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, 2 insertions, 1 deletions

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 62de0768d6aa..48fad6556822 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -5645,7 +5645,8 @@ with the KVM_XEN_VCPU_GET_ATTR ioctl.
   };
 
 Copies Memory Tagging Extension (MTE) tags to/from guest tag memory. The
-``guest_ipa`` and ``length`` fields must be ``PAGE_SIZE`` aligned. The ``addr``
+``guest_ipa`` and ``length`` fields must be ``PAGE_SIZE`` aligned.
+``length`` must not be bigger than 2^31 - PAGE_SIZE bytes. The ``addr``
 field must point to a buffer which the tags will be copied to or from.
 
 ``flags`` specifies the direction of copy, either ``KVM_ARM_TAGS_TO_GUEST`` or