Patrick Georgi (pgeorgi@google.com) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/11519
-gerrit
commit 21716a5d3464e183c6fa08a215591a2aff5bc617 Author: Patrick Georgi patrick@georgi-clan.de Date: Sat Sep 5 20:21:24 2015 +0200
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 --- src/cpu/x86/smm/smmhandler.S | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)
diff --git a/src/cpu/x86/smm/smmhandler.S b/src/cpu/x86/smm/smmhandler.S index 7b70ce9..f2094ef 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 +78,39 @@ * * 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_NORTHBRIDGE_INTEL_NEHALEM) || \ + IS_ENABLED(CONFIG_NORTHBRIDGE_INTEL_GM45) || \ + IS_ENABLED(CONFIG_NORTHBRIDGE_INTEL_I945) + mov $LAPIC_BASE_MSR, %ecx + rdmsr + and $(~0xfff), %eax + sub $(SMM_START), %eax + cmp $(SMM_END - SMM_START), %eax + ja untampered_lapic +1: + // "Crash" + 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)