[PATCH 5.18 0032/1095] KVM: x86: Split kvm_is_valid_cr4() and export only the non-vendor bits

Greg Kroah-Hartman
2022-08-15T20:13:56Z

From: Sean Christopherson <seanjc@google.com>

commit c33f6f2228fe8517e38941a508e9f905f99ecba9 upstream.

Split the common x86 parts of kvm_is_valid_cr4(), i.e. the reserved bits
checks, into a separate helper, __kvm_is_valid_cr4(), and export only the
inner helper to vendor code in order to prevent nested VMX from calling
back into vmx_is_valid_cr4() via kvm_is_valid_cr4().

On SVM, this is a nop as SVM doesn't place any additional restrictions on
CR4.

On VMX, this is also currently a nop, but only because nested VMX is
missing checks on reserved CR4 bits for nested VM-Enter. That bug will
be fixed in a future patch, and could simply use kvm_is_valid_cr4() as-is,
but nVMX has _another_ bug where VMXON emulation doesn't enforce VMX's
restrictions on CR0/CR4. The cleanest and most intuitive way to fix the
VMXON bug is to use nested_host_cr{0,4}_valid(). If the CR4 variant
routes through kvm_is_valid_cr4(), using nested_host_cr4_valid() won't do
the right thing for the VMXON case as vmx_is_valid_cr4() enforces VMX's
restrictions if and only if the vCPU is post-VMXON.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220607213604.3346000-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/svm/nested.c | 3 ++-
arch/x86/kvm/vmx/vmx.c | 4 ++--
arch/x86/kvm/x86.c | 12 +++++++++---
arch/x86/kvm/x86.h | 2 +-
4 files changed, 14 insertions(+), 7 deletions(-)

--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -292,7 +292,8 @@ static bool __nested_vmcb_check_save(str
return false;
}

- if (CC(!kvm_is_valid_cr4(vcpu, save->cr4)))
+ /* Note, SVM doesn't have any additional restrictions on CR4. */
+ if (CC(!__kvm_is_valid_cr4(vcpu, save->cr4)))
return false;

if (CC(!kvm_valid_efer(vcpu, save->efer)))
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3230,8 +3230,8 @@ static bool vmx_is_valid_cr4(struct kvm_
{
/*
* We operate under the default treatment of SMM, so VMX cannot be
- * enabled under SMM. Note, whether or not VMXE is allowed at all is
- * handled by kvm_is_valid_cr4().
+ * enabled under SMM. Note, whether or not VMXE is allowed at all,
+ * i.e. is a reserved bit, is handled by common x86 code.
*/
if ((cr4 & X86_CR4_VMXE) && is_smm(vcpu))
return false;
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1066,7 +1066,7 @@ int kvm_emulate_xsetbv(struct kvm_vcpu *
}
EXPORT_SYMBOL_GPL(kvm_emulate_xsetbv);

-bool kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+bool __kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
if (cr4 & cr4_reserved_bits)
return false;
@@ -1074,9 +1074,15 @@ bool kvm_is_valid_cr4(struct kvm_vcpu *v
if (cr4 & vcpu->arch.cr4_guest_rsvd_bits)
return false;

- return static_call(kvm_x86_is_valid_cr4)(vcpu, cr4);
+ return true;
+}
+EXPORT_SYMBOL_GPL(__kvm_is_valid_cr4);
+
+static bool kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+{
+ return __kvm_is_valid_cr4(vcpu, cr4) &&
+ static_call(kvm_x86_is_valid_cr4)(vcpu, cr4);
}
-EXPORT_SYMBOL_GPL(kvm_is_valid_cr4);

void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned long cr4)
{
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -407,7 +407,7 @@ static inline void kvm_machine_check(voi
void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
int kvm_spec_ctrl_test_value(u64 value);
-bool kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
+bool __kvm_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
struct x86_exception *e);
int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva);