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.

Michal Luczaj committed 3 years ago

Commit 47d28041 parent 4364b282 files · +75 −0Browse files

Unified · Split

2 files

tools/testing/selftests/kvm/Makefile +1 −0
tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c +74 −0

tools/testing/selftests/kvm/Makefile+1−0

@@ -116,6 +116,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/sev_migrate_tests · 115 unmodified lines
116	TEST_GEN_PROGS_x86_64 += x86_64/amx_test	116	TEST_GEN_PROGS_x86_64 += x86_64/amx_test
117	TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test	117	TEST_GEN_PROGS_x86_64 += x86_64/max_vcpuid_cap_test
118	TEST_GEN_PROGS_x86_64 += x86_64/triple_fault_event_test	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	TEST_GEN_PROGS_x86_64 += access_tracking_perf_test	120	TEST_GEN_PROGS_x86_64 += access_tracking_perf_test
120	TEST_GEN_PROGS_x86_64 += demand_paging_test	121	TEST_GEN_PROGS_x86_64 += demand_paging_test
121	TEST_GEN_PROGS_x86_64 += dirty_log_test	122	TEST_GEN_PROGS_x86_64 += dirty_log_test

tools/testing/selftests/kvm/x86_64/recalc_apic_map_test.c+74−0

@@ -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	}