| Date | Thu, 01 Jul 2010 10:35:41 -0700 | From | Greg KH <> | Subject | [patch 155/164] KVM: Fix wallclock version writing race |
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2.6.33-stable review patch. If anyone has any objections, please let me know.
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From: Avi Kivity <avi@redhat.com>
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 <glommer@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> (cherry picked from commit 9ed3c444ab8987c7b219173a2f7807e3f71e234e) --- arch/x86/kvm/x86.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -641,14 +641,22 @@ static int do_set_msr(struct kvm_vcpu *v 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));
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