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Message-Id: <20221027161849.2989332-16-pbonzini@redhat.com>
Date: Thu, 27 Oct 2022 12:18:48 -0400
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: mhal@...x.co, seanjc@...gle.com
Subject: [PATCH 15/16] KVM: selftests: Add tests in xen_shinfo_test to detect lock races
From: Michal Luczaj <mhal@...x.co>
Tests for races between shinfo_cache (de)activation and hypercall+ioctl()
processing. KVM has had bugs where activating the shared info cache
multiple times and/or with concurrent users results in lock corruption,
NULL pointer dereferences, and other fun.
For the timer injection testcase (#22), re-arm the timer until the IRQ
is successfully injected. If the timer expires while the shared info
is deactivated (invalid), KVM will drop the event.
Signed-off-by: Michal Luczaj <mhal@...x.co>
Co-developed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20221013211234.1318131-16-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
.../selftests/kvm/x86_64/xen_shinfo_test.c | 140 ++++++++++++++++++
1 file changed, 140 insertions(+)
diff --git a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
index 8a5cb800f50e..caa3f5ab9e10 100644
--- a/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xen_shinfo_test.c
@@ -15,9 +15,13 @@
#include <time.h>
#include <sched.h>
#include <signal.h>
+#include <pthread.h>
#include <sys/eventfd.h>
+/* Defined in include/linux/kvm_types.h */
+#define GPA_INVALID (~(ulong)0)
+
#define SHINFO_REGION_GVA 0xc0000000ULL
#define SHINFO_REGION_GPA 0xc0000000ULL
#define SHINFO_REGION_SLOT 10
@@ -44,6 +48,8 @@
#define MIN_STEAL_TIME 50000
+#define SHINFO_RACE_TIMEOUT 2 /* seconds */
+
#define __HYPERVISOR_set_timer_op 15
#define __HYPERVISOR_sched_op 29
#define __HYPERVISOR_event_channel_op 32
@@ -148,6 +154,7 @@ static void guest_wait_for_irq(void)
static void guest_code(void)
{
struct vcpu_runstate_info *rs = (void *)RUNSTATE_VADDR;
+ int i;
__asm__ __volatile__(
"sti\n"
@@ -325,6 +332,49 @@ static void guest_code(void)
guest_wait_for_irq();
GUEST_SYNC(21);
+ /* Racing host ioctls */
+
+ guest_wait_for_irq();
+
+ GUEST_SYNC(22);
+ /* Racing vmcall against host ioctl */
+
+ ports[0] = 0;
+
+ p = (struct sched_poll) {
+ .ports = ports,
+ .nr_ports = 1,
+ .timeout = 0
+ };
+
+wait_for_timer:
+ /*
+ * Poll for a timer wake event while the worker thread is mucking with
+ * the shared info. KVM XEN drops timer IRQs if the shared info is
+ * invalid when the timer expires. Arbitrarily poll 100 times before
+ * giving up and asking the VMM to re-arm the timer. 100 polls should
+ * consume enough time to beat on KVM without taking too long if the
+ * timer IRQ is dropped due to an invalid event channel.
+ */
+ for (i = 0; i < 100 && !guest_saw_irq; i++)
+ asm volatile("vmcall"
+ : "=a" (rax)
+ : "a" (__HYPERVISOR_sched_op),
+ "D" (SCHEDOP_poll),
+ "S" (&p)
+ : "memory");
+
+ /*
+ * Re-send the timer IRQ if it was (likely) dropped due to the timer
+ * expiring while the event channel was invalid.
