Re: [PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs

[Yang Weijiang]

On Thu, Oct 17, 2019 at 12:58:11PM -0700, Sean Christopherson wrote:
> On Wed, Oct 02, 2019 at 01:57:50PM -0700, Jim Mattson wrote:
> > On Thu, Sep 26, 2019 at 7:17 PM Yang Weijiang  
> > wrote:
> > >
> > > There're two different places storing Guest CET states, the states
> > > managed with XSAVES/XRSTORS, as restored/saved
> > > in previous patch, can be read/write directly from/to the MSRs.
> > > For those stored in VMCS fields, they're access via vmcs_read/
> > > vmcs_write.
> > >
> > > Signed-off-by: Yang Weijiang 
> > > ---
> > >  arch/x86/kvm/vmx/vmx.c | 83 ++
> > >  1 file changed, 83 insertions(+)
> > >
> > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > > index 44913e4ab558..5265db7cd2af 100644
> > > --- a/arch/x86/kvm/vmx/vmx.c
> > > +++ b/arch/x86/kvm/vmx/vmx.c
> > > @@ -1671,6 +1671,49 @@ static int vmx_get_msr_feature(struct 
> > > kvm_msr_entry *msr)
> > > return 0;
> > >  }
> > >
> > > +static int check_cet_msr(struct kvm_vcpu *vcpu, struct msr_data 
> > > *msr_info)
> > 
> > I'd suggest changing return type to bool, since you are essentially
> > returning true or false.
> 
> I'd also be more explicit in the name, e.g. is_valid_cet_msr().
Sure, thank you two.

Re: [PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs

[Sean Christopherson]

On Wed, Oct 02, 2019 at 01:57:50PM -0700, Jim Mattson wrote:
> On Thu, Sep 26, 2019 at 7:17 PM Yang Weijiang  wrote:
> >
> > There're two different places storing Guest CET states, the states
> > managed with XSAVES/XRSTORS, as restored/saved
> > in previous patch, can be read/write directly from/to the MSRs.
> > For those stored in VMCS fields, they're access via vmcs_read/
> > vmcs_write.
> >
> > Signed-off-by: Yang Weijiang 
> > ---
> >  arch/x86/kvm/vmx/vmx.c | 83 ++
> >  1 file changed, 83 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 44913e4ab558..5265db7cd2af 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -1671,6 +1671,49 @@ static int vmx_get_msr_feature(struct kvm_msr_entry 
> > *msr)
> > return 0;
> >  }
> >
> > +static int check_cet_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 
> I'd suggest changing return type to bool, since you are essentially
> returning true or false.

I'd also be more explicit in the name, e.g. is_valid_cet_msr().

Re: [PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs

[Yang Weijiang]

On Wed, Oct 02, 2019 at 01:57:50PM -0700, Jim Mattson wrote:
> On Thu, Sep 26, 2019 at 7:17 PM Yang Weijiang  wrote:
> >
> > There're two different places storing Guest CET states, the states
> > managed with XSAVES/XRSTORS, as restored/saved
> > in previous patch, can be read/write directly from/to the MSRs.
> > For those stored in VMCS fields, they're access via vmcs_read/
> > vmcs_write.
> >
> > Signed-off-by: Yang Weijiang 
> > ---
> >  arch/x86/kvm/vmx/vmx.c | 83 ++
> >  1 file changed, 83 insertions(+)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 44913e4ab558..5265db7cd2af 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -1671,6 +1671,49 @@ static int vmx_get_msr_feature(struct kvm_msr_entry 
> > *msr)
> > return 0;
> >  }
> >
> > +static int check_cet_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> 
> I'd suggest changing return type to bool, since you are essentially
> returning true or false.
>
Sure, will change it.

> > +{
> > +   u64 kvm_xss = kvm_supported_xss();
> > +
> > +   switch (msr_info->index) {
> > +   case MSR_IA32_PL0_SSP ... MSR_IA32_PL2_SSP:
> > +   if (!(kvm_xss | XFEATURE_MASK_CET_KERNEL))
> '|' should be '&'
Oops, thanks for the capture!

