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authorMichal Luczaj <mhal@rbox.co>2023-06-02 16:32:50 -0700
committerSean Christopherson <seanjc@google.com>2023-06-02 17:21:06 -0700
commit47d2804bc99ca873470df17c20737b28225a320d (patch)
tree7dd9a1f8b6e62f3a3759a87adb81c2e655466237
parent4364b287982bd05bfafa461c80650c732001974b (diff)
KVM: selftests: Add test for race in kvm_recalculate_apic_map()
Keep switching between LAPIC_MODE_X2APIC and LAPIC_MODE_DISABLED during APIC map construction to hunt for TOCTOU bugs in KVM. KVM's optimized map recalc makes multiple passes over the list of vCPUs, and the calculations ignore vCPU's whose APIC is hardware-disabled, i.e. there's a window where toggling LAPIC_MODE_DISABLED is quite interesting. Signed-off-by: Michal Luczaj <mhal@rbox.co> Co-developed-by: Sean Christopherson <seanjc@google.com> Link: https://lore.kernel.org/r/20230602233250.1014316-4-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
-rw-r--r--tools/testing/selftests/kvm/Makefile1
-rw-r--r--tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c74
2 files changed, 75 insertions, 0 deletions
diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 7a5ff646e7e7..4761b768b773 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -116,6 +116,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/sev_migrate_tests
TEST_GEN_PROGS_x86_64 += x86_64/amx_test
TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test
TEST_GEN_PROGS_x86_64 += x86_64/triple_fault_event_test
+TEST_GEN_PROGS_x86_64 += x86_64/recalc_apic_map_test
TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
TEST_GEN_PROGS_x86_64 += demand_paging_test
TEST_GEN_PROGS_x86_64 += dirty_log_test
diff --git a/tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c b/tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c
new file mode 100644
index 000000000000..4c416ebe7d66
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Test edge cases and race conditions in kvm_recalculate_apic_map().
+ */
+
+#include <sys/ioctl.h>
+#include <pthread.h>
+#include <time.h>
+
+#include "processor.h"
+#include "test_util.h"
+#include "kvm_util.h"
+#include "apic.h"
+
+#define TIMEOUT 5 /* seconds */
+
+#define LAPIC_DISABLED 0
+#define LAPIC_X2APIC (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE)
+#define MAX_XAPIC_ID 0xff
+
+static void *race(void *arg)
+{
+ struct kvm_lapic_state lapic = {};
+ struct kvm_vcpu *vcpu = arg;
+
+ while (1) {
+ /* Trigger kvm_recalculate_apic_map(). */
+ vcpu_ioctl(vcpu, KVM_SET_LAPIC, &lapic);
+ pthread_testcancel();
+ }
+
+ return NULL;
+}
+
+int main(void)
+{
+ struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+ struct kvm_vcpu *vcpuN;
+ struct kvm_vm *vm;
+ pthread_t thread;
+ time_t t;
+ int i;
+
+ kvm_static_assert(KVM_MAX_VCPUS > MAX_XAPIC_ID);
+
+ /*
+ * Create the max number of vCPUs supported by selftests so that KVM
+ * has decent amount of work to do when recalculating the map, i.e. to
+ * make the problematic window large enough to hit.
+ */
+ vm = vm_create_with_vcpus(KVM_MAX_VCPUS, NULL, vcpus);
+
+ /*
+ * Enable x2APIC on all vCPUs so that KVM doesn't bail from the recalc
+ * due to vCPUs having aliased xAPIC IDs (truncated to 8 bits).
+ */
+ for (i = 0; i < KVM_MAX_VCPUS; i++)
+ vcpu_set_msr(vcpus[i], MSR_IA32_APICBASE, LAPIC_X2APIC);
+
+ ASSERT_EQ(pthread_create(&thread, NULL, race, vcpus[0]), 0);
+
+ vcpuN = vcpus[KVM_MAX_VCPUS - 1];
+ for (t = time(NULL) + TIMEOUT; time(NULL) < t;) {
+ vcpu_set_msr(vcpuN, MSR_IA32_APICBASE, LAPIC_X2APIC);
+ vcpu_set_msr(vcpuN, MSR_IA32_APICBASE, LAPIC_DISABLED);
+ }
+
+ ASSERT_EQ(pthread_cancel(thread), 0);
+ ASSERT_EQ(pthread_join(thread, NULL), 0);
+
+ kvm_vm_free(vm);
+
+ return 0;
+}