ptp: Fix ptp_kvm_getcrosststamp issue for x86 ptp_kvm

hv_clock is preallocated to have only HVC_BOOT_ARRAY_SIZE (64) elements;
if the PTP_SYS_OFFSET_PRECISE ioctl is executed on vCPUs whose index is
64 of higher, retrieving the struct pvclock_vcpu_time_info pointer with
"src = &hv_clock[cpu].pvti" will result in an out-of-bounds access and
a wild pointer.  Change it to "this_cpu_pvti()" which is guaranteed to
be valid.

Fixes: 95a3d445 ("Switch kvmclock data to a PER_CPU variable")
Signed-off-by: Zelin Deng <zelin.deng@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
Message-Id: <1632892429-101194-3-git-send-email-zelin.deng@linux.alibaba.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

drivers/ptp/ptp_kvm_x86.c

@@ -15,8 +15,6 @@
 #include <linux/ptp_clock_kernel.h>
 #include <linux/ptp_kvm.h>
 
-struct pvclock_vsyscall_time_info *hv_clock;
-
 static phys_addr_t clock_pair_gpa;
 static struct kvm_clock_pairing clock_pair;
 
@@ -28,8 +26,7 @@ int kvm_arch_ptp_init(void)
 		return -ENODEV;
 
 	clock_pair_gpa = slow_virt_to_phys(&clock_pair);
-	hv_clock = pvclock_get_pvti_cpu0_va();
-	if (!hv_clock)
+	if (!pvclock_get_pvti_cpu0_va())
 		return -ENODEV;
 
 	ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING, clock_pair_gpa,
@@ -64,10 +61,8 @@ int kvm_arch_ptp_get_crosststamp(u64 *cycle, struct timespec64 *tspec,
 	struct pvclock_vcpu_time_info *src;
 	unsigned int version;
 	long ret;
-	int cpu;
 
-	cpu = smp_processor_id();
-	src = &hv_clock[cpu].pvti;
+	src = this_cpu_pvti();
 
 	do {
 		/*