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Commit bb85717e authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Sasha Levin
Browse files

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



commit f8be156be163a052a067306417cd0ff679068c97 upstream.

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: default avatarNicholas Piggin <npiggin@gmail.com>
Tested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d6f751ec

virt/kvm/kvm_main.c

+17 −2
Original line number Diff line number Diff line
@@ -1593,6 +1593,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault) 
	return true;

}



static int kvm_try_get_pfn(kvm_pfn_t pfn)

{

	if (kvm_is_reserved_pfn(pfn))

		return 1;

	return get_page_unless_zero(pfn_to_page(pfn));

}



static int hva_to_pfn_remapped(struct vm_area_struct *vma,

			       unsigned long addr, bool *async,

			       bool write_fault, bool *writable,
@@ -1642,13 +1649,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, 
	 * Whoever called remap_pfn_range is also going to call e.g.

	 * unmap_mapping_range before the underlying pages are freed,

	 * causing a call to our MMU notifier.

	 *

	 * Certain IO or PFNMAP mappings can be backed with valid

	 * struct pages, but be allocated without refcounting e.g.,

	 * tail pages of non-compound higher order allocations, which

	 * would then underflow the refcount when the caller does the

	 * required put_page. Don't allow those pages here.

	 */ 

	kvm_get_pfn(pfn);

	if (!kvm_try_get_pfn(pfn))

		r = -EFAULT;



out:

	pte_unmap_unlock(ptep, ptl);

	*p_pfn = pfn;

	return 0;



	return r;

}



/*