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KVM: selftests: Add test for race in kvm_recalculate_apic_map()

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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>
This commit is contained in:
Michal Luczaj 2023-06-02 16:32:50 -07:00 committed by Sean Christopherson
parent 4364b28798
commit 47d2804bc9
2 changed files with 75 additions and 0 deletions
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1
tools/testing/selftests/kvm/Makefile
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@ -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

74
tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c Normal file
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@ -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;
}