* [PATCH] KVM: arm64: Prevent mixed-width VM creation
@ 2021-05-20 12:22 Marc Zyngier
2021-05-20 12:44 ` Mark Rutland
0 siblings, 1 reply; 4+ messages in thread
From: Marc Zyngier @ 2021-05-20 12:22 UTC (permalink / raw)
To: linux-arm-kernel, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandru Elisei, kernel-team,
Steven Price, stable
It looks like we have tolerated creating mixed-width VMs since...
forever. However, that was never the intention, and we'd rather
not have to support that pointless complexity.
Forbid such a setup by making sure all the vcpus have the same
register width.
Reported-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
---
arch/arm64/kvm/reset.c | 28 ++++++++++++++++++++++++----
1 file changed, 24 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 956cdc240148..1cf308be6ef3 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -166,6 +166,25 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
return 0;
}
+static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu *tmp;
+ int i;
+
+ /* Check that the vcpus are either all 32bit or all 64bit */
+ kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
+ bool w;
+
+ w = test_bit(KVM_ARM_VCPU_EL1_32BIT, tmp->arch.features);
+ w ^= test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
+
+ if (w)
+ return false;
+ }
+
+ return true;
+}
+
/**
* kvm_reset_vcpu - sets core registers and sys_regs to reset value
* @vcpu: The VCPU pointer
@@ -217,13 +236,14 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
}
}
+ if (!vcpu_allowed_register_width(vcpu)) {
+ ret = -EINVAL;
+ goto out;
+ }
+
switch (vcpu->arch.target) {
default:
if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
- if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
- ret = -EINVAL;
- goto out;
- }
pstate = VCPU_RESET_PSTATE_SVC;
} else {
pstate = VCPU_RESET_PSTATE_EL1;
--
2.30.2
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^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: arm64: Prevent mixed-width VM creation
2021-05-20 12:22 [PATCH] KVM: arm64: Prevent mixed-width VM creation Marc Zyngier
@ 2021-05-20 12:44 ` Mark Rutland
2021-05-20 12:58 ` Marc Zyngier
0 siblings, 1 reply; 4+ messages in thread
From: Mark Rutland @ 2021-05-20 12:44 UTC (permalink / raw)
To: Marc Zyngier; +Cc: linux-arm-kernel, kvmarm, kernel-team, stable, Steven Price
On Thu, May 20, 2021 at 01:22:53PM +0100, Marc Zyngier wrote:
> It looks like we have tolerated creating mixed-width VMs since...
> forever. However, that was never the intention, and we'd rather
> not have to support that pointless complexity.
>
> Forbid such a setup by making sure all the vcpus have the same
> register width.
>
> Reported-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: stable@vger.kernel.org
> ---
> arch/arm64/kvm/reset.c | 28 ++++++++++++++++++++++++----
> 1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index 956cdc240148..1cf308be6ef3 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -166,6 +166,25 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> +static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> +{
> + struct kvm_vcpu *tmp;
> + int i;
> +
> + /* Check that the vcpus are either all 32bit or all 64bit */
> + kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> + bool w;
> +
> + w = test_bit(KVM_ARM_VCPU_EL1_32BIT, tmp->arch.features);
> + w ^= test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
> +
> + if (w)
> + return false;
> + }
I think this is wrong for a single-cpu VM. In that case, the loop will
have a single iteration, and tmp == vcpu, so w must be 0 regardless of
the value of arch.features.
IIUC that doesn't prevent KVM_ARM_VCPU_EL1_32BIT being set when we don't
have the ARM64_HAS_32BIT_EL1 cap, unless that's checked elsewhere?
How about something like:
| static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
| {
| bool is_32bit = vcpu_features_32bit(vcpu);
| struct kvm_vcpu *tmp;
| int i;
|
| if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is_32bit)
| return false;
|
| kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
| if (is_32bit != vcpu_features_32bit(tmp))
| return false;
| }
|
| return true;
| }
... with a helper in <asm/kvm_emulate.h> like:
| static bool vcpu_features_32bit(struct kvm_vcpu *vcpu)
| {
| return test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
| }
... or
| static inline bool vcpu_has_feature(struct kvm_vcpu *vcpu, int feature)
| {
| return test_bit(feature, vcpu->arch.features);
| }
... so that we can avoid the line splitting required by the length of
the test_bit() expression?
