[PATCH 1/1] mm/huge_memory: disallow raw PMD mappings of the huge zero page

[Lance Yang]

vm_mixed_zeropage_allowed() validates zeropage insertion into
VM_MIXEDMAP VMAs. No in-tree user needs to insert the huge zero page
through vmf_insert_pfn_pmd().

Return VM_FAULT_SIGBUS if vmf_insert_pfn_pmd() is asked to map it.

Link: https://lore.kernel.org/linux-mm/f76beaf8-351a-4b22-b362-a945a5e1af6a@xxxxxxxxxx/
Suggested-by: Kiryl Shutsemau <kas@xxxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Lance Yang <lance.yang@xxxxxxxxx>
---
 mm/huge_memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index bfd972b997f9..c02f21ce4f4c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1728,6 +1728,9 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, unsigned long pfn,
 						(VM_PFNMAP|VM_MIXEDMAP));
 	BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma));
 
+	if (unlikely(is_huge_zero_pfn(pfn)))
+		return VM_FAULT_SIGBUS;
+
 	pfnmap_setup_cachemode_pfn(pfn, &pgprot);
 
 	return insert_pmd(vma, addr, vmf->pmd, fop, pgprot, write);
-- 
2.39.3 (Apple Git-146)