[PATCH stable-5.2 0/3] KVM: x86: FPU and nested VMX guest reset fixes

[PATCH stable-5.2 0/3] KVM: x86: FPU and nested VMX guest reset fixes

[Vitaly Kuznetsov]

Few patches were recently marked for stable@ but commits are not
backportable as-is and require a few tweaks. Here is 5.2 stable backport.

[PATCHes 2/3 of the series apply as-is, I have them here for completeness]

Jan Kiszka (1):
  KVM: nVMX: Clear pending KVM_REQ_GET_VMCS12_PAGES when leaving nested

Paolo Bonzini (2):
  KVM: nVMX: do not use dangling shadow VMCS after guest reset
  Revert "kvm: x86: Use task structs fpu field for user"

 arch/x86/include/asm/kvm_host.h |  7 ++++---
 arch/x86/kvm/vmx/nested.c       | 10 +++++++++-
 arch/x86/kvm/x86.c              |  4 ++--
 3 files changed, 15 insertions(+), 6 deletions(-)

-- 
2.20.1

[PATCH stable-5.2 1/3] KVM: nVMX: do not use dangling shadow VMCS after guest reset

[Vitaly Kuznetsov]

From: Paolo Bonzini <pbonzini@redhat.com>

[ Upstream commit 88dddc11a8d6b09201b4db9d255b3394d9bc9e57 ]

If a KVM guest is reset while running a nested guest, free_nested will
disable the shadow VMCS execution control in the vmcs01.  However,
on the next KVM_RUN vmx_vcpu_run would nevertheless try to sync
the VMCS12 to the shadow VMCS which has since been freed.

This causes a vmptrld of a NULL pointer on my machime, but Jan reports
the host to hang altogether.  Let's see how much this trivial patch fixes.

Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 46af3a5e9209..b72d6aec4e90 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -184,6 +184,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx)
 {
 	vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL, SECONDARY_EXEC_SHADOW_VMCS);
 	vmcs_write64(VMCS_LINK_POINTER, -1ull);
+	vmx->nested.need_vmcs12_sync = false;
 }
 
 static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
@@ -1321,6 +1322,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx)
 	u64 field_value;
 	struct vmcs *shadow_vmcs = vmx->vmcs01.shadow_vmcs;
 
+	if (WARN_ON(!shadow_vmcs))
+		return;
+
 	preempt_disable();
 
 	vmcs_load(shadow_vmcs);
@@ -1359,6 +1363,9 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx)
 	u64 field_value = 0;
 	struct vmcs *shadow_vmcs = vmx->vmcs01.shadow_vmcs;
 
+	if (WARN_ON(!shadow_vmcs))
+		return;
+
 	vmcs_load(shadow_vmcs);
 
 	for (q = 0; q < ARRAY_SIZE(fields); q++) {
@@ -4304,7 +4311,6 @@ static inline void nested_release_vmcs12(struct kvm_vcpu *vcpu)
 		/* copy to memory all shadowed fields in case
 		   they were modified */
 		copy_shadow_to_vmcs12(vmx);
-		vmx->nested.need_vmcs12_sync = false;
 		vmx_disable_shadow_vmcs(vmx);
 	}
 	vmx->nested.posted_intr_nv = -1;
-- 
2.20.1

[PATCH stable-5.2 2/3] KVM: nVMX: Clear pending KVM_REQ_GET_VMCS12_PAGES when leaving nested

[Vitaly Kuznetsov]

From: Jan Kiszka <jan.kiszka@siemens.com>

[ Upstream commit cf64527bb33f6cec2ed50f89182fc4688d0056b6 ]

Letting this pend may cause nested_get_vmcs12_pages to run against an
invalid state, corrupting the effective vmcs of L1.

This was triggerable in QEMU after a guest corruption in L2, followed by
a L1 reset.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Cc: stable@vger.kernel.org
Fixes: 7f7f1ba33cf2 ("KVM: x86: do not load vmcs12 pages while still in SMM")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index b72d6aec4e90..df6e26894e25 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -210,6 +210,8 @@ static void free_nested(struct kvm_vcpu *vcpu)
 	if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon)
 		return;
 
+	kvm_clear_request(KVM_REQ_GET_VMCS12_PAGES, vcpu);
+
 	vmx->nested.vmxon = false;
 	vmx->nested.smm.vmxon = false;
 	free_vpid(vmx->nested.vpid02);
-- 
2.20.1

[PATCH stable-5.2 3/3] Revert "kvm: x86: Use task structs fpu field for user"

[Vitaly Kuznetsov]

From: Paolo Bonzini <pbonzini@redhat.com>

[ Upstream commit ec269475cba7bcdd1eb8fdf8e87f4c6c81a376fe ]

This reverts commit 240c35a3783ab9b3a0afaba0dde7291295680a6b
("kvm: x86: Use task structs fpu field for user", 2018-11-06).
The commit is broken and causes QEMU's FPU state to be destroyed
when KVM_RUN is preempted.

