x86/xen: avoid writing to freed memory after race in p2m handling (239af7c7) · Commits · 戴 / test

In case a race was detected during allocation of a new p2m tree element in alloc_p2m() the new allocated mid_mfn page is freed without updating the pointer to the found value in the tree. This will result in overwriting the just freed page with the mfn of the p2m leaf. Signed-off-by:

Juergen Gross <jgross@suse.com> Signed-off-by:

David Vrabel <david.vrabel@citrix.com>

arch/x86/xen/p2m.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -566,6 +566,7 @@ static bool alloc_p2m(unsigned long pfn)
		/* Separately check the mid mfn level */
		unsigned long missing_mfn;
		unsigned long mid_mfn_mfn;
		unsigned long old_mfn;

		mid_mfn = alloc_p2m_page();
		if (!mid_mfn)
		@@ -575,11 +576,14 @@ static bool alloc_p2m(unsigned long pfn)

		missing_mfn = virt_to_mfn(p2m_mid_missing_mfn);
		mid_mfn_mfn = virt_to_mfn(mid_mfn);
		if (cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn) != missing_mfn)
		old_mfn = cmpxchg(top_mfn_p, missing_mfn, mid_mfn_mfn);
		if (old_mfn != missing_mfn) {
		free_p2m_page(mid_mfn);
		else
		mid_mfn = mfn_to_virt(old_mfn);
		} else {
		p2m_top_mfn_p[topidx] = mid_mfn;
		}
		}

		if (p2m_top[topidx][mididx] == p2m_identity \|\|
		p2m_top[topidx][mididx] == p2m_missing) {

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