tree 2f291bec641f75e1f350177da6179e8316699d71
parent 309505dd56854c1f9744c9a2b8aa40d897002bca
author Nicholas Piggin <npiggin@gmail.com> 1624537744 -0400
committer Paolo Bonzini <pbonzini@redhat.com> 1624550111 -0400

KVM: do not allow mapping valid but non-reference-counted pages

It's possible to create a region which maps valid but non-refcounted
pages (e.g., tail pages of non-compound higher order allocations). These
host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family
of APIs, which take a reference to the page, which takes it from 0 to 1.
When the reference is dropped, this will free the page incorrectly.

Fix this by only taking a reference on valid pages if it was non-zero,
which indicates it is participating in normal refcounting (and can be
released with put_page).

This addresses CVE-2021-22543.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>