Re: [PATCH] KVM: arm64: Prevent mixed-width VM creation
From: Mark Rutland <mark.rutland@arm.com>
Date: 2021-05-20 12:46:37
Also in:
kvmarm, stable
On Thu, May 20, 2021 at 01:22:53PM +0100, Marc Zyngier wrote:
quoted hunk ↗ jump to hunk
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.
quoted hunk ↗ jump to hunk
+ + 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
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