> > +   return 1;
> > +   if (!msr_info->host_initiated &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> > +   return 1;
> > +   break;
> > +   case MSR_IA32_PL3_SSP:
> > +   if (!(kvm_xss | XFEATURE_MASK_CET_USER))
> '|' should be '&'
> > +   return 1;
> > +   if (!msr_info->host_initiated &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> > +   return 1;
> > +   break;
> > +   case MSR_IA32_U_CET:
> > +   if (!(kvm_xss | XFEATURE_MASK_CET_USER))
> '|' should be '&'
> > +   return 1;
> > +   if (!msr_info->host_initiated &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> > +   return 1;
> > +   break;
> > +   case MSR_IA32_S_CET:
> > +   if (!msr_info->host_initiated &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> > +   return 1;
> > +   break;
> > +   case MSR_IA32_INT_SSP_TAB:
> > +   if (!msr_info->host_initiated &&
> > +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> > +   return 1;
> > +   break;
> > +   default:
> > +   return 1;
> > +   }
> > +   return 0;
> > +}
> >  /*
> >   * Reads an msr value (of 'msr_index') into 'pdata'.
> >   * Returns 0 on success, non-0 otherwise.
> > @@ -1788,6 +1831,26 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct 
> > msr_data *msr_info)
> > else
> > msr_info->data = vmx->pt_desc.guest.addr_a[index / 
> > 2];
> > break;
> > +   case MSR_IA32_S_CET:
> > +   if (check_cet_msr(vcpu, msr_info))
> > +   return 1;
> > +   msr_info->data = vmcs_readl(GUEST_S_CET);
> Have we ensured that this VMCS field exists?
> > +   break;
> > +   case MSR_IA32_INT_SSP_TAB:
> > +   if (check_cet_msr(vcpu, msr_info))
> > +   return 1;
> > +   msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
> Have we ensured that this VMCS field exists?
If host kernel sets correct info, we can make sure here.

> > +   break;
> > +   case MSR_IA32_U_CET:
> Can this be lumped together with MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP, below?
Unfortunately, this MSR is not adjacent to below MSRs.

> > +   if (check_cet_msr(vcpu, msr_info))
> > +   return 1;
> > +   rdmsrl(MSR_IA32_U_CET, msr_info->data);
> > +   break;
> > +   case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
> > +   if (check_cet_msr(vcpu, msr_info))
> > +   return 1;
> > +   rdmsrl(msr_info->index, msr_info->data);
> > +   break;
> > case MSR_TSC_AUX:
> > if (!msr_info->host_initiated &&
> > !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> > @@ -2039,6 +2102,26 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct 
> > msr_data *msr_info)
> > else
> > vmx->pt_desc.guest.addr_a[index / 2] = data;
> > break;
> > +   case MSR_IA32_S_CET:
> > +   if (check_cet_msr(vcpu, msr_info))
> > +   return 1;
> Bits 9:6 must be zero.
> > +   

Re: [PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs

[Jim Mattson]

On Thu, Sep 26, 2019 at 7:17 PM Yang Weijiang  wrote:
>
> There're two different places storing Guest CET states, the states
> managed with XSAVES/XRSTORS, as restored/saved
> in previous patch, can be read/write directly from/to the MSRs.
> For those stored in VMCS fields, they're access via vmcs_read/
> vmcs_write.
>
> Signed-off-by: Yang Weijiang 
> ---
>  arch/x86/kvm/vmx/vmx.c | 83 ++
>  1 file changed, 83 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 44913e4ab558..5265db7cd2af 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1671,6 +1671,49 @@ static int vmx_get_msr_feature(struct kvm_msr_entry 
> *msr)
> return 0;
>  }
>
> +static int check_cet_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

I'd suggest changing return type to bool, since you are essentially
returning true or false.

