, if somebody tried to do shenanigans like
these, we have to expect more.
Sandybridge is safe because it does the same test in hardware, and
crashes. Newer chipsets presumably do the same.

This needs to be extended to deal with overlapping TSEG as well.

Change-Id: I508c0b10ab88779da81d18a94b08dcfeca6f5a6f
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/11519
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
---
 src/cpu/x86/Kconfig          |  7 +++++++
 src/cpu/x86/smm/smmhandler.S | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

(limited to 'src')

diff --git a/src/cpu/x86/Kconfig b/src/cpu/x86/Kconfig
index 9e5f6155fe..131cbf24bb 100644
--- a/src/cpu/x86/Kconfig
+++ b/src/cpu/x86/Kconfig
@@ -89,6 +89,13 @@ config SMM_MODULE_HEAP_SIZE
 	  This option determines the size of the heap within the SMM handler
 	  modules.
 
+config SMM_LAPIC_REMAP_MITIGATION
+	bool
+	default y if NORTHBRIDGE_INTEL_I945
+	default y if NORTHBRIDGE_INTEL_GM45
+	default y if NORTHBRIDGE_INTEL_NEHALEM
+	default n
+
 config X86_AMD_FIXED_MTRRS
 	bool
 	default n
diff --git a/src/cpu/x86/smm/smmhandler.S b/src/cpu/x86/smm/smmhandler.S
index 7b70ce9585..9cc6582ffe 100644
--- a/src/cpu/x86/smm/smmhandler.S
+++ b/src/cpu/x86/smm/smmhandler.S
@@ -25,6 +25,10 @@
  * to 64k if we can though.
  */
 
+#include <kconfig.h>
+#include <config.h>
+#define LAPIC_BASE_MSR 0x1b
+
 /*
  * +--------------------------------+ 0xaffff
  * |  Save State Map Node 0         |
@@ -74,8 +78,43 @@
  *
  * All the bad magic is not all that bad after all.
  */
+#define SMM_START 0xa0000
+#define SMM_END   0xb0000
+#if SMM_END <= SMM_START
+#error invalid SMM configuration
+#endif
 .global smm_handler_start
 smm_handler_start:
+#if IS_ENABLED(CONFIG_SMM_LAPIC_REMAP_MITIGATION)
+	/* Check if the LAPIC register block overlaps with SMM.
+	 * This block needs to work without data accesses because they
+	 * may be routed into the LAPIC register block.
+	 * Code accesses, on the other hand, are never routed to LAPIC,
+	 * which is what makes this work in the first place.
+	 */
+	mov	$LAPIC_BASE_MSR, %ecx
+	rdmsr
+	and	$(~0xfff), %eax
+	sub	$(SMM_START), %eax
+	cmp	$(SMM_END - SMM_START), %eax
+	ja	untampered_lapic
+1:
+	/* emit "Crash" on serial */
+	mov	$(CONFIG_TTYS0_BASE), %dx
+	mov	$'C', %al
+	out	%al, (%dx)
+	mov	$'r', %al
+	out	%al, (%dx)
+	mov	$'a', %al
+	out	%al, (%dx)
+	mov	$'s', %al
+	out	%al, (%dx)
+	mov	$'h', %al
+	out	%al, (%dx)
+	/* now crash for real */
+	ud2
+untampered_lapic:
+#endif
 	movw    $(smm_gdtptr16 - smm_handler_start + SMM_HANDLER_OFFSET), %bx
 	data32  lgdt %cs:(%bx)
 
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