KVM: x86 emulator: Fix popf emulation

POPF behaves differently depending on current CPU mode. Emulate correct
logic to prevent guest from changing flags that it can't change otherwise.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 54 insertions, 1 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 296e8519dc53..1782387c069e 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -343,11 +343,18 @@ static u32 group2_table[] = {
 };
 
 /* EFLAGS bit definitions. */
+#define EFLG_ID (1<<21)
+#define EFLG_VIP (1<<20)
+#define EFLG_VIF (1<<19)
+#define EFLG_AC (1<<18)
 #define EFLG_VM (1<<17)
 #define EFLG_RF (1<<16)
+#define EFLG_IOPL (3<<12)
+#define EFLG_NT (1<<14)
 #define EFLG_OF (1<<11)
 #define EFLG_DF (1<<10)
 #define EFLG_IF (1<<9)
+#define EFLG_TF (1<<8)
 #define EFLG_SF (1<<7)
 #define EFLG_ZF (1<<6)
 #define EFLG_AF (1<<4)
@@ -1214,6 +1221,49 @@ static int emulate_pop(struct x86_emulate_ctxt *ctxt,
         return rc;
 }
 
+static int emulate_popf(struct x86_emulate_ctxt *ctxt,
+                       struct x86_emulate_ops *ops,
+                       void *dest, int len)
+{
+        int rc;
+        unsigned long val, change_mask;
+        int iopl = (ctxt->eflags & X86_EFLAGS_IOPL) >> IOPL_SHIFT;
+        int cpl = kvm_x86_ops->get_cpl(ctxt->vcpu);
+
+        rc = emulate_pop(ctxt, ops, &val, len);
+        if (rc != X86EMUL_CONTINUE)
+                return rc;
+
+        change_mask = EFLG_CF | EFLG_PF | EFLG_AF | EFLG_ZF | EFLG_SF | EFLG_OF
+                | EFLG_TF | EFLG_DF | EFLG_NT | EFLG_RF | EFLG_AC | EFLG_ID;
+
+        switch(ctxt->mode) {
+        case X86EMUL_MODE_PROT64:
+        case X86EMUL_MODE_PROT32:
+        case X86EMUL_MODE_PROT16:
+                if (cpl == 0)
+                        change_mask |= EFLG_IOPL;
+                if (cpl <= iopl)
+                        change_mask |= EFLG_IF;
+                break;
+        case X86EMUL_MODE_VM86:
+                if (iopl < 3) {
+                        kvm_inject_gp(ctxt->vcpu, 0);
+                        return X86EMUL_PROPAGATE_FAULT;
+                }
+                change_mask |= EFLG_IF;
+                break;
+        default: /* real mode */
+                change_mask |= (EFLG_IOPL | EFLG_IF);
+                break;
+        }
+
+        *(unsigned long *)dest =
+                (ctxt->eflags & ~change_mask) | (val & change_mask);
+
+        return rc;
+}
+
 static void emulate_push_sreg(struct x86_emulate_ctxt *ctxt, int seg)
 {
         struct decode_cache *c = &ctxt->decode;
@@ -2099,7 +2149,10 @@ special_insn:
                 c->dst.type = OP_REG;
                 c->dst.ptr = (unsigned long *) &ctxt->eflags;
                 c->dst.bytes = c->op_bytes;
-                goto pop_instruction;
+                rc = emulate_popf(ctxt, ops, &c->dst.val, c->op_bytes);
+                if (rc != X86EMUL_CONTINUE)
+                        goto done;
+                break;
         case 0xa0 ... 0xa1:     /* mov */
                 c->dst.ptr = (unsigned long *)&c->regs[VCPU_REGS_RAX];
                 c->dst.val = c->src.val;