[PATCH v2 9/9] KVM: SVM: implement force_intercept_exceptions_mask

Maxim Levitsky
2021-04-01T18:02:24Z

Currently #TS interception is only done once.
Also exception interception is not enabled for SEV guests.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 2 +
arch/x86/kvm/svm/svm.c | 70 +++++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.h | 6 ++-
arch/x86/kvm/x86.c | 5 ++-
4 files changed, 80 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8c529ae9dbbe..d15ae64a2c4e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1574,6 +1574,8 @@ int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu);
void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr);
void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code);
void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr, unsigned long payload);
+void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,
+ u32 error_code, unsigned long payload);
void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr);
void kvm_requeue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code);
void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 2aa951bc470c..de7fd7922ec7 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -220,6 +220,8 @@ static const u32 msrpm_ranges[] = {0, 0xc0000000, 0xc0010000};
#define MSRS_RANGE_SIZE 2048
#define MSRS_IN_RANGE (MSRS_RANGE_SIZE * 8 / 2)

+static int svm_handle_invalid_exit(struct kvm_vcpu *vcpu, u64 exit_code);
+
u32 svm_msrpm_offset(u32 msr)
{
u32 offset;
@@ -1113,6 +1115,22 @@ static void svm_check_invpcid(struct vcpu_svm *svm)
}
}

+static void svm_init_force_exceptions_intercepts(struct vcpu_svm *svm)
+{
+ int exc;
+
+ svm->force_intercept_exceptions_mask = force_intercept_exceptions_mask;
+ for (exc = 0 ; exc < 32 ; exc++) {
+ if (!(svm->force_intercept_exceptions_mask & (1 << exc)))
+ continue;
+
+ /* Those are defined to have undefined behavior in the SVM spec */
+ if (exc != 2 && exc != 9)
+ continue;
+ set_exception_intercept(svm, exc);
+ }
+}
+
static void init_vmcb(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -1288,6 +1306,9 @@ static void init_vmcb(struct kvm_vcpu *vcpu)

enable_gif(svm);

+ if (!sev_es_guest(vcpu->kvm))
+ svm_init_force_exceptions_intercepts(svm);
+
}

static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
@@ -1913,6 +1934,17 @@ static int pf_interception(struct kvm_vcpu *vcpu)
u64 fault_address = svm->vmcb->control.exit_info_2;
u64 error_code = svm->vmcb->control.exit_info_1;

+ if ((svm->force_intercept_exceptions_mask & (1 << PF_VECTOR)))
+ if (npt_enabled && !vcpu->arch.apf.host_apf_flags) {
+ /* If the #PF was only intercepted for debug, inject
+ * it directly to the guest, since the kvm's mmu code
+ * is not ready to deal with such page faults.
+ */
+ kvm_queue_exception_e_p(vcpu, PF_VECTOR,
+ error_code, fault_address);
+ return 1;
+ }
+
return kvm_handle_page_fault(vcpu, error_code, fault_address,
static_cpu_has(X86_FEATURE_DECODEASSISTS) ?
svm->vmcb->control.insn_bytes : NULL,
@@ -1988,6 +2020,40 @@ static int ac_interception(struct kvm_vcpu *vcpu)
return 1;
}

+static int gen_exc_interception(struct kvm_vcpu *vcpu)
+{
+ /*
+ * Generic exception intercept handler which forwards a guest exception
+ * as-is to the guest.
+ * For exceptions that don't have a special intercept handler.
+ *
+ * Used only for 'force_intercept_exceptions_mask' KVM debug feature.
+ */
+ struct vcpu_svm *svm = to_svm(vcpu);
+ int exc = svm->vmcb->control.exit_code - SVM_EXIT_EXCP_BASE;
+
+ /* SVM doesn't provide us with an error code for the #DF */
+ u32 err_code = exc == DF_VECTOR ? 0 : svm->vmcb->control.exit_info_1;
+
+ if (!(svm->force_intercept_exceptions_mask & (1 << exc)))
+ return svm_handle_invalid_exit(vcpu, svm->vmcb->control.exit_code);
+
+ if (exc == TS_VECTOR) {
+ /*
+ * SVM doesn't provide us with an error code to be able to
+ * re-inject the #TS exception, so just disable its
+ * intercept, and let the guest re-execute the instruction.
+ */
+ vmcb_clr_intercept(&svm->vmcb01.ptr->control,
+ INTERCEPT_EXCEPTION_OFFSET + TS_VECTOR);
+ recalc_intercepts(svm);
+ } else if (x86_exception_has_error_code(exc))
+ kvm_queue_exception_e(vcpu, exc, err_code);
+ else
+ kvm_queue_exception(vcpu, exc);
+ return 1;
+}
+
static bool is_erratum_383(void)
{
int err, i;
@@ -3051,6 +3117,10 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[SVM_EXIT_WRITE_DR5] = dr_interception,
[SVM_EXIT_WRITE_DR6] = dr_interception,
[SVM_EXIT_WRITE_DR7] = dr_interception,
+
+ [SVM_EXIT_EXCP_BASE ...
+ SVM_EXIT_EXCP_BASE + 31] = gen_exc_interception,
+
[SVM_EXIT_EXCP_BASE + DB_VECTOR] = db_interception,
[SVM_EXIT_EXCP_BASE + BP_VECTOR] = bp_interception,
[SVM_EXIT_EXCP_BASE + UD_VECTOR] = ud_interception,
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 8e276c4fb33d..79d0aea87753 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -183,6 +183,7 @@ struct vcpu_svm {
bool ghcb_sa_free;

bool guest_state_loaded;
+ u32 force_intercept_exceptions_mask;
};

struct svm_cpu_data {
@@ -333,8 +334,11 @@ static inline void clr_exception_intercept(struct vcpu_svm *svm, u32 bit)
struct vmcb *vmcb = svm->vmcb01.ptr;

WARN_ON_ONCE(bit >= 32);
- vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);

+ if ((1 << bit) & svm->force_intercept_exceptions_mask)
+ return;
+
+ vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);
recalc_intercepts(svm);
}

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1a51031d64d8..ae57816fe6d9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -630,12 +630,13 @@ void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr,
}
EXPORT_SYMBOL_GPL(kvm_queue_exception_p);

-static void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,
- u32 error_code, unsigned long payload)
+void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,
+ u32 error_code, unsigned long payload)
{
kvm_multiple_exception(vcpu, nr, true, error_code,
true, payload, false);
}
+EXPORT_SYMBOL_GPL(kvm_queue_exception_e_p);

int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err)
{
--
2.26.2