Messages in this thread | | | Date | Mon, 16 Jun 2014 13:09:56 +0200 | From | Paolo Bonzini <> | Subject | Re: [PATCH 6/6] KVM: x86: check DR6/7 high-bits are clear only on long-mode |
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Il 16/06/2014 12:33, Nadav Amit ha scritto: >> >> Do you get this if the input register has bit 31 set? > No. To be frank, the scenario may be considered a bit synthetic: the > guest assigns a value to a general-purpose register in 64-bit mode, > setting the high 32-bits to some non-zero value. Then, later, in 32-bit > mode, the guest performs MOV DR instruction. In between the two > assignments, the general purpose register is unmodified, so the high > 32-bits of the general purpose registers are still set. > > Note that this scenario does not occur when MOV DR is emulated, but when > handle_dr() is called. In this case, the entire 64-bits of the general > purpose register used for MOV DR are read, regardless to the execution > mode of the guest.
I wonder if the same bug happens elsewhere. For example, kvm_emulate_hypercall doesn't look at CS.L/CS.DB, which is really a corner case but arguably also a bug. kvm_hv_hypercall instead does it right.
Perhaps we need a variant of kvm_register_read that (on 64-bit hosts) checks EFER/CS.L/CS.DB and masks the returned value accordingly. You could call it kvm_register_readl.
Paolo
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