[PATCH 5.17 066/219] KVM: arm64: mixed-width check should be skipped for uninitialized vCPUs

Greg Kroah-Hartman
2022-04-18T12:21:24Z

From: Reiji Watanabe <reijiw@google.com>

[ Upstream commit 26bf74bd9f6ff0f1545b4f0c92a37c232d076014 ]

KVM allows userspace to configure either all EL1 32bit or 64bit vCPUs
for a guest. At vCPU reset, vcpu_allowed_register_width() checks
if the vcpu's register width is consistent with all other vCPUs'.
Since the checking is done even against vCPUs that are not initialized
(KVM_ARM_VCPU_INIT has not been done) yet, the uninitialized vCPUs
are erroneously treated as 64bit vCPU, which causes the function to
incorrectly detect a mixed-width VM.

Introduce KVM_ARCH_FLAG_EL1_32BIT and KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED
bits for kvm->arch.flags. A value of the EL1_32BIT bit indicates that
the guest needs to be configured with all 32bit or 64bit vCPUs, and
a value of the REG_WIDTH_CONFIGURED bit indicates if a value of the
EL1_32BIT bit is valid (already set up). Values in those bits are set at
the first KVM_ARM_VCPU_INIT for the guest based on KVM_ARM_VCPU_EL1_32BIT
configuration for the vCPU.

Check vcpu's register width against those new bits at the vcpu's
KVM_ARM_VCPU_INIT (instead of against other vCPUs' register width).

Fixes: 66e94d5cafd4 ("KVM: arm64: Prevent mixed-width VM creation")
Signed-off-by: Reiji Watanabe <reijiw@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220329031924.619453-2-reijiw@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/kvm_emulate.h | 27 ++++++++----
arch/arm64/include/asm/kvm_host.h | 10 +++++
arch/arm64/kvm/reset.c | 65 +++++++++++++++++++---------
3 files changed, 74 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index d62405ce3e6d..7496deab025a 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -43,10 +43,22 @@ void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr);

void kvm_vcpu_wfi(struct kvm_vcpu *vcpu);

+#if defined(__KVM_VHE_HYPERVISOR__) || defined(__KVM_NVHE_HYPERVISOR__)
static __always_inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu)
{
return !(vcpu->arch.hcr_el2 & HCR_RW);
}
+#else
+static __always_inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+
+ WARN_ON_ONCE(!test_bit(KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED,
+ &kvm->arch.flags));
+
+ return test_bit(KVM_ARCH_FLAG_EL1_32BIT, &kvm->arch.flags);
+}
+#endif

static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
{
@@ -72,15 +84,14 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
vcpu->arch.hcr_el2 |= HCR_TVM;
}

- if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features))
+ if (vcpu_el1_is_32bit(vcpu))
vcpu->arch.hcr_el2 &= ~HCR_RW;
-
- /*
- * TID3: trap feature register accesses that we virtualise.
- * For now this is conditional, since no AArch32 feature regs
- * are currently virtualised.
- */
- if (!vcpu_el1_is_32bit(vcpu))
+ else
+ /*
+ * TID3: trap feature register accesses that we virtualise.
+ * For now this is conditional, since no AArch32 feature regs
+ * are currently virtualised.
+ */
vcpu->arch.hcr_el2 |= HCR_TID3;

if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) ||
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 2619fda42ca2..b5ae92f77c61 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -127,6 +127,16 @@ struct kvm_arch {
#define KVM_ARCH_FLAG_MTE_ENABLED 1
/* At least one vCPU has ran in the VM */
#define KVM_ARCH_FLAG_HAS_RAN_ONCE 2
+ /*
+ * The following two bits are used to indicate the guest's EL1
+ * register width configuration. A value of KVM_ARCH_FLAG_EL1_32BIT
+ * bit is valid only when KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED is set.
+ * Otherwise, the guest's EL1 register width has not yet been
+ * determined yet.
+ */
+#define KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED 3
+#define KVM_ARCH_FLAG_EL1_32BIT 4
+
unsigned long flags;

/*
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index ecc40c8cd6f6..6c70c6f61c70 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -181,27 +181,51 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
return 0;
}

-static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
+/**
+ * kvm_set_vm_width() - set the register width for the guest
+ * @vcpu: Pointer to the vcpu being configured
+ *
+ * Set both KVM_ARCH_FLAG_EL1_32BIT and KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED
+ * in the VM flags based on the vcpu's requested register width, the HW
+ * capabilities and other options (such as MTE).
+ * When REG_WIDTH_CONFIGURED is already set, the vcpu settings must be
+ * consistent with the value of the FLAG_EL1_32BIT bit in the flags.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+static int kvm_set_vm_width(struct kvm_vcpu *vcpu)
{
- struct kvm_vcpu *tmp;
+ struct kvm *kvm = vcpu->kvm;
bool is32bit;
- unsigned long i;

is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT);
+
+ lockdep_assert_held(&kvm->lock);
+
+ if (test_bit(KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED, &kvm->arch.flags)) {
+ /*
+ * The guest's register width is already configured.
+ * Make sure that the vcpu is consistent with it.
+ */
+ if (is32bit == test_bit(KVM_ARCH_FLAG_EL1_32BIT, &kvm->arch.flags))
+ return 0;
+
+ return -EINVAL;
+ }
+
if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1) && is32bit)
- return false;
+ return -EINVAL;

/* MTE is incompatible with AArch32 */
- if (kvm_has_mte(vcpu->kvm) && is32bit)
- return false;
+ if (kvm_has_mte(kvm) && is32bit)
+ return -EINVAL;

- /* 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;
- }
+ if (is32bit)
+ set_bit(KVM_ARCH_FLAG_EL1_32BIT, &kvm->arch.flags);

- return true;
+ set_bit(KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED, &kvm->arch.flags);
+
+ return 0;
}

/**
@@ -230,10 +254,16 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
u32 pstate;

mutex_lock(&vcpu->kvm->lock);
- reset_state = vcpu->arch.reset_state;
- WRITE_ONCE(vcpu->arch.reset_state.reset, false);
+ ret = kvm_set_vm_width(vcpu);
+ if (!ret) {
+ reset_state = vcpu->arch.reset_state;
+ WRITE_ONCE(vcpu->arch.reset_state.reset, false);
+ }
mutex_unlock(&vcpu->kvm->lock);

+ if (ret)
+ return ret;
+
/* Reset PMU outside of the non-preemptible section */
kvm_pmu_vcpu_reset(vcpu);

@@ -260,14 +290,9 @@ 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 (vcpu_el1_is_32bit(vcpu)) {
pstate = VCPU_RESET_PSTATE_SVC;
} else {
pstate = VCPU_RESET_PSTATE_EL1;
--
2.35.1