KVM: arm64: Limit length in kvm_vm_ioctl_mte_copy_tags() to INT_MAX

In case of success, this function returns the amount of handled bytes.
However, this does not work for large values: The function is called
from kvm_arch_vm_ioctl() (which still returns a long), which in turn
is called from kvm_vm_ioctl() in virt/kvm/kvm_main.c. And that function
stores the return value in an "int r" variable. So the upper 32-bits
of the "long" return value are lost there.

KVM ioctl functions should only return "int" values, so let's limit
the amount of bytes that can be requested here to INT_MAX to avoid
the problem with the truncated return value. We can then also change
the return type of the function to "int" to make it clearer that it
is not possible to return a "long" here.

Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Message-Id: <20230208140105.655814-5-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 07444fa22888..26a2ebc465ea 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -1019,8 +1019,8 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
 	return ret;
 }
 
-long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
-				struct kvm_arm_copy_mte_tags *copy_tags)
+int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
+			       struct kvm_arm_copy_mte_tags *copy_tags)
 {
 	gpa_t guest_ipa = copy_tags->guest_ipa;
 	size_t length = copy_tags->length;
@@ -1041,6 +1041,10 @@ long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
 	if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK)
 		return -EINVAL;
 
+	/* Lengths above INT_MAX cannot be represented in the return value */
+	if (length > INT_MAX)
+		return -EINVAL;
+
 	gfn = gpa_to_gfn(guest_ipa);
 
 	mutex_lock(&kvm->slots_lock);