From: Sean Christopherson <seanjc@google.com>
Date: Thu, 4 Nov 2021 00:25:03 +0000
Subject: KVM: Disallow user memslot with size that exceeds "unsigned long"
Git-commit: 6b285a5587506bae084cf9a3ed5aa491d623b91b
Patch-mainline: v5.16-rc4
References: git-fixes

Reject userspace memslots whose size exceeds the storage capacity of an
"unsigned long".  KVM's uAPI takes the size as u64 to support large slots
on 64-bit hosts, but does not account for the size being truncated on
32-bit hosts in various flows.  The access_ok() check on the userspace
virtual address in particular casts the size to "unsigned long" and will
check the wrong number of bytes.

KVM doesn't actually support slots whose size doesn't fit in an "unsigned
long", e.g. KVM's internal kvm_memory_slot.npages is an "unsigned long",
not a "u64", and misc arch specific code follows that behavior.

Fixes: fa3d315a4ce2 ("KVM: Validate userspace_addr of memslot when registered")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <20211104002531.1176691-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Ivan T. Ivanov <iivanov@suse.de>
---
 virt/kvm/kvm_main.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1606,7 +1606,8 @@ int __kvm_set_memory_region(struct kvm *
 	id = (u16)mem->slot;
 
 	/* General sanity checks */
-	if (mem->memory_size & (PAGE_SIZE - 1))
+	if ((mem->memory_size & (PAGE_SIZE - 1)) ||
+	    (mem->memory_size != (unsigned long)mem->memory_size))
 		return -EINVAL;
 	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
 		return -EINVAL;