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>
----
Changes from v1:
- Corrected handling of eflags
---
arch/x86/kvm/emulate.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 69 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b38bd8b..e45fd28 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1778,6 +1778,69 @@ 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;
+ unsigned long mask = EFLG_CF | EFLG_PF | EFLG_AF | EFLG_ZF | EFLG_SF | EFLG_TF |
+ EFLG_IF | EFLG_DF | EFLG_OF | EFLG_IOPL | EFLG_NT | EFLG_RF |
+ EFLG_AC | EFLG_ID | (1 << 1); /* Last one is the reserved bit */
+ unsigned long vm86_mask = EFLG_VM | EFLG_VIF | EFLG_VIP;
+
+ /* 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 & mask) | (ctxt->eflags & vm86_mask));
+ ctxt->eflags = temp_eflags;
+ } else if (c->op_bytes == 2) {
+ temp_eflags &= ~0xfffd; /* Do not clear reserved bit 1 */
+ 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 +2973,12 @@ 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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