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 <glommer@redhat.com> Signed-off-by: Avi Kivity <avi@redhat.com>
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@ -754,14 +754,22 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
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static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
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static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
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{
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{
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static int version;
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int version;
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int r;
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struct pvclock_wall_clock wc;
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struct pvclock_wall_clock wc;
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struct timespec boot;
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struct timespec boot;
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if (!wall_clock)
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if (!wall_clock)
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return;
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return;
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version++;
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r = kvm_read_guest(kvm, wall_clock, &version, sizeof(version));
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if (r)
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return;
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if (version & 1)
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++version; /* first time write, random junk */
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++version;
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kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
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kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
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