[kernel,v5,4/6] KVM: SVM/SEV/SEV-ES: Rework intercepts
Commit Message
Currently SVM setup is done sequentially in
init_vmcb() -> sev_init_vmcb() -> sev_es_init_vmcb()
and tries keeping SVM/SEV/SEV-ES bits separated. One of the exceptions
is DR intercepts which is for SEV-ES before sev_es_init_vmcb() runs.
Move the SEV-ES intercept setup to sev_es_init_vmcb(). From now on
set_dr_intercepts()/clr_dr_intercepts() handle SVM/SEV only.
No functional change intended.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
Reviewed-by: Santosh Shukla <santosh.shukla@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---
Changes:
v5:
* updated the comments
* removed sev_es_guest() checks from set_dr_intercepts()/clr_dr_intercepts()
* removed remaining intercepts from clr_dr_intercepts()
---
arch/x86/kvm/svm/sev.c | 11 ++++++
arch/x86/kvm/svm/svm.c | 37 ++++++++------------
2 files changed, 25 insertions(+), 23 deletions(-)
Comments
On Tue, Apr 11, 2023, Alexey Kardashevskiy wrote:
> Currently SVM setup is done sequentially in
> init_vmcb() -> sev_init_vmcb() -> sev_es_init_vmcb()
> and tries keeping SVM/SEV/SEV-ES bits separated. One of the exceptions
> is DR intercepts which is for SEV-ES before sev_es_init_vmcb() runs.
>
> Move the SEV-ES intercept setup to sev_es_init_vmcb(). From now on
> set_dr_intercepts()/clr_dr_intercepts() handle SVM/SEV only.
>
> No functional change intended.
>
> Suggested-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Alexey Kardashevskiy <aik@amd.com>
> Reviewed-by: Santosh Shukla <santosh.shukla@amd.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> Changes:
> v5:
> * updated the comments
> * removed sev_es_guest() checks from set_dr_intercepts()/clr_dr_intercepts()
> * removed remaining intercepts from clr_dr_intercepts()
> ---
> arch/x86/kvm/svm/sev.c | 11 ++++++
> arch/x86/kvm/svm/svm.c | 37 ++++++++------------
> 2 files changed, 25 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index b4365622222b..f0885250252d 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2946,6 +2946,7 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
>
> static void sev_es_init_vmcb(struct vcpu_svm *svm)
> {
> + struct vmcb *vmcb = svm->vmcb01.ptr;
> struct kvm_vcpu *vcpu = &svm->vcpu;
>
> svm->vmcb->control.nested_ctl |= SVM_NESTED_CTL_SEV_ES_ENABLE;
> @@ -2974,6 +2975,16 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
> svm_set_intercept(svm, TRAP_CR4_WRITE);
> svm_set_intercept(svm, TRAP_CR8_WRITE);
>
> + /*
> + * DR7 access must remain intercepted for an SEV-ES guest to disallow
> + * the guest kernel enable debugging as otherwise a VM writing to DR7
> + * from the #DB handler may trigger infinite loop of #DB's.
This is wrong. The attack isn't writing DR7 in the #DB handler, it's setting up
a #DB on memory that's needed to vector a #DB, e.g. the stack, so that the _CPU_
itself gets stuck in an infinite #DB loop[*]. The guest software handler putting
itself into an infinite loop is a non-issue because it can be interrupted.
[*] https://bugzilla.redhat.com/show_bug.cgi?id=1278496
> + */
> + vmcb->control.intercepts[INTERCEPT_DR] = 0;
> + vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
> + vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
> + recalc_intercepts(svm);
@@ -2946,6 +2946,7 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
static void sev_es_init_vmcb(struct vcpu_svm *svm)
{
+ struct vmcb *vmcb = svm->vmcb01.ptr;
struct kvm_vcpu *vcpu = &svm->vcpu;
svm->vmcb->control.nested_ctl |= SVM_NESTED_CTL_SEV_ES_ENABLE;
@@ -2974,6 +2975,16 @@ static void sev_es_init_vmcb(struct vcpu_svm *svm)
svm_set_intercept(svm, TRAP_CR4_WRITE);
svm_set_intercept(svm, TRAP_CR8_WRITE);
+ /*
+ * DR7 access must remain intercepted for an SEV-ES guest to disallow
+ * the guest kernel enable debugging as otherwise a VM writing to DR7
+ * from the #DB handler may trigger infinite loop of #DB's.
+ */
+ vmcb->control.intercepts[INTERCEPT_DR] = 0;
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
+ recalc_intercepts(svm);
+
/* Can't intercept XSETBV, HV can't modify XCR0 directly */
svm_clr_intercept(svm, INTERCEPT_XSETBV);
@@ -691,23 +691,20 @@ static void set_dr_intercepts(struct vcpu_svm *svm)
{
struct vmcb *vmcb = svm->vmcb01.ptr;
- if (!sev_es_guest(svm->vcpu.kvm)) {
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_WRITE);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_WRITE);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_WRITE);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_WRITE);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_WRITE);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_WRITE);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE);
- }
-
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_READ);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_WRITE);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_WRITE);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_WRITE);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_WRITE);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_WRITE);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_WRITE);
+ vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE);
vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
@@ -720,12 +717,6 @@ static void clr_dr_intercepts(struct vcpu_svm *svm)
vmcb->control.intercepts[INTERCEPT_DR] = 0;
- /* DR7 access must remain intercepted for an SEV-ES guest */
- if (sev_es_guest(svm->vcpu.kvm)) {
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
- vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
- }
-
recalc_intercepts(svm);
}