| Message ID | 1448443299-9375-1-git-send-email-haozhong.zhang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Haozhong Zhang <haozhong.zhang@intel.com> writes: > This patch removes the vpid check when emulating nested invvpid > instruction of type all-contexts invalidation. The existing code is > incorrect because: > (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate > Translations Based on VPID", invvpid instruction does not check > vpid in the invvpid descriptor when its type is all-contexts > invalidation. But iirc isn't vpid=0 reserved for root mode ? I think we don't want L1 hypervisor to be able do a invvpid(0). > (2) According to the same document, invvpid of type all-contexts > invalidation does not require there is an active VMCS, so/and > get_vmcs12() in the existing code may result in a NULL-pointer > dereference. In practice, it can crash both KVM itself and L1 > hypervisors that use invvpid (e.g. Xen). If that is the case, then just check if it's null and return without doing anything. > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com> > --- > arch/x86/kvm/vmx.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 87acc52..af823a3 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) > > switch (type) { > case VMX_VPID_EXTENT_ALL_CONTEXT: > - if (get_vmcs12(vcpu)->virtual_processor_id == 0) { > - nested_vmx_failValid(vcpu, > - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); > - return 1; > - } > __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02); > nested_vmx_succeed(vcpu); > break; I also noticed a BUG() here in the default. It might be a good idea to replace it with a WARN. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 11/25/15 10:45, Bandan Das wrote: > Haozhong Zhang <haozhong.zhang@intel.com> writes: > > > This patch removes the vpid check when emulating nested invvpid > > instruction of type all-contexts invalidation. The existing code is > > incorrect because: > > (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate > > Translations Based on VPID", invvpid instruction does not check > > vpid in the invvpid descriptor when its type is all-contexts > > invalidation. > > But iirc isn't vpid=0 reserved for root mode ? Yes, > I think we don't want > L1 hypervisor to be able do a invvpid(0). but the invvpid emulated here is doing the all-contexts invalidation that does not use the given vpid and "invalidates all mappings tagged with all VPIDs except VPID 0000H" (from Intel SDM). > > > (2) According to the same document, invvpid of type all-contexts > > invalidation does not require there is an active VMCS, so/and > > get_vmcs12() in the existing code may result in a NULL-pointer > > dereference. In practice, it can crash both KVM itself and L1 > > hypervisors that use invvpid (e.g. Xen). > > If that is the case, then just check if it's null and return without > doing anything. (according to Intel SDM) invvpid of type all-contexts invalidation should not trigger a valid vmx fail if vpid in the current VMCS is 0. However, this check and its following operation do change this semantics in nested VMX, so it should be completely removed. > > > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com> > > --- > > arch/x86/kvm/vmx.c | 5 ----- > > 1 file changed, 5 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > > index 87acc52..af823a3 100644 > > --- a/arch/x86/kvm/vmx.c > > +++ b/arch/x86/kvm/vmx.c > > @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) > > > > switch (type) { > > case VMX_VPID_EXTENT_ALL_CONTEXT: > > - if (get_vmcs12(vcpu)->virtual_processor_id == 0) { > > - nested_vmx_failValid(vcpu, > > - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); > > - return 1; > > - } > > __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02); > > nested_vmx_succeed(vcpu); > > break; > > I also noticed a BUG() here in the default. It might be a good idea to replace > it with a WARN. Or, in nested_vmx_setup_ctls_msrs(): if (enable_vpid) - vmx->nested.nested_vmx_vpid_caps = VMX_VPID_INVVPID_BIT | - VMX_VPID_EXTENT_GLOBAL_CONTEXT_BIT; + vmx->nested.nested_vmx_vpid_caps = VMX_VPID_EXTENT_GLOBAL_CONTEXT_BIT; because the current handle_invvpid() only handles all-contexts invalidation. Haozhong -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 25/11/2015 16:45, Bandan Das wrote: > Haozhong Zhang <haozhong.zhang@intel.com> writes: > >> This patch removes the vpid check when emulating nested invvpid >> instruction of type all-contexts invalidation. The existing code is >> incorrect because: >> (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate >> Translations Based on VPID", invvpid instruction does not check >> vpid in the invvpid descriptor when its type is all-contexts >> invalidation. > > But iirc isn't vpid=0 reserved for root mode ? I think we don't want > L1 hypervisor to be able do a invvpid(0). The instruction simply "invalidates all mappings tagged with all non-zero VPIDs", which in our case is all L0 mappings tagged with vpid02. Paolo >> (2) According to the same document, invvpid of type all-contexts >> invalidation does not require there is an active VMCS, so/and >> get_vmcs12() in the existing code may result in a NULL-pointer >> dereference. In practice, it can crash both