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.
Unified · Split
| @@ -116,6 +116,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/sev_migrate_tests · 115 unmodified lines | ||
| 116 | 116 | TEST_GEN_PROGS_x86_64 += x86_64/amx_test |
| 117 | 117 | TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test |
| 118 | 118 | TEST_GEN_PROGS_x86_64 += x86_64/triple_fault_event_test |
| 119 | +TEST_GEN_PROGS_x86_64 += x86_64/recalc_apic_map_test | |
| 119 | 120 | TEST_GEN_PROGS_x86_64 += access_tracking_perf_test |
| 120 | 121 | TEST_GEN_PROGS_x86_64 += demand_paging_test |
| 121 | 122 | TEST_GEN_PROGS_x86_64 += dirty_log_test |
| @@ -0,0 +1,74 @@ | ||
| 1 | +// SPDX-License-Identifier: GPL-2.0-only | |
| 2 | +/* | |
| 3 | + * Test edge cases and race conditions in kvm_recalculate_apic_map(). | |
| 4 | + */ | |
| 5 | + | |
| 6 | +#include <sys/ioctl.h> | |
| 7 | +#include <pthread.h> | |
| 8 | +#include <time.h> | |
| 9 | + | |
| 10 | +#include "processor.h" | |
| 11 | +#include "test_util.h" | |
| 12 | +#include "kvm_util.h" | |
| 13 | +#include "apic.h" | |
| 14 | + | |
| 15 | +#define TIMEOUT 5 /* seconds */ | |
| 16 | + | |
| 17 | +#define LAPIC_DISABLED 0 | |
| 18 | +#define LAPIC_X2APIC (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE) | |
| 19 | +#define MAX_XAPIC_ID 0xff | |
| 20 | + | |
| 21 | +static void *race(void *arg) | |
| 22 | +{ | |
| 23 | + struct kvm_lapic_state lapic = {}; | |
| 24 | + struct kvm_vcpu *vcpu = arg; | |
| 25 | + | |
| 26 | + while (1) { | |
| 27 | + /* Trigger kvm_recalculate_apic_map(). */ | |
| 28 | + vcpu_ioctl(vcpu, KVM_SET_LAPIC, &lapic); | |
| 29 | + pthread_testcancel(); | |
| 30 | + } | |
| 31 | + | |
| 32 | + return NULL; | |
| 33 | +} | |
| 34 | + | |
| 35 | +int main(void) | |
| 36 | +{ | |
| 37 | + struct kvm_vcpu *vcpus[KVM_MAX_VCPUS]; | |
| 38 | + struct kvm_vcpu *vcpuN; | |
| 39 | + struct kvm_vm *vm; | |
| 40 | + pthread_t thread; | |
| 41 | + time_t t; | |
| 42 | + int i; | |
| 43 | + | |
| 44 | + kvm_static_assert(KVM_MAX_VCPUS > MAX_XAPIC_ID); | |
| 45 | + | |
| 46 | + /* | |
| 47 | + * Create the max number of vCPUs supported by selftests so that KVM | |
| 48 | + * has decent amount of work to do when recalculating the map, i.e. to | |
| 49 | + * make the problematic window large enough to hit. | |
| 50 | + */ | |
| 51 | + vm = vm_create_with_vcpus(KVM_MAX_VCPUS, NULL, vcpus); | |
| 52 | + | |
| 53 | + /* | |
| 54 | + * Enable x2APIC on all vCPUs so that KVM doesn't bail from the recalc | |
| 55 | + * due to vCPUs having aliased xAPIC IDs (truncated to 8 bits). | |
| 56 | + */ | |
| 57 | + for (i = 0; i < KVM_MAX_VCPUS; i++) | |
| 58 | + vcpu_set_msr(vcpus[i], MSR_IA32_APICBASE, LAPIC_X2APIC); | |
| 59 | + | |
| 60 | + ASSERT_EQ(pthread_create(&thread, NULL, race, vcpus[0]), 0); | |
| 61 | + | |
| 62 | + vcpuN = vcpus[KVM_MAX_VCPUS - 1]; | |
| 63 | + for (t = time(NULL) + TIMEOUT; time(NULL) < t;) { | |
| 64 | + vcpu_set_msr(vcpuN, MSR_IA32_APICBASE, LAPIC_X2APIC); | |
| 65 | + vcpu_set_msr(vcpuN, MSR_IA32_APICBASE, LAPIC_DISABLED); | |
| 66 | + } | |
| 67 | + | |
| 68 | + ASSERT_EQ(pthread_cancel(thread), 0); | |
| 69 | + ASSERT_EQ(pthread_join(thread, NULL), 0); | |
| 70 | + | |
| 71 | + kvm_vm_free(vm); | |
| 72 | + | |
| 73 | + return 0; | |
| 74 | +} | |