[PATCH 16/20] KVM: x86 emulator: Check CPL level during privilege instruction emulation

Avi Kivity
2010-02-17T13:45:26Z

From: Gleb Natapov <gleb@redhat.com>

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>
---
arch/x86/kvm/emulate.c | 35 ++++++++++++++++++++---------------
1 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 1782387..d632111 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;

--
1.6.5.3