x86/hvm: Introduce control register handling for CET

Allow CR4.CET to be set, based on the CPUID policy (although these bits are
not selectable yet for VMs).  CR4.CET needs interlocing with CR0.WP to
prohibit CET && !WP as a legal combination.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ae37bc434ae67cf3d1b0d49bfd2dfde9ba7e04ba..28beacc45b993bcc186a48ed4358025a7b41354f 100644 (file)
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -976,11 +976,12 @@ const char *hvm_efer_valid(const struct vcpu *v, uint64_t value,
 unsigned long hvm_cr4_guest_valid_bits(const struct domain *d)
 {
     const struct cpuid_policy *p = d->arch.cpuid;
-    bool mce, vmxe;
+    bool mce, vmxe, cet;
 
     /* Logic broken out simply to aid readability below. */
     mce  = p->basic.mce || p->basic.mca;
     vmxe = p->basic.vmx && nestedhvm_enabled(d);
+    cet  = p->feat.cet_ss || p->feat.cet_ibt;
 
     return ((p->basic.vme     ? X86_CR4_VME | X86_CR4_PVI : 0) |
             (p->basic.tsc     ? X86_CR4_TSD               : 0) |
@@ -999,7 +1000,8 @@ unsigned long hvm_cr4_guest_valid_bits(const struct domain *d)
             (p->basic.xsave   ? X86_CR4_OSXSAVE           : 0) |
             (p->feat.smep     ? X86_CR4_SMEP              : 0) |
             (p->feat.smap     ? X86_CR4_SMAP              : 0) |
-            (p->feat.pku      ? X86_CR4_PKE               : 0));
+            (p->feat.pku      ? X86_CR4_PKE               : 0) |
+            (cet              ? X86_CR4_CET               : 0));
 }
 
 static int hvm_load_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
@@ -2289,6 +2291,12 @@ int hvm_set_cr0(unsigned long value, bool may_defer)
         }
     }
 
+    if ( !(value & X86_CR0_WP) && (v->arch.hvm.guest_cr[4] & X86_CR4_CET) )
+    {
+        gprintk(XENLOG_DEBUG, "Trying to clear WP with CET set\n");
+        return X86EMUL_EXCEPTION;
+    }
+
     if ( (value & X86_CR0_PG) && !(old_value & X86_CR0_PG) )
     {
         if ( v->arch.hvm.guest_efer & EFER_LME )
@@ -2444,6 +2452,12 @@ int hvm_set_cr4(unsigned long value, bool may_defer)
         }
     }
 
+    if ( (value & X86_CR4_CET) && !(v->arch.hvm.guest_cr[0] & X86_CR0_WP) )
+    {
+        gprintk(XENLOG_DEBUG, "Trying to set CET without WP\n");
+        return X86EMUL_EXCEPTION;
+    }
+
     old_cr = v->arch.hvm.guest_cr[4];
 
     if ( (value & X86_CR4_PCIDE) && !(old_cr & X86_CR4_PCIDE) &&