[PATCH 5.12 073/296] KVM: arm64: Prevent mixed-width VM creation

Greg Kroah-Hartman
2021-05-31T16:10:13Z

From: Marc Zyngier <maz@kernel.org>

commit 66e94d5cafd4decd4f92d16a022ea587d7f4094f upstream.

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
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20210524170752.1549797-1-maz@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/include/asm/kvm_emulate.h | 5 +++++
arch/arm64/kvm/reset.c | 28 ++++++++++++++++++++++++----
2 files changed, 29 insertions(+), 4 deletions(-)

--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -463,4 +463,9 @@ static __always_inline void kvm_incr_pc(
vcpu->arch.flags |= KVM_ARM64_INCREMENT_PC;
}

+static inline bool vcpu_has_feature(struct kvm_vcpu *vcpu, int feature)
+{
+ return test_bit(feature, vcpu->arch.features);
+}
+
#endif /* __ARM64_KVM_EMULATE_H__ */
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -170,6 +170,25 @@ static int kvm_vcpu_enable_ptrauth(struc
return 0;
}

+static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu *tmp;
+ bool is32bit;
+ int i;
+
+ is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT);
+ if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit)
+ return false;
+
+ /* Check that the vcpus are either all 32bit or all 64bit */
+ kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
+ if (vcpu_has_feature(tmp, KVM_ARM_VCPU_EL1_32BIT) != is32bit)
+ return false;
+ }
+
+ return true;
+}
+
/**
* kvm_reset_vcpu - sets core registers and sys_regs to reset value
* @vcpu: The VCPU pointer
@@ -221,13 +240,14 @@ 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;