A selftests fix for ARM, and the fix for page reference count underflow.
This is a very small fix that was provided by Nick Piggin and tested
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 <firstname.lastname@example.org>
Tested-by: Paolo Bonzini <email@example.com>
Signed-off-by: Paolo Bonzini <firstname.lastname@example.org>
1 file changed