KVM: x86: check CS.DPL against RPL during task switch

Table 7-1 of the SDM mentions a check that the code segment's
DPL must match the selector's RPL.  This was not done by KVM,
fix it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 17 insertions, 14 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 47e716ef46b7..2fa7ab069817 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1411,7 +1411,7 @@ static int write_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 
 /* Does not support long mode */
 static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
-                                     u16 selector, int seg, u8 cpl)
+                                     u16 selector, int seg, u8 cpl, bool in_task_switch)
 {
         struct desc_struct seg_desc, old_desc;
         u8 dpl, rpl;
@@ -1486,6 +1486,9 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
                         goto exception;
                 break;
         case VCPU_SREG_CS:
+                if (in_task_switch && rpl != dpl)
+                        goto exception;
+
                 if (!(seg_desc.type & 8))
                         goto exception;
 
@@ -1547,7 +1550,7 @@ static int load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
                                    u16 selector, int seg)
 {
         u8 cpl = ctxt->ops->cpl(ctxt);
-        return __load_segment_descriptor(ctxt, selector, seg, cpl);
+        return __load_segment_descriptor(ctxt, selector, seg, cpl, false);
 }
 
 static void write_register_operand(struct operand *op)
@@ -2440,19 +2443,19 @@ static int load_state_from_tss16(struct x86_emulate_ctxt *ctxt,
          * Now load segment descriptors. If fault happens at this stage
          * it is handled in a context of new task
          */
-        ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
 
@@ -2577,25 +2580,25 @@ static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,
          * Now load segment descriptors. If fault happenes at this stage
          * it is handled in a context of new task
          */
-        ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;
-        ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl);
+        ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl, true);
         if (ret != X86EMUL_CONTINUE)
                 return ret;