From 8782fb61cc848364e1e1599d76d3c9dd58a1cc06 Mon Sep 17 00:00:00 2001 From: Steven Price Date: Fri, 2 Sep 2022 12:26:12 +0100 Subject: mm: pagewalk: Fix race between unmap and page walker The mmap lock protects the page walker from changes to the page tables during the walk. However a read lock is insufficient to protect those areas which don't have a VMA as munmap() detaches the VMAs before downgrading to a read lock and actually tearing down PTEs/page tables. For users of walk_page_range() the solution is to simply call pte_hole() immediately without checking the actual page tables when a VMA is not present. We now never call __walk_page_range() without a valid vma. For walk_page_range_novma() the locking requirements are tightened to require the mmap write lock to be taken, and then walking the pgd directly with 'no_vma' set. This in turn means that all page walkers either have a valid vma, or it's that special 'novma' case for page table debugging. As a result, all the odd '(!walk->vma && !walk->no_vma)' tests can be removed. Fixes: dd2283f2605e ("mm: mmap: zap pages with read mmap_sem in munmap") Reported-by: Jann Horn Signed-off-by: Steven Price Cc: Vlastimil Babka Cc: Thomas Hellström Cc: Konstantin Khlebnikov Cc: Andrew Morton Signed-off-by: Linus Torvalds --- arch/riscv/mm/pageattr.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch') diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c index 5e49e4b4a4cc..86c56616e5de 100644 --- a/arch/riscv/mm/pageattr.c +++ b/arch/riscv/mm/pageattr.c @@ -118,10 +118,10 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask, if (!numpages) return 0; - mmap_read_lock(&init_mm); + mmap_write_lock(&init_mm); ret = walk_page_range_novma(&init_mm, start, end, &pageattr_ops, NULL, &masks); - mmap_read_unlock(&init_mm); + mmap_write_unlock(&init_mm); flush_tlb_kernel_range(start, end); -- cgit v1.2.3