> +{
> +   u64 kvm_xss = kvm_supported_xss();
> +
> +   switch (msr_info->index) {
> +   case MSR_IA32_PL0_SSP ... MSR_IA32_PL2_SSP:
> +   if (!(kvm_xss | XFEATURE_MASK_CET_KERNEL))
'|' should be '&'
> +   return 1;
> +   if (!msr_info->host_initiated &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> +   return 1;
> +   break;
> +   case MSR_IA32_PL3_SSP:
> +   if (!(kvm_xss | XFEATURE_MASK_CET_USER))
'|' should be '&'
> +   return 1;
> +   if (!msr_info->host_initiated &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> +   return 1;
> +   break;
> +   case MSR_IA32_U_CET:
> +   if (!(kvm_xss | XFEATURE_MASK_CET_USER))
'|' should be '&'
> +   return 1;
> +   if (!msr_info->host_initiated &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> +   return 1;
> +   break;
> +   case MSR_IA32_S_CET:
> +   if (!msr_info->host_initiated &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> +   return 1;
> +   break;
> +   case MSR_IA32_INT_SSP_TAB:
> +   if (!msr_info->host_initiated &&
> +   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> +   return 1;
> +   break;
> +   default:
> +   return 1;
> +   }
> +   return 0;
> +}
>  /*
>   * Reads an msr value (of 'msr_index') into 'pdata'.
>   * Returns 0 on success, non-0 otherwise.
> @@ -1788,6 +1831,26 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct 
> msr_data *msr_info)
> else
> msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
> break;
> +   case MSR_IA32_S_CET:
> +   if (check_cet_msr(vcpu, msr_info))
> +   return 1;
> +   msr_info->data = vmcs_readl(GUEST_S_CET);
Have we ensured that this VMCS field exists?
> +   break;
> +   case MSR_IA32_INT_SSP_TAB:
> +   if (check_cet_msr(vcpu, msr_info))
> +   return 1;
> +   msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
Have we ensured that this VMCS field exists?
> +   break;
> +   case MSR_IA32_U_CET:
Can this be lumped together with MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP, below?
> +   if (check_cet_msr(vcpu, msr_info))
> +   return 1;
> +   rdmsrl(MSR_IA32_U_CET, msr_info->data);
> +   break;
> +   case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
> +   if (check_cet_msr(vcpu, msr_info))
> +   return 1;
> +   rdmsrl(msr_info->index, msr_info->data);
> +   break;
> case MSR_TSC_AUX:
> if (!msr_info->host_initiated &&
> !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> @@ -2039,6 +2102,26 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct 
> msr_data *msr_info)
> else
> vmx->pt_desc.guest.addr_a[index / 2] = data;
> break;
> +   case MSR_IA32_S_CET:
> +   if (check_cet_msr(vcpu, msr_info))
> +   return 1;
Bits 9:6 must be zero.
> +   vmcs_writel(GUEST_S_CET, data);
Have we ensured that this VMCS field exists?
> +   break;
> +   case MSR_IA32_INT_SSP_TAB:
> +   if (check_cet_msr(vcpu, msr_info))
> +   return 1;
Must be canonical. vCPU must support longmode.
> +   vmcs_writel(GUEST_INTR_SSP_TABLE, data);
Have we ensured that this VMCS field exists?
> +   break;
> +   case MSR_IA32_U_CET:
> +   if 

[PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs

[Yang Weijiang]

There're two different places storing Guest CET states, the states
managed with XSAVES/XRSTORS, as restored/saved
in previous patch, can be read/write directly from/to the MSRs.
For those stored in VMCS fields, they're access via vmcs_read/
vmcs_write.

Signed-off-by: Yang Weijiang 
---
 arch/x86/kvm/vmx/vmx.c | 83 ++
 1 file changed, 83 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 44913e4ab558..5265db7cd2af 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1671,6 +1671,49 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
return 0;
 }
 
+static int check_cet_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+{
+   u64 kvm_xss = kvm_supported_xss();
+
+   switch (msr_info->index) {
+   case MSR_IA32_PL0_SSP ... MSR_IA32_PL2_SSP:
+   if (!(kvm_xss | XFEATURE_MASK_CET_KERNEL))
+   return 1;
+   if (!msr_info->host_initiated &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
+   return 1;
+   break;
+   case MSR_IA32_PL3_SSP:
+   if (!(kvm_xss | XFEATURE_MASK_CET_USER))
+   return 1;
+   if (!msr_info->host_initiated &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
+   return 1;
+   break;
+   case MSR_IA32_U_CET:
+   if (!(kvm_xss | XFEATURE_MASK_CET_USER))
+   return 1;
+   if (!msr_info->host_initiated &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
+   return 1;
+   break;
+   case MSR_IA32_S_CET:
+   if (!msr_info->host_initiated &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
+   return 1;
+   break;
+   case MSR_IA32_INT_SSP_TAB:
+   if (!msr_info->host_initiated &&
+   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
+   return 1;
+   break;
+   default:
+   return 1;
+   }
+   return 0;
+}
 /*
  * Reads an msr value (of 'msr_index') into 'pdata'.
  * Returns 0 on success, non-0 otherwise.
@@ -1788,6 +1831,26 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct 
msr_data *msr_info)
else
msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
break;
+   case MSR_IA32_S_CET:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   msr_info->data = vmcs_readl(GUEST_S_CET);
+   break;
+   case MSR_IA32_INT_SSP_TAB:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
+   break;
+   case MSR_IA32_U_CET:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   rdmsrl(MSR_IA32_U_CET, msr_info->data);
+   break;
+   case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   rdmsrl(msr_info->index, msr_info->data);
+   break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
@@ -2039,6 +2102,26 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct 
msr_data *msr_info)
else
vmx->pt_desc.guest.addr_a[index / 2] = data;
break;
+   case MSR_IA32_S_CET:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   vmcs_writel(GUEST_S_CET, data);
+   break;
+   case MSR_IA32_INT_SSP_TAB:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   vmcs_writel(GUEST_INTR_SSP_TABLE, data);
+   break;
+   case MSR_IA32_U_CET:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   wrmsrl(MSR_IA32_U_CET, data);
+   break;
+   case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+   if (check_cet_msr(vcpu, msr_info))
+   return 1;
+   wrmsrl(msr_info->index, data);
+   break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
-- 
2.17.2