[PATCH 1/3] KVM: x86: Emulator flag for instruction with no big real mode

Nadav Amit
2014-06-18T14:19:54Z

Certain instructions, such as monitor and xsave do not support big real mode
and cause a #GP exception if any of the accessed bytes effective address are
not within [0, 0xffff]. This patch introduces a flag to mark these
instructions, including the necassary checks.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
arch/x86/kvm/emulate.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index e4e833d..f90194d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -162,6 +162,7 @@
#define NoWrite ((u64)1 << 45) /* No writeback */
#define SrcWrite ((u64)1 << 46) /* Write back src operand */
#define NoMod ((u64)1 << 47) /* Mod field is ignored */
+#define NoBigReal ((u64)1 << 48) /* No big real mode */

#define DstXacc (DstAccLo | SrcAccHi | SrcWrite)

@@ -651,7 +652,12 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
if (!fetch && (desc.type & 8) && !(desc.type & 2))
goto bad;
lim = desc_limit_scaled(&desc);
- if ((desc.type & 8) || !(desc.type & 4)) {
+ if ((ctxt->mode == X86EMUL_MODE_REAL) && !fetch &&
+ (ctxt->d & NoBigReal)) {
+ /* la is between zero and 0xffff */
+ if (la > 0xffff || (u32)(la + size - 1) > 0xffff)
+ goto bad;
+ } else if ((desc.type & 8) || !(desc.type & 4)) {
/* expand-up segment */
if (addr.ea > lim || (u32)(addr.ea + size - 1) > lim)
goto bad;
--
1.9.1