Thanks,
Mark.
> +
> + return true;
> +}
> +
> /**
> * kvm_reset_vcpu - sets core registers and sys_regs to reset value
> * @vcpu: The VCPU pointer
> @@ -217,13 +236,14 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> }
> }
>
> + if (!vcpu_allowed_register_width(vcpu)) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> switch (vcpu->arch.target) {
> default:
> if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
> - if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
> - ret = -EINVAL;
> - goto out;
> - }
> pstate = VCPU_RESET_PSTATE_SVC;
> } else {
> pstate = VCPU_RESET_PSTATE_EL1;
> --
> 2.30.2
>
> _______________________________________________
> kvmarm mailing list
> kvmarm@lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: arm64: Prevent mixed-width VM creation
2021-05-20 12:44 ` Mark Rutland
@ 2021-05-20 12:58 ` Marc Zyngier
2021-05-20 14:06 ` Mark Rutland
0 siblings, 1 reply; 4+ messages in thread
From: Marc Zyngier @ 2021-05-20 12:58 UTC (permalink / raw)
To: Mark Rutland; +Cc: linux-arm-kernel, kvmarm, kernel-team, stable, Steven Price
On Thu, 20 May 2021 13:44:34 +0100,
Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Thu, May 20, 2021 at 01:22:53PM +0100, Marc Zyngier wrote:
> > It looks like we have tolerated creating mixed-width VMs since...
> > forever. However, that was never the intention, and we'd rather
> > not have to support that pointless complexity.
> >
> > Forbid such a setup by making sure all the vcpus have the same
> > register width.
> >
> > Reported-by: Steven Price <steven.price@arm.com>
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Cc: stable@vger.kernel.org
> > ---
> > arch/arm64/kvm/reset.c | 28 ++++++++++++++++++++++++----
> > 1 file changed, 24 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> > index 956cdc240148..1cf308be6ef3 100644
> > --- a/arch/arm64/kvm/reset.c
> > +++ b/arch/arm64/kvm/reset.c
> > @@ -166,6 +166,25 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
> > return 0;
> > }
> >
> > +static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> > +{
> > + struct kvm_vcpu *tmp;
> > + int i;
> > +
> > + /* Check that the vcpus are either all 32bit or all 64bit */
> > + kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> > + bool w;
> > +
> > + w = test_bit(KVM_ARM_VCPU_EL1_32BIT, tmp->arch.features);
> > + w ^= test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
> > +
> > + if (w)
> > + return false;
> > + }
>
> I think this is wrong for a single-cpu VM. In that case, the loop will
> have a single iteration, and tmp == vcpu, so w must be 0 regardless of
> the value of arch.features.
I don't immediately see what is wrong with a single-cpu VM. 'w' will
be zero indeed, and we'll return that this is allowed. After all, each
VM starts by being a single-CPU VM.
But of course...
> IIUC that doesn't prevent KVM_ARM_VCPU_EL1_32BIT being set when we don't
> have the ARM64_HAS_32BIT_EL1 cap, unless that's checked elsewhere?
... I mistakenly removed the check against ARM64_HAS_32BIT_EL1...
>
> How about something like:
>
> | static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> | {
> | bool is_32bit = vcpu_features_32bit(vcpu);
> | struct kvm_vcpu *tmp;
> | int i;
> |
> | if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is_32bit)
> | return false;
> |
> | kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> | if (is_32bit != vcpu_features_32bit(tmp))
> | return false;
> | }
> |
> | return true;
> | }
>
> ... with a helper in <asm/kvm_emulate.h> like:
>
> | static bool vcpu_features_32bit(struct kvm_vcpu *vcpu)
> | {
> | return test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
> | }
>
> ... or
>
> | static inline bool vcpu_has_feature(struct kvm_vcpu *vcpu, int feature)
> | {
> | return test_bit(feature, vcpu->arch.features);
> | }
>
> ... so that we can avoid the line splitting required by the length of
> the test_bit() expression?
Yup, looks OK to me (with a preference for the latter).
