Patch "KVM: X86: Fix operand/address-size during instruction decoding" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

KVM: X86: Fix operand/address-size during instruction decoding

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-fix-operand-address-size-during-instruction-decoding.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Wanpeng Li <[email protected]>
Date: Sun, 5 Nov 2017 16:54:47 -0800
Subject: KVM: X86: Fix operand/address-size during instruction decoding

From: Wanpeng Li <[email protected]>

[ Upstream commit 3853be2603191829b442b64dac6ae8ba0c027bf9 ]

Pedro reported:
During tests that we conducted on KVM, we noticed that executing a "PUSH %ES" instruction under KVM produces different results on both memory and the SP register depending on whether EPT support is enabled. With EPT the SP is reduced by 4 bytes (and the written value is 0-padded) but without EPT support it is only reduced by 2 bytes. The difference can be observed when the CS.DB field is 1 (32-bit) but not when it's 0 (16-bit).

The internal segment descriptor cache exist even in real/vm8096 mode. The CS.D also should be respected instead of just default operand/address-size/66H prefix/67H prefix during instruction decoding. This patch fixes it by also adjusting operand/address-size according to CS.D.

---
 arch/x86/kvm/emulate.c |    7 +++++++
 1 file changed, 7 insertions(+)

@@ -4990,6 +4990,8 @@ int x86_decode_insn(struct x86_emulate_c
 	bool op_prefix = false;
 	bool has_seg_override = false;
 	struct opcode opcode;
+	u16 dummy;
+	struct desc_struct desc;
 
 	ctxt->memop.type = OP_NONE;
 	ctxt->memopp = NULL;

@@ -5008,6 +5010,11 @@ int x86_decode_insn(struct x86_emulate_c
 	switch (mode) {
 	case X86EMUL_MODE_REAL:
 	case X86EMUL_MODE_VM86:
+		def_op_bytes = def_ad_bytes = 2;
+		ctxt->ops->get_segment(ctxt, &dummy, &desc, NULL, VCPU_SREG_CS);
+		if (desc.d)
+			def_op_bytes = def_ad_bytes = 4;
+		break;
 	case X86EMUL_MODE_PROT16:
 		def_op_bytes = def_ad_bytes = 2;
 		break;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-x86-don-t-re-execute-instruction-when-not-passing-cr2-value.patch queue-4.9/kvm-x86-ioapic-preserve-read-only-values-in-the-redirection-table.patch queue-4.9/kvm-vmx-fix-rflags-cache-during-vcpu-reset.patch queue-4.9/kvm-x86-fix-operand-address-size-during-instruction-decoding.patch queue-4.9/kvm-x86-emulator-return-to-user-mode-on-l1-cpl-0-emulation-failure.patch queue-4.9/kvm-x86-fix-softlockup-when-get-the-current-kvmclock.patch queue-4.9/kvm-x86-ioapic-clear-remote-irr-when-entry-is-switched-to-edge-triggered.patch