Commit 9ed3c444 authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: Fix wallclock version writing race 



Wallclock writing uses an unprotected global variable to hold the version;
this can cause one guest to interfere with another if both write their
wallclock at the same time.

Acked-by: default avatarGlauber Costa <glommer@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 8facbbff

arch/x86/kvm/x86.c

+10 −2
Original line number Diff line number Diff line
@@ -754,14 +754,22 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data) 


static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)

{

	static int version;

	int version;

	int r;

	struct pvclock_wall_clock wc;

	struct timespec boot;



	if (!wall_clock)

		return;



	version++;

	r = kvm_read_guest(kvm, wall_clock, &version, sizeof(version));

	if (r)

		return;



	if (version & 1)

		++version;  /* first time write, random junk */



	++version;



	kvm_write_guest(kvm, wall_clock, &version, sizeof(version));