+ */
+ if (!guest_saw_irq) {
+ GUEST_SYNC(23);
+ goto wait_for_timer;
+ }
+ guest_saw_irq = false;
+
+ GUEST_SYNC(24);
}
static int cmp_timespec(struct timespec *a, struct timespec *b)
@@ -352,11 +402,36 @@ static void handle_alrm(int sig)
TEST_FAIL("IRQ delivery timed out");
}
+static void *juggle_shinfo_state(void *arg)
+{
+ struct kvm_vm *vm = (struct kvm_vm *)arg;
+
+ struct kvm_xen_hvm_attr cache_init = {
+ .type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
+ .u.shared_info.gfn = SHINFO_REGION_GPA / PAGE_SIZE
+ };
+
+ struct kvm_xen_hvm_attr cache_destroy = {
+ .type = KVM_XEN_ATTR_TYPE_SHARED_INFO,
+ .u.shared_info.gfn = GPA_INVALID
+ };
+
+ for (;;) {
+ __vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_init);
+ __vm_ioctl(vm, KVM_XEN_HVM_SET_ATTR, &cache_destroy);
+ pthread_testcancel();
+ };
+
+ return NULL;
+}
+
int main(int argc, char *argv[])
{
struct timespec min_ts, max_ts, vm_ts;
struct kvm_vm *vm;
+ pthread_t thread;
bool verbose;
+ int ret;
verbose = argc > 1 && (!strncmp(argv[1], "-v", 3) ||
!strncmp(argv[1], "--verbose", 10));
@@ -785,6 +860,71 @@ int main(int argc, char *argv[])
case 21:
TEST_ASSERT(!evtchn_irq_expected,
"Expected event channel IRQ but it didn't happen");
+ alarm(0);
+
+ if (verbose)
+ printf("Testing shinfo lock corruption (KVM_XEN_HVM_EVTCHN_SEND)\n");
+
+ ret = pthread_create(&thread, NULL, &juggle_shinfo_state, (void *)vm);
+ TEST_ASSERT(ret == 0, "pthread_create() failed: %s", strerror(ret));
+
+ struct kvm_irq_routing_xen_evtchn uxe = {
+ .port = 1,
+ .vcpu = vcpu->id,
+ .priority = KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL
+ };
+
+ evtchn_irq_expected = true;
+ for (time_t t = time(NULL) + SHINFO_RACE_TIMEOUT; time(NULL) < t;)
+ __vm_ioctl(vm, KVM_XEN_HVM_EVTCHN_SEND, &uxe);
+ break;
+
+ case 22:
+ TEST_ASSERT(!evtchn_irq_expected,
+ "Expected event channel IRQ but it didn't happen");
+
+ if (verbose)
+ printf("Testing shinfo lock corruption (SCHEDOP_poll)\n");
+
+ shinfo->evtchn_pending[0] = 1;
+
+ evtchn_irq_expected = true;
+ tmr.u.timer.expires_ns = rs->state_entry_time +
+ SHINFO_RACE_TIMEOUT * 1000000000ULL;
+ vcpu_ioctl(vcpu, KVM_XEN_VCPU_SET_ATTR, &tmr);
+ break;
+
+ case 23:
+ /*
+ * Optional and possibly repeated sync point.
+ * Injecting the timer IRQ may fail if the
+ * shinfo is invalid when the timer expires.
+ * If the timer has expired but the IRQ hasn't
+ * been delivered, rearm the timer and retry.
+ */
+ vcpu_ioctl(vcpu, KVM_XEN_VCPU_GET_ATTR, &tmr);
+
+ /* Resume the guest if the timer is still pending. */
+ if (tmr.u.timer.expires_ns)
+ break;
+
+ /* All done if the IRQ was delivered. */
+ if (!evtchn_irq_expected)
+ break;
+
+ tmr.u.timer.expires_ns = rs->state_entry_time +
+ SHINFO_RACE_TIMEOUT * 1000000000ULL;
+ vcpu_ioctl(vcpu, KVM_XEN_VCPU_SET_ATTR, &tmr);
+ break;
+ case 24:
+ TEST_ASSERT(!evtchn_irq_expected,
+ "Expected event channel IRQ but it didn't happen");
+
+ ret = pthread_cancel(thread);
+ TEST_ASSERT(ret == 0, "pthread_cancel() failed: %s", strerror(ret));
+
+ ret = pthread_join(thread, 0);
+ TEST_ASSERT(ret == 0, "pthread_join() failed: %s", strerror(ret));
goto done;
case 0x20:
--
2.31.1
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