2020-09-23 21:55:44

by Sean Christopherson

Subject: [PATCH] KVM: x86: Reset MMU context if guest toggles CR4.SMAP or CR4.PKE

Reset the MMU context during kvm_set_cr4() if SMAP or PKE is toggled.
Recent commits to (correctly) not reload PDPTRs when SMAP/PKE are
toggled inadvertantly skipped the MMU context reset due to the mask
of bits that triggers PDPTR loads also being used to trigger MMU context
resets.

Fixes: 427890aff855 ("kvm: x86: Toggling CR4.SMAP does not load PDPTEs in PAE mode")
Fixes: cb957adb4ea4 ("kvm: x86: Toggling CR4.PKE does not load PDPTEs in PAE mode")
Cc: Jim Mattson <[email protected]>
Cc: Peter Shier <[email protected]>
Cc: Oliver Upton <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/x86.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 17f4995e80a7..fd0da41bc149 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -977,6 +977,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
unsigned long old_cr4 = kvm_read_cr4(vcpu);
unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
X86_CR4_SMEP;
+ unsigned long mmu_role_bits = pdptr_bits | X86_CR4_SMAP | X86_CR4_PKE;

if (kvm_valid_cr4(vcpu, cr4))
return 1;
@@ -1004,7 +1005,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
if (kvm_x86_ops.set_cr4(vcpu, cr4))
return 1;

- if (((cr4 ^ old_cr4) & pdptr_bits) ||
+ if (((cr4 ^ old_cr4) & mmu_role_bits) ||
(!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
kvm_mmu_reset_context(vcpu);

--
2.28.0

2020-09-24 21:49:44

by Jim Mattson

Subject: Re: [PATCH] KVM: x86: Reset MMU context if guest toggles CR4.SMAP or CR4.PKE

On Wed, Sep 23, 2020 at 2:54 PM Sean Christopherson
<[email protected]> wrote:
>
> Reset the MMU context during kvm_set_cr4() if SMAP or PKE is toggled.
> Recent commits to (correctly) not reload PDPTRs when SMAP/PKE are
> toggled inadvertantly skipped the MMU context reset due to the mask
> of bits that triggers PDPTR loads also being used to trigger MMU context
> resets.
>
> Fixes: 427890aff855 ("kvm: x86: Toggling CR4.SMAP does not load PDPTEs in PAE mode")
> Fixes: cb957adb4ea4 ("kvm: x86: Toggling CR4.PKE does not load PDPTEs in PAE mode")
> Cc: Jim Mattson <[email protected]>
> Cc: Peter Shier <[email protected]>
> Cc: Oliver Upton <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>

Thanks for the fix!

Reviewed-by: Jim Mattson <[email protected]>

2020-09-25 13:01:28

by Paolo Bonzini

Subject: Re: [PATCH] KVM: x86: Reset MMU context if guest toggles CR4.SMAP or CR4.PKE

On 23/09/20 23:53, Sean Christopherson wrote:
> Reset the MMU context during kvm_set_cr4() if SMAP or PKE is toggled.
> Recent commits to (correctly) not reload PDPTRs when SMAP/PKE are
> toggled inadvertantly skipped the MMU context reset due to the mask
> of bits that triggers PDPTR loads also being used to trigger MMU context
> resets.
>
> Fixes: 427890aff855 ("kvm: x86: Toggling CR4.SMAP does not load PDPTEs in PAE mode")
> Fixes: cb957adb4ea4 ("kvm: x86: Toggling CR4.PKE does not load PDPTEs in PAE mode")
> Cc: Jim Mattson <[email protected]>
> Cc: Peter Shier <[email protected]>
> Cc: Oliver Upton <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/x86.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 17f4995e80a7..fd0da41bc149 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -977,6 +977,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> unsigned long old_cr4 = kvm_read_cr4(vcpu);
> unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
> X86_CR4_SMEP;
> + unsigned long mmu_role_bits = pdptr_bits | X86_CR4_SMAP | X86_CR4_PKE;
>
> if (kvm_valid_cr4(vcpu, cr4))
> return 1;
> @@ -1004,7 +1005,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> if (kvm_x86_ops.set_cr4(vcpu, cr4))
> return 1;
>
> - if (((cr4 ^ old_cr4) & pdptr_bits) ||
> + if (((cr4 ^ old_cr4) & mmu_role_bits) ||
> (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
> kvm_mmu_reset_context(vcpu);
>
>

Queued, thanks.

Paolo