From 9ed3c444ab8987c7b219173a2f7807e3f71e234e Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Tue, 4 May 2010 15:00:37 +0300 Subject: [PATCH] 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: Glauber Costa Signed-off-by: Avi Kivity --- arch/x86/kvm/x86.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index dff08e527ec7..54f73b6a006b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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)); -- 2.20.1