Messages in this thread | | | Date | Mon, 16 Jun 2014 13:33:27 +0300 | From | Nadav Amit <> | Subject | Re: [PATCH 6/6] KVM: x86: check DR6/7 high-bits are clear only on long-mode |
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On 6/16/14, 1:17 PM, Paolo Bonzini wrote: > Il 15/06/2014 15:13, Nadav Amit ha scritto: >> From: Nadav Amit <nadav.amit@gmail.com> >> >> When the guest sets DR6 and DR7, KVM asserts the high 32-bits are >> clear, and >> otherwise injects a #GP exception. This exception should only be >> injected only >> if running in long-mode. >> >> Signed-off-by: Nadav Amit <namit@cs.technion.ac.il> >> --- >> arch/x86/kvm/x86.c | 13 +++++++++++-- >> 1 file changed, 11 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 57eac30..71fe841 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -756,6 +756,15 @@ static void kvm_update_dr7(struct kvm_vcpu *vcpu) >> vcpu->arch.switch_db_regs |= KVM_DEBUGREG_BP_ENABLED; >> } >> >> +static bool is_64_bit_mode(struct kvm_vcpu *vcpu) >> +{ >> + int cs_db, cs_l; >> + if (!is_long_mode(vcpu)) >> + return false; >> + kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l); >> + return cs_l; >> +} >> + >> static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long >> val) >> { >> switch (dr) { >> @@ -769,7 +778,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int >> dr, unsigned long val) >> return 1; /* #UD */ >> /* fall through */ >> case 6: >> - if (val & 0xffffffff00000000ULL) >> + if ((val & 0xffffffff00000000ULL) && is_64_bit_mode(vcpu)) >> return -1; /* #GP */ >> vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1; >> kvm_update_dr6(vcpu); >> @@ -779,7 +788,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int >> dr, unsigned long val) >> return 1; /* #UD */ >> /* fall through */ >> default: /* 7 */ >> - if (val & 0xffffffff00000000ULL) >> + if ((val & 0xffffffff00000000ULL) && is_64_bit_mode(vcpu)) >> return -1; /* #GP */ >> vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1; >> kvm_update_dr7(vcpu); >> > > 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.
Nadav
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