Re: [stable-5.4][PATCH] KVM: Forbid the use of tagged userspace addresses for memslots

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Feb 01, 2021 at 02:38:05PM +0100, Paolo Bonzini wrote:
> On 01/02/21 14:31, Marc Zyngier wrote:
> > commit 139bc8a6146d92822c866cf2fd410159c56b3648 upstream.
> > 
> > The use of a tagged address could be pretty confusing for the
> > whole memslot infrastructure as well as the MMU notifiers.
> > 
> > Forbid it altogether, as it never quite worked the first place.
> > 
> > Cc: stable@vger.kernel.org
> > Reported-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >   Documentation/virt/kvm/api.txt | 3 +++
> >   virt/kvm/kvm_main.c            | 1 +
> >   2 files changed, 4 insertions(+)
> > 
> > diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
> > index a18e996fa54b..7064efd3b5ea 100644
> > --- a/Documentation/virt/kvm/api.txt
> > +++ b/Documentation/virt/kvm/api.txt
> > @@ -1132,6 +1132,9 @@ field userspace_addr, which must point at user addressable memory for
> >   the entire memory slot size.  Any object may back this memory, including
> >   anonymous memory, ordinary files, and hugetlbfs.
> > +On architectures that support a form of address tagging, userspace_addr must
> > +be an untagged address.
> > +
> >   It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
> >   be identical.  This allows large pages in the guest to be backed by large
> >   pages in the host.
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 8f3b40ec02b7..f25b5043cbca 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1017,6 +1017,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >   	/* We can read the guest memory with __xxx_user() later on. */
> >   	if ((id < KVM_USER_MEM_SLOTS) &&
> >   	    ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
> > +	     (mem->userspace_addr != untagged_addr(mem->userspace_addr)) ||
> >   	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
> >   			mem->memory_size)))
> >   		goto out;
> > 
> 
> Indeed untagged_addr was added in 5.3.
> 
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Now queued up, thanks.

greg k-h