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mm: add early FAULT_FLAG_UNSHARE consistency checks 

For now, FAULT_FLAG_UNSHARE only applies to anonymous pages, which
implies a COW mapping. Let's hide FAULT_FLAG_UNSHARE early if we're not
dealing with a COW mapping, such that we treat it like a read fault as
documented and don't have to worry about the flag throughout all fault
handlers.

While at it, centralize the check for mutual exclusion of
FAULT_FLAG_UNSHARE and FAULT_FLAG_WRITE and just drop the check that
either flag is set in the WP handler.

Link: https://lkml.kernel.org/r/20221116102659.70287-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-11-16 11:26:43 +01:00 committed by Andrew Morton
parent 97713a3abe
commit cdc5021cda
3 changed files with 20 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
mm/huge_memory.c
View File

@ -1313,9 +1313,6 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
VM_BUG_ON_VMA(!vma->anon_vma, vma);
VM_BUG_ON(unshare && (vmf->flags & FAULT_FLAG_WRITE));
VM_BUG_ON(!unshare && !(vmf->flags & FAULT_FLAG_WRITE));
if (is_huge_zero_pmd(orig_pmd))
goto fallback;

5
mm/hugetlb.c
View File

@ -5316,9 +5316,6 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
unsigned long haddr = address & huge_page_mask(h);
struct mmu_notifier_range range;
VM_BUG_ON(unshare && (flags & FOLL_WRITE));
VM_BUG_ON(!unshare && !(flags & FOLL_WRITE));
/*
* hugetlb does not support FOLL_FORCE-style write faults that keep the
* PTE mapped R/O such as maybe_mkwrite() would do.
@ -5328,8 +5325,6 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
/* Let's take out MAP_SHARED mappings first. */
if (vma->vm_flags & VM_MAYSHARE) {
if (unlikely(unshare))
return 0;
set_huge_ptep_writable(vma, haddr, ptep);
return 0;
}

23
mm/memory.c
View File

@ -3343,9 +3343,6 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
struct vm_area_struct *vma = vmf->vma;
struct folio *folio;
VM_BUG_ON(unshare && (vmf->flags & FAULT_FLAG_WRITE));
VM_BUG_ON(!unshare && !(vmf->flags & FAULT_FLAG_WRITE));
if (likely(!unshare)) {
if (userfaultfd_pte_wp(vma, *vmf->pte)) {
pte_unmap_unlock(vmf->pte, vmf->ptl);
@ -5161,6 +5158,22 @@ static void lru_gen_exit_fault(void)
}
#endif /* CONFIG_LRU_GEN */
static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
unsigned int *flags)
{
if (unlikely(*flags & FAULT_FLAG_UNSHARE)) {
if (WARN_ON_ONCE(*flags & FAULT_FLAG_WRITE))
return VM_FAULT_SIGSEGV;
/*
* FAULT_FLAG_UNSHARE only applies to COW mappings. Let's
* just treat it like an ordinary read-fault otherwise.
*/
if (!is_cow_mapping(vma->vm_flags))
*flags &= ~FAULT_FLAG_UNSHARE;
}
return 0;
}
/*
* By the time we get here, we already hold the mm semaphore
*
@ -5177,6 +5190,10 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
count_vm_event(PGFAULT);
count_memcg_event_mm(vma->vm_mm, PGFAULT);
ret = sanitize_fault_flags(vma, &flags);
if (ret)
return ret;
if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
flags & FAULT_FLAG_INSTRUCTION,
flags & FAULT_FLAG_REMOTE))