kvm: x86: fix RSM when PCID is non-zero

rsm_load_state_64() and rsm_enter_protected_mode() load CR3, then
CR4 & ~PCIDE, then CR0, then CR4.

However, setting CR4.PCIDE fails if CR3[11:0] != 0.  It's probably easier
in the long run to replace rsm_enter_protected_mode() with an emulator
callback that sets all the special registers (like KVM_SET_SREGS would
do).  For now, set the PCID field of CR3 only after CR4.PCIDE is 1.
Reported-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Fixes: 660a5d51
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

CVE-2017-5754
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/kvm/emulate.c

@@ -2383,9 +2383,21 @@ static int rsm_load_seg_64(struct x86_emulate_ctxt *ctxt, u64 smbase, int n)
 }
 
 static int rsm_enter_protected_mode(struct x86_emulate_ctxt *ctxt,
-				     u64 cr0, u64 cr4)
+				    u64 cr0, u64 cr3, u64 cr4)
 {
 	int bad;
+	u64 pcid;
+
+	/* In order to later set CR4.PCIDE, CR3[11:0] must be zero.  */
+	pcid = 0;
+	if (cr4 & X86_CR4_PCIDE) {
+		pcid = cr3 & 0xfff;
+		cr3 &= ~0xfff;
+	}
+
+	bad = ctxt->ops->set_cr(ctxt, 3, cr3);
+	if (bad)
+		return X86EMUL_UNHANDLEABLE;
 
 	/*
 	 * First enable PAE, long mode needs it before CR0.PG = 1 is set.
@@ -2404,6 +2416,12 @@ static int rsm_enter_protected_mode(struct x86_emulate_ctxt *ctxt,
 		bad = ctxt->ops->set_cr(ctxt, 4, cr4);
 		if (bad)
 			return X86EMUL_UNHANDLEABLE;
+		if (pcid) {
+			bad = ctxt->ops->set_cr(ctxt, 3, cr3 | pcid);
+			if (bad)
+				return X86EMUL_UNHANDLEABLE;
+		}
+
 	}
 
 	return X86EMUL_CONTINUE;
@@ -2414,11 +2432,11 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt, u64 smbase)
 	struct desc_struct desc;
 	struct desc_ptr dt;
 	u16 selector;
-	u32 val, cr0, cr4;
+	u32 val, cr0, cr3, cr4;
 	int i;
 
 	cr0 =                      GET_SMSTATE(u32, smbase, 0x7ffc);
-	ctxt->ops->set_cr(ctxt, 3, GET_SMSTATE(u32, smbase, 0x7ff8));
+	cr3 =                      GET_SMSTATE(u32, smbase, 0x7ff8);
 	ctxt->eflags =             GET_SMSTATE(u32, smbase, 0x7ff4) | X86_EFLAGS_FIXED;
 	ctxt->_eip =               GET_SMSTATE(u32, smbase, 0x7ff0);
 
@@ -2460,14 +2478,14 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt, u64 smbase)
 
 	ctxt->ops->set_smbase(ctxt, GET_SMSTATE(u32, smbase, 0x7ef8));
 
-	return rsm_enter_protected_mode(ctxt, cr0, cr4);
+	return rsm_enter_protected_mode(ctxt, cr0, cr3, cr4);
 }
 
 static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase)
 {
 	struct desc_struct desc;
 	struct desc_ptr dt;
-	u64 val, cr0, cr4;
+	u64 val, cr0, cr3, cr4;
 	u32 base3;
 	u16 selector;
 	int i, r;
@@ -2484,7 +2502,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase)
 	ctxt->ops->set_dr(ctxt, 7, (val & DR7_VOLATILE) | DR7_FIXED_1);
 
 	cr0 =                       GET_SMSTATE(u64, smbase, 0x7f58);
-	ctxt->ops->set_cr(ctxt, 3,  GET_SMSTATE(u64, smbase, 0x7f50));
+	cr3 =                       GET_SMSTATE(u64, smbase, 0x7f50);
 	cr4 =                       GET_SMSTATE(u64, smbase, 0x7f48);
 	ctxt->ops->set_smbase(ctxt, GET_SMSTATE(u32, smbase, 0x7f00));
 	val =                       GET_SMSTATE(u64, smbase, 0x7ed0);
@@ -2512,7 +2530,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt, u64 smbase)
 	dt.address =                GET_SMSTATE(u64, smbase, 0x7e68);
 	ctxt->ops->set_gdt(ctxt, &dt);
 
-	r = rsm_enter_protected_mode(ctxt, cr0, cr4);
+	r = rsm_enter_protected_mode(ctxt, cr0, cr3, cr4);
 	if (r != X86EMUL_CONTINUE)
 		return r;