Fixes: 240c35a3783a ("kvm: x86: Use task structs fpu field for user")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/include/asm/kvm_host.h | 7 ++++---
 arch/x86/kvm/x86.c              | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 26d1eb83f72a..08f46951c430 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -607,15 +607,16 @@ struct kvm_vcpu_arch {
 
 	/*
 	 * QEMU userspace and the guest each have their own FPU state.
-	 * In vcpu_run, we switch between the user, maintained in the
-	 * task_struct struct, and guest FPU contexts. While running a VCPU,
-	 * the VCPU thread will have the guest FPU context.
+	 * In vcpu_run, we switch between the user and guest FPU contexts.
+	 * While running a VCPU, the VCPU thread will have the guest FPU
+	 * context.
 	 *
 	 * Note that while the PKRU state lives inside the fpu registers,
 	 * it is switched out separately at VMENTER and VMEXIT time. The
 	 * "guest_fpu" state here contains the guest FPU context, with the
 	 * host PRKU bits.
 	 */
+	struct fpu user_fpu;
 	struct fpu *guest_fpu;
 
 	u64 xcr0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fafd81d2c9ea..a4eceb0b5dde 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8219,7 +8219,7 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
 {
 	fpregs_lock();
 
-	copy_fpregs_to_fpstate(&current->thread.fpu);
+	copy_fpregs_to_fpstate(&vcpu->arch.user_fpu);
 	/* PKRU is separately restored in kvm_x86_ops->run.  */
 	__copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,
 				~XFEATURE_MASK_PKRU);
@@ -8236,7 +8236,7 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
 	fpregs_lock();
 
 	copy_fpregs_to_fpstate(vcpu->arch.guest_fpu);
-	copy_kernel_to_fpregs(&current->thread.fpu.state);
+	copy_kernel_to_fpregs(&vcpu->arch.user_fpu.state);
 
 	fpregs_mark_activate();
 	fpregs_unlock();
-- 
2.20.1

Re: [PATCH stable-5.2 0/3] KVM: x86: FPU and nested VMX guest reset fixes

[Paolo Bonzini]

On 25/07/19 14:04, Vitaly Kuznetsov wrote:
> Few patches were recently marked for stable@ but commits are not
> backportable as-is and require a few tweaks. Here is 5.2 stable backport.
> 
> [PATCHes 2/3 of the series apply as-is, I have them here for completeness]
> 
> Jan Kiszka (1):
>   KVM: nVMX: Clear pending KVM_REQ_GET_VMCS12_PAGES when leaving nested
> 
> Paolo Bonzini (2):
>   KVM: nVMX: do not use dangling shadow VMCS after guest reset
>   Revert "kvm: x86: Use task structs fpu field for user"
> 
>  arch/x86/include/asm/kvm_host.h |  7 ++++---
>  arch/x86/kvm/vmx/nested.c       | 10 +++++++++-
>  arch/x86/kvm/x86.c              |  4 ++--
>  3 files changed, 15 insertions(+), 6 deletions(-)
> 

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Re: [PATCH stable-5.2 0/3] KVM: x86: FPU and nested VMX guest reset fixes

[Greg KH]

On Thu, Jul 25, 2019 at 02:04:33PM +0200, Vitaly Kuznetsov wrote:
> Few patches were recently marked for stable@ but commits are not
> backportable as-is and require a few tweaks. Here is 5.2 stable backport.
> 
> [PATCHes 2/3 of the series apply as-is, I have them here for completeness]
> 
> Jan Kiszka (1):
>   KVM: nVMX: Clear pending KVM_REQ_GET_VMCS12_PAGES when leaving nested
> 
> Paolo Bonzini (2):
>   KVM: nVMX: do not use dangling shadow VMCS after guest reset
>   Revert "kvm: x86: Use task structs fpu field for user"

All now applied, thanks!

greg k-h