[PATCH] x86 emulator: Add IRET instruction

[Mohammed Gamal <m.gamal005@xxxxxxxxx>]

Ths patch adds IRET instruction (opcode 0xcf).
Currently, only IRET in real mode is emulated. Protected mode support is to be added later if needed.

Signed-off-by: Mohammed Gamal <m.gamal005@xxxxxxxxx>
---
 arch/x86/kvm/emulate.c |   63 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 62 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b38bd8b..ddc1da3 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1,5 +1,5 @@
 /******************************************************************************
- * emulate.c
+ i emulate.c
  *
  * Generic x86 (32-bit and 64-bit) instruction decoder and emulator.
  *
@@ -1778,6 +1778,61 @@ static int emulate_popa(struct x86_emulate_ctxt *ctxt,
 	return rc;
 }
 
+static int emulate_iret_real(struct x86_emulate_ctxt *ctxt,
+			     struct x86_emulate_ops *ops)
+{
+	struct decode_cache *c = &ctxt->decode;
+	int rc = X86EMUL_CONTINUE;
+	unsigned long temp_eip = 0;
+	unsigned long temp_eflags = 0;
+	/* TODO: Add stack limit check */
+
+	rc = emulate_pop(ctxt, ops, &temp_eip, c->op_bytes);
+
+	if (rc != X86EMUL_CONTINUE)
+		return rc;
+
+	if (temp_eip & ~0xffff) {
+		emulate_gp(ctxt, 0);
+		return X86EMUL_PROPAGATE_FAULT;
+	}
+
+	c->eip = temp_eip;
+
+	rc = emulate_pop_sreg(ctxt, ops, VCPU_SREG_CS);
+
+	if (rc != X86EMUL_CONTINUE)
+		return rc;
+
+	rc = emulate_pop(ctxt, ops, &temp_eflags, c->op_bytes);
+
+	if (rc != X86EMUL_CONTINUE)
+		return rc;
+
+	if (c->op_bytes == 4)
+		temp_eflags = ((temp_eflags & 0x257fd5) | (ctxt->eflags & 0x1a0000));
+	
+	ctxt->eflags = temp_eflags;
+
+	return rc;
+}
+
+static inline int emulate_iret(struct x86_emulate_ctxt *ctxt,
+				    struct x86_emulate_ops* ops)
+{
+	switch(ctxt->mode) {
+	case X86EMUL_MODE_REAL:
+		return emulate_iret_real(ctxt, ops);
+	case X86EMUL_MODE_VM86:
+	case X86EMUL_MODE_PROT16:
+	case X86EMUL_MODE_PROT32:
+	case X86EMUL_MODE_PROT64:
+	default:
+		/* iret from protected mode unimplemented yet */
+		return X86EMUL_UNHANDLEABLE;		
+	}
+}
+
 static inline int emulate_grp1a(struct x86_emulate_ctxt *ctxt,
 				struct x86_emulate_ops *ops)
 {
@@ -2910,6 +2965,12 @@ special_insn:
 		if (rc != X86EMUL_CONTINUE)
 			goto done;
 		break;
+	case 0xcf:		/* iret */
+		rc = emulate_iret(ctxt, ops);
+
+		if (rc != X86EMUL_CONTINUE)
+			goto done;
+		break;
 	case 0xd0 ... 0xd1:	/* Grp2 */
 		c->src.val = 1;
 		emulate_grp2(ctxt);
-- 
1.7.0.4

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