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] KVM: arm64: Prevent mixed-width VM creation
2021-05-20 12:58 ` Marc Zyngier
@ 2021-05-20 14:06 ` Mark Rutland
0 siblings, 0 replies; 4+ messages in thread
From: Mark Rutland @ 2021-05-20 14:06 UTC (permalink / raw)
To: Marc Zyngier; +Cc: linux-arm-kernel, kvmarm, kernel-team, stable, Steven Price
On Thu, May 20, 2021 at 01:58:55PM +0100, Marc Zyngier wrote:
> On Thu, 20 May 2021 13:44:34 +0100,
> Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > On Thu, May 20, 2021 at 01:22:53PM +0100, Marc Zyngier wrote:
> > > It looks like we have tolerated creating mixed-width VMs since...
> > > forever. However, that was never the intention, and we'd rather
> > > not have to support that pointless complexity.
> > >
> > > Forbid such a setup by making sure all the vcpus have the same
> > > register width.
> > >
> > > Reported-by: Steven Price <steven.price@arm.com>
> > > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > > Cc: stable@vger.kernel.org
> > > ---
> > > arch/arm64/kvm/reset.c | 28 ++++++++++++++++++++++++----
> > > 1 file changed, 24 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> > > index 956cdc240148..1cf308be6ef3 100644
> > > --- a/arch/arm64/kvm/reset.c
> > > +++ b/arch/arm64/kvm/reset.c
> > > @@ -166,6 +166,25 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
> > > return 0;
> > > }
> > >
> > > +static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> > > +{
> > > + struct kvm_vcpu *tmp;
> > > + int i;
> > > +
> > > + /* Check that the vcpus are either all 32bit or all 64bit */
> > > + kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> > > + bool w;
> > > +
> > > + w = test_bit(KVM_ARM_VCPU_EL1_32BIT, tmp->arch.features);
> > > + w ^= test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
> > > +
> > > + if (w)
> > > + return false;
> > > + }
> >
> > I think this is wrong for a single-cpu VM. In that case, the loop will
> > have a single iteration, and tmp == vcpu, so w must be 0 regardless of
> > the value of arch.features.
>
> I don't immediately see what is wrong with a single-cpu VM. 'w' will
> be zero indeed, and we'll return that this is allowed. After all, each
> VM starts by being a single-CPU VM.
Sorry; I should have been clearer. I had assumed that this was trying to
rely on a difference across vcpus implicitly providing an equivalent of
the removed check for the KVM_ARM_VCPU_EL1_32BIT cap. I guess from the
below that was not the case. :)
Thanks,
Mark.
> But of course...
>
> > IIUC that doesn't prevent KVM_ARM_VCPU_EL1_32BIT being set when we don't
> > have the ARM64_HAS_32BIT_EL1 cap, unless that's checked elsewhere?
>
> ... I mistakenly removed the check against ARM64_HAS_32BIT_EL1...
>
> >
> > How about something like:
> >
> > | static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
> > | {
> > | bool is_32bit = vcpu_features_32bit(vcpu);
> > | struct kvm_vcpu *tmp;
> > | int i;
> > |
> > | if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is_32bit)
> > | return false;
> > |
> > | kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
> > | if (is_32bit != vcpu_features_32bit(tmp))
> > | return false;
> > | }
> > |
> > | return true;
> > | }
> >
> > ... with a helper in <asm/kvm_emulate.h> like:
> >
> > | static bool vcpu_features_32bit(struct kvm_vcpu *vcpu)
> > | {
> > | return test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features);
> > | }
> >
> > ... or
> >
> > | static inline bool vcpu_has_feature(struct kvm_vcpu *vcpu, int feature)
> > | {
> > | return test_bit(feature, vcpu->arch.features);
> > | }
> >
> > ... so that we can avoid the line splitting required by the length of
> > the test_bit() expression?
>
> Yup, looks OK to me (with a preference for the latter).
>
> Thanks,
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-05-20 12:22 [PATCH] KVM: arm64: Prevent mixed-width VM creation Marc Zyngier
2021-05-20 12:44 ` Mark Rutland
2021-05-20 12:58 ` Marc Zyngier
2021-05-20 14:06 ` Mark Rutland
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