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 4f23e34f628b..0f1378789bd0 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -194,6 +194,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx) { secondary_exec_controls_clearbit(vmx, SECONDARY_EXEC_SHADOW_VMCS); vmcs_write64(VMCS_LINK_POINTER, -1ull); + vmx->nested.need_vmcs12_to_shadow_sync = false; }
static inline void nested_release_evmcs(struct kvm_vcpu *vcpu) @@ -1341,6 +1342,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) unsigned long val; int i;
+ if (WARN_ON(!shadow_vmcs)) + return; + preempt_disable();
vmcs_load(shadow_vmcs); @@ -1373,6 +1377,9 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) unsigned long val; int i, q;
+ if (WARN_ON(!shadow_vmcs)) + return; + vmcs_load(shadow_vmcs);
for (q = 0; q < ARRAY_SIZE(fields); q++) { @@ -4436,7 +4443,6 @@ 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_to_shadow_sync = false; vmx_disable_shadow_vmcs(vmx); } vmx->nested.posted_intr_nv = -1;
On 20 Jul 2019, at 0:39, Paolo Bonzini pbonzini@redhat.com wrote:
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
1) Are we sure we prefer WARN_ON() instead of WARN_ON_ONCE()? 2) Should we also check for WARN_ON(!vmcs12)? As free_nested() also kfree(vmx->nested.cached_vmcs12). In fact, because free_nested() don’t put NULL in cached_vmcs12 after kfree() it, I wonder if we shouldn’t create a separate patch that does: (a) Modify free_nested() to put NULL in cached_vmcs12 after kfree(). (b) Put BUG_ON(!cached_vmcs12) in get_vmcs12() before returning value.
-Liran
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 4f23e34f628b..0f1378789bd0 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -194,6 +194,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx) { secondary_exec_controls_clearbit(vmx, SECONDARY_EXEC_SHADOW_VMCS); vmcs_write64(VMCS_LINK_POINTER, -1ull);
- vmx->nested.need_vmcs12_to_shadow_sync = false;
}
static inline void nested_release_evmcs(struct kvm_vcpu *vcpu) @@ -1341,6 +1342,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) unsigned long val; int i;
if (WARN_ON(!shadow_vmcs))
return;preempt_disable();
vmcs_load(shadow_vmcs);
@@ -1373,6 +1377,9 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) unsigned long val; int i, q;
if (WARN_ON(!shadow_vmcs))
return;vmcs_load(shadow_vmcs);
for (q = 0; q < ARRAY_SIZE(fields); q++) {
@@ -4436,7 +4443,6 @@ 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_to_shadow_sync = false;-- 1.8.3.1
On 20/07/19 00:06, Liran Alon wrote:
On 20 Jul 2019, at 0:39, Paolo Bonzini pbonzini@redhat.com wrote:
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
- Are we sure we prefer WARN_ON() instead of WARN_ON_ONCE()?
I don't think you can get it to be called in a loop, the calls are generally guarded by ifs.
- Should we also check for WARN_ON(!vmcs12)? As free_nested() also kfree(vmx->nested.cached_vmcs12).
Well, it doesn't NULL it but it does NULL shadow_vmcs so the extra warning wouldn't add much.
In fact, because free_nested() don’t put NULL in cached_vmcs12 after kfree() it, I wonder if we shouldn’t create a separate patch that does: (a) Modify free_nested() to put NULL in cached_vmcs12 after kfree(). (b) Put BUG_ON(!cached_vmcs12) in get_vmcs12() before returning value.
This is useful but a separate improvement (and not a bugfix, I want this patch to be small so it applies to older trees).
Paolo
-Liran
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 4f23e34f628b..0f1378789bd0 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -194,6 +194,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx) { secondary_exec_controls_clearbit(vmx, SECONDARY_EXEC_SHADOW_VMCS); vmcs_write64(VMCS_LINK_POINTER, -1ull);
- vmx->nested.need_vmcs12_to_shadow_sync = false;
}
static inline void nested_release_evmcs(struct kvm_vcpu *vcpu) @@ -1341,6 +1342,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) unsigned long val; int i;
if (WARN_ON(!shadow_vmcs))
return;preempt_disable();
vmcs_load(shadow_vmcs);
@@ -1373,6 +1377,9 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) unsigned long val; int i, q;
if (WARN_ON(!shadow_vmcs))
return;vmcs_load(shadow_vmcs);
for (q = 0; q < ARRAY_SIZE(fields); q++) {
@@ -4436,7 +4443,6 @@ 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_to_shadow_sync = false;-- 1.8.3.1
On 20 Jul 2019, at 1:21, Paolo Bonzini pbonzini@redhat.com wrote:
On 20/07/19 00:06, Liran Alon wrote:
On 20 Jul 2019, at 0:39, Paolo Bonzini pbonzini@redhat.com wrote:
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
- Are we sure we prefer WARN_ON() instead of WARN_ON_ONCE()?
I don't think you can get it to be called in a loop, the calls are generally guarded by ifs.
- Should we also check for WARN_ON(!vmcs12)? As free_nested() also kfree(vmx->nested.cached_vmcs12).
Well, it doesn't NULL it but it does NULL shadow_vmcs so the extra warning wouldn't add much.
In fact, because free_nested() don’t put NULL in cached_vmcs12 after kfree() it, I wonder if we shouldn’t create a separate patch that does: (a) Modify free_nested() to put NULL in cached_vmcs12 after kfree(). (b) Put BUG_ON(!cached_vmcs12) in get_vmcs12() before returning value.
This is useful but a separate improvement (and not a bugfix, I want this patch to be small so it applies to older trees).
Paolo
ACK on all the above. :) Reviewed-by: Liran Alon liran.alon@oracle.com
-Liran
-Liran
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 4f23e34f628b..0f1378789bd0 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -194,6 +194,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx) { secondary_exec_controls_clearbit(vmx, SECONDARY_EXEC_SHADOW_VMCS); vmcs_write64(VMCS_LINK_POINTER, -1ull);
- vmx->nested.need_vmcs12_to_shadow_sync = false;
}
static inline void nested_release_evmcs(struct kvm_vcpu *vcpu) @@ -1341,6 +1342,9 @@ static void copy_shadow_to_vmcs12(struct vcpu_vmx *vmx) unsigned long val; int i;
if (WARN_ON(!shadow_vmcs))
return;preempt_disable();
vmcs_load(shadow_vmcs);
@@ -1373,6 +1377,9 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx) unsigned long val; int i, q;
if (WARN_ON(!shadow_vmcs))
return;vmcs_load(shadow_vmcs);
for (q = 0; q < ARRAY_SIZE(fields); q++) {
@@ -4436,7 +4443,6 @@ 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_to_shadow_sync = false;-- 1.8.3.1
linux-stable-mirror@lists.linaro.org
-
Liran Alon -
Paolo Bonzini