KVM itself and L1 >> hypervisors that use invvpid (e.g. Xen). > > If that is the case, then just check if it's null and return without > doing anything. > >> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com> >> --- >> arch/x86/kvm/vmx.c | 5 ----- >> 1 file changed, 5 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index 87acc52..af823a3 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) >> >> switch (type) { >> case VMX_VPID_EXTENT_ALL_CONTEXT: >> - if (get_vmcs12(vcpu)->virtual_processor_id == 0) { >> - nested_vmx_failValid(vcpu, >> - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); >> - return 1; >> - } >> __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02); >> nested_vmx_succeed(vcpu); >> break; > > I also noticed a BUG() here in the default. It might be a good idea to replace > it with a WARN. > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Haozhong Zhang <haozhong.zhang@intel.com> writes: > On 11/25/15 10:45, Bandan Das wrote: >> Haozhong Zhang <haozhong.zhang@intel.com> writes: >> >> > This patch removes the vpid check when emulating nested invvpid >> > instruction of type all-contexts invalidation. The existing code is >> > incorrect because: >> > (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate >> > Translations Based on VPID", invvpid instruction does not check >> > vpid in the invvpid descriptor when its type is all-contexts >> > invalidation. >> >> But iirc isn't vpid=0 reserved for root mode ? > Yes, > >> I think we don't want >> L1 hypervisor to be able do a invvpid(0). > > but the invvpid emulated here is doing the all-contexts invalidation that > does not use the given vpid and "invalidates all mappings tagged with all > VPIDs except VPID 0000H" (from Intel SDM). Actually, vpid_sync_context will always try single invalidation first and I was concerned that we will end up calling vpid_sync_context(0). But that will not happen since nested.vpid02 is always allocated a vpid. So... we are good :) >> >> > (2) According to the same document, invvpid of type all-contexts >> > invalidation does not require there is an active VMCS, so/and >> > get_vmcs12() in the existing code may result in a NULL-pointer >> > dereference. In practice, it can crash both KVM itself and L1 >> > hypervisors that use invvpid (e.g. Xen). >> >> If that is the case, then just check if it's null and return without >> doing anything. > > (according to Intel SDM) invvpid of type all-contexts invalidation > should not trigger a valid vmx fail if vpid in the current VMCS is 0. No, I meant just skip instruction and return but I doubt if there's any overhead of flushing mappings that don't exist in the first place. Anyway, better to do as the spec says. > However, this check and its following operation do change this semantics > in nested VMX, so it should be completely removed. > >> >> > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com> >> > --- >> > arch/x86/kvm/vmx.c | 5 ----- >> > 1 file changed, 5 deletions(-) >> > >> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> > index 87acc52..af823a3 100644 >> > --- a/arch/x86/kvm/vmx.c >> > +++ b/arch/x86/kvm/vmx.c >> > @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) >> > >> > switch (type) { >> > case VMX_VPID_EXTENT_ALL_CONTEXT: >> > - if (get_vmcs12(vcpu)->virtual_processor_id == 0) { >> > - nested_vmx_failValid(vcpu, >> > - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); >> > - return 1; >> > - } >> > __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02); >> > nested_vmx_succeed(vcpu); >> > break; >> >> I also noticed a BUG() here in the default. It might be a good idea to replace >> it with a WARN. > > Or, in nested_vmx_setup_ctls_msrs(): > > if (enable_vpid) > - vmx->nested.nested_vmx_vpid_caps = VMX_VPID_INVVPID_BIT | > - VMX_VPID_EXTENT_GLOBAL_CONTEXT_BIT; > + vmx->nested.nested_vmx_vpid_caps = VMX_VPID_EXTENT_GLOBAL_CONTEXT_BIT; > > because the current handle_invvpid() only handles all-contexts invalidation. > > Haozhong > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 87acc52..af823a3 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -7394,11 +7394,6 @@ static int handle_invvpid(struct kvm_vcpu *vcpu) switch (type) { case VMX_VPID_EXTENT_ALL_CONTEXT: - if (get_vmcs12(vcpu)->virtual_processor_id == 0) { - nested_vmx_failValid(vcpu, - VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID); - return 1; - } __vmx_flush_tlb(vcpu, to_vmx(vcpu)->nested.vpid02); nested_vmx_succeed(vcpu); break;
This patch removes the vpid check when emulating nested invvpid instruction of type all-contexts invalidation. The existing code is incorrect because: (1) According to Intel SDM Vol 3, Section "INVVPID - Invalidate Translations Based on VPID", invvpid instruction does not check vpid in the invvpid descriptor when its type is all-contexts invalidation. (2) According to the same document, invvpid of type all-contexts invalidation does not require there is an active VMCS, so/and get_vmcs12() in the existing code may result in a NULL-pointer dereference. In practice, it can crash both KVM itself and L1 hypervisors that use invvpid (e.g. Xen). Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com> --- arch/x86/kvm/vmx.c | 5 ----- 1 file changed, 5 deletions(-)