KVM: x86 emulator: Check CPL level during privilege instruction emulation

Add CPL checking in case emulator is tricked into emulating
privilege instruction from userspace.

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

1 files changed, 20 insertions, 15 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 1782387c069e..d63211169ac1 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -76,6 +76,7 @@
 #define GroupDual   (1<<15)     /* Alternate decoding of mod == 3 */
 #define GroupMask   0xff        /* Group number stored in bits 0:7 */
 /* Misc flags */
+#define Priv        (1<<27) /* instruction generates #GP if current CPL != 0 */
 #define No64        (1<<28)
 /* Source 2 operand type */
 #define Src2None    (0<<29)
@@ -211,7 +212,7 @@ static u32 opcode_table[256] = {
         SrcNone | ByteOp | ImplicitOps, SrcNone | ImplicitOps,
         /* 0xF0 - 0xF7 */
         0, 0, 0, 0,
-        ImplicitOps, ImplicitOps, Group | Group3_Byte, Group | Group3,
+        ImplicitOps | Priv, ImplicitOps, Group | Group3_Byte, Group | Group3,
         /* 0xF8 - 0xFF */
         ImplicitOps, 0, ImplicitOps, ImplicitOps,
         ImplicitOps, ImplicitOps, Group | Group4, Group | Group5,
@@ -219,16 +220,20 @@ static u32 opcode_table[256] = {
 
 static u32 twobyte_table[256] = {
         /* 0x00 - 0x0F */
-        0, Group | GroupDual | Group7, 0, 0, 0, ImplicitOps, ImplicitOps, 0,
-        ImplicitOps, ImplicitOps, 0, 0, 0, ImplicitOps | ModRM, 0, 0,
+        0, Group | GroupDual | Group7, 0, 0,
+        0, ImplicitOps, ImplicitOps | Priv, 0,
+        ImplicitOps | Priv, ImplicitOps | Priv, 0, 0,
+        0, ImplicitOps | ModRM, 0, 0,
         /* 0x10 - 0x1F */
         0, 0, 0, 0, 0, 0, 0, 0, ImplicitOps | ModRM, 0, 0, 0, 0, 0, 0, 0,
         /* 0x20 - 0x2F */
-        ModRM | ImplicitOps, ModRM, ModRM | ImplicitOps, ModRM, 0, 0, 0, 0,
+        ModRM | ImplicitOps | Priv, ModRM | Priv,
+        ModRM | ImplicitOps | Priv, ModRM | Priv,
+        0, 0, 0, 0,
         0, 0, 0, 0, 0, 0, 0, 0,
         /* 0x30 - 0x3F */
-        ImplicitOps, 0, ImplicitOps, 0,
-        ImplicitOps, ImplicitOps, 0, 0,
+        ImplicitOps | Priv, 0, ImplicitOps | Priv, 0,
+        ImplicitOps, ImplicitOps | Priv, 0, 0,
         0, 0, 0, 0, 0, 0, 0, 0,
         /* 0x40 - 0x47 */
         DstReg | SrcMem | ModRM | Mov, DstReg | SrcMem | ModRM | Mov,
@@ -322,9 +327,9 @@ static u32 group_table[] = {
         SrcMem | ModRM | Stack, 0,
         SrcMem | ModRM | Stack, 0, SrcMem | ModRM | Stack, 0,
         [Group7*8] =
-        0, 0, ModRM | SrcMem, ModRM | SrcMem,
+        0, 0, ModRM | SrcMem | Priv, ModRM | SrcMem | Priv,
         SrcNone | ModRM | DstMem | Mov, 0,
-        SrcMem16 | ModRM | Mov, SrcMem | ModRM | ByteOp,
+        SrcMem16 | ModRM | Mov | Priv, SrcMem | ModRM | ByteOp | Priv,
         [Group8*8] =
         0, 0, 0, 0,
         DstMem | SrcImmByte | ModRM, DstMem | SrcImmByte | ModRM,
@@ -335,7 +340,7 @@ static u32 group_table[] = {
 
 static u32 group2_table[] = {
         [Group7*8] =
-        SrcNone | ModRM, 0, 0, SrcNone | ModRM,
+        SrcNone | ModRM | Priv, 0, 0, SrcNone | ModRM,
         SrcNone | ModRM | DstMem | Mov, 0,
         SrcMem16 | ModRM | Mov, 0,
         [Group9*8] =
@@ -1700,12 +1705,6 @@ emulate_sysexit(struct x86_emulate_ctxt *ctxt)
                 return -1;
         }
 
-        /* sysexit must be called from CPL 0 */
-        if (kvm_x86_ops->get_cpl(ctxt->vcpu) != 0) {
-                kvm_inject_gp(ctxt->vcpu, 0);
-                return -1;
-        }
-
         setup_syscalls_segments(ctxt, &cs, &ss);
 
         if ((c->rex_prefix & 0x8) != 0x0)
@@ -1820,6 +1819,12 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
         memcpy(c->regs, ctxt->vcpu->arch.regs, sizeof c->regs);
         saved_eip = c->eip;
 
+        /* Privileged instruction can be executed only in CPL=0 */
+        if ((c->d & Priv) && kvm_x86_ops->get_cpl(ctxt->vcpu)) {
+                kvm_inject_gp(ctxt->vcpu, 0);
+                goto done;
+        }
+
         if (((c->d & ModRM) && (c->modrm_mod != 3)) || (c->d & MemAbs))
                 memop = c->modrm_ea;