APPLIED: [PATCH] mm: thp: fix /dev/zero MAP_PRIVATE and vm_flags cleanups - CVE-2011-2479
Tim Gardner
tim.gardner at canonical.com
Fri Oct 14 15:24:48 UTC 2011
On 10/14/2011 04:01 PM, Paolo Pisati wrote:
> From: Andrea Arcangeli<aarcange at redhat.com>
>
> CVE-2011-2479
>
> BugLink: http://bugs.launchpad.net/bugs/775809
>
> commit 78f11a255749d09025f54d4e2df4fbcb031530e2 upstream.
>
> The huge_memory.c THP page fault was allowed to run if vm_ops was null
> (which would succeed for /dev/zero MAP_PRIVATE, as the f_op->mmap wouldn't
> setup a special vma->vm_ops and it would fallback to regular anonymous
> memory) but other THP logics weren't fully activated for vmas with vm_file
> not NULL (/dev/zero has a not NULL vma->vm_file).
>
> So this removes the vm_file checks so that /dev/zero also can safely use
> THP (the other albeit safer approach to fix this bug would have been to
> prevent the THP initial page fault to run if vm_file was set).
>
> After removing the vm_file checks, this also makes huge_memory.c stricter
> in khugepaged for the DEBUG_VM=y case. It doesn't replace the vm_file
> check with a is_pfn_mapping check (but it keeps checking for VM_PFNMAP
> under VM_BUG_ON) because for a is_cow_mapping() mapping VM_PFNMAP should
> only be allowed to exist before the first page fault, and in turn when
> vma->anon_vma is null (so preventing khugepaged registration). So I tend
> to think the previous comment saying if vm_file was set, VM_PFNMAP might
> have been set and we could still be registered in khugepaged (despite
> anon_vma was not NULL to be registered in khugepaged) was too paranoid.
> The is_linear_pfn_mapping check is also I think superfluous (as described
> by comment) but under DEBUG_VM it is safe to stay.
>
> Addresses https://bugzilla.kernel.org/show_bug.cgi?id=33682
>
> Signed-off-by: Andrea Arcangeli<aarcange at redhat.com>
> Reported-by: Caspar Zhang<bugs at casparzhang.com>
> Acked-by: Mel Gorman<mel at csn.ul.ie>
> Acked-by: Rik van Riel<riel at redhat.com>
> Signed-off-by: Andrew Morton<akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds<torvalds at linux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman<gregkh at suse.de>
> Signed-off-by: Tim Gardner<tim.gardner at canonical.com>
>
> (cherry picked from commit 3a7ecd0f369bc80f3647941224c3c24b7dcb9621)
> Signed-off-by: Paolo Pisati<paolo.pisati at canonical.com>
> Acked-by: Andy Whitcroft<apw at canonical.com>
> ---
> include/linux/huge_mm.h | 2 +-
> include/linux/mm.h | 3 ++-
> mm/huge_memory.c | 43 ++++++++++++++++++++++++-------------------
> 3 files changed, 27 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index df29c8f..8847c8c 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -117,7 +117,7 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
> unsigned long end,
> long adjust_next)
> {
> - if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
> + if (!vma->anon_vma || vma->vm_ops)
> return;
> __vma_adjust_trans_huge(vma, start, end, adjust_next);
> }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 4e43460..72674d4 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -137,7 +137,8 @@ extern unsigned int kobjsize(const void *objp);
> #define VM_RandomReadHint(v) ((v)->vm_flags& VM_RAND_READ)
>
> /*
> - * special vmas that are non-mergable, non-mlock()able
> + * Special vmas that are non-mergable, non-mlock()able.
> + * Note: mm/huge_memory.c VM_NO_THP depends on this definition.
> */
> #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8f76561..56cac93 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1400,6 +1400,9 @@ out:
> return ret;
> }
>
> +#define VM_NO_THP (VM_SPECIAL|VM_INSERTPAGE|VM_MIXEDMAP|VM_SAO| \
> + VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
> +
> int hugepage_madvise(struct vm_area_struct *vma,
> unsigned long *vm_flags, int advice)
> {
> @@ -1408,11 +1411,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
> /*
> * Be somewhat over-protective like KSM for now!
> */
> - if (*vm_flags& (VM_HUGEPAGE |
> - VM_SHARED | VM_MAYSHARE |
> - VM_PFNMAP | VM_IO | VM_DONTEXPAND |
> - VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
> - VM_MIXEDMAP | VM_SAO))
> + if (*vm_flags& (VM_HUGEPAGE | VM_NO_THP))
> return -EINVAL;
> *vm_flags&= ~VM_NOHUGEPAGE;
> *vm_flags |= VM_HUGEPAGE;
> @@ -1428,11 +1427,7 @@ int hugepage_madvise(struct vm_area_struct *vma,
> /*
> * Be somewhat over-protective like KSM for now!
> */
> - if (*vm_flags& (VM_NOHUGEPAGE |
> - VM_SHARED | VM_MAYSHARE |
> - VM_PFNMAP | VM_IO | VM_DONTEXPAND |
> - VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
> - VM_MIXEDMAP | VM_SAO))
> + if (*vm_flags& (VM_NOHUGEPAGE | VM_NO_THP))
> return -EINVAL;
> *vm_flags&= ~VM_HUGEPAGE;
> *vm_flags |= VM_NOHUGEPAGE;
> @@ -1566,10 +1561,14 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
> * page fault if needed.
> */
> return 0;
> - if (vma->vm_file || vma->vm_ops)
> + if (vma->vm_ops)
> /* khugepaged not yet working on file or special mappings */
> return 0;
> - VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma));
> + /*
> + * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
> + * true too, verify it here.
> + */
> + VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags& VM_NO_THP);
> hstart = (vma->vm_start + ~HPAGE_PMD_MASK)& HPAGE_PMD_MASK;
> hend = vma->vm_end& HPAGE_PMD_MASK;
> if (hstart< hend)
> @@ -1818,12 +1817,15 @@ static void collapse_huge_page(struct mm_struct *mm,
> (vma->vm_flags& VM_NOHUGEPAGE))
> goto out;
>
> - /* VM_PFNMAP vmas may have vm_ops null but vm_file set */
> - if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
> + if (!vma->anon_vma || vma->vm_ops)
> goto out;
> if (is_vma_temporary_stack(vma))
> goto out;
> - VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma));
> + /*
> + * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
> + * true too, verify it here.
> + */
> + VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags& VM_NO_THP);
>
> pgd = pgd_offset(mm, address);
> if (!pgd_present(*pgd))
> @@ -2056,13 +2058,16 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
> progress++;
> continue;
> }
> - /* VM_PFNMAP vmas may have vm_ops null but vm_file set */
> - if (!vma->anon_vma || vma->vm_ops || vma->vm_file)
> + if (!vma->anon_vma || vma->vm_ops)
> goto skip;
> if (is_vma_temporary_stack(vma))
> goto skip;
> -
> - VM_BUG_ON(is_linear_pfn_mapping(vma) || is_pfn_mapping(vma));
> + /*
> + * If is_pfn_mapping() is true is_learn_pfn_mapping()
> + * must be true too, verify it here.
> + */
> + VM_BUG_ON(is_linear_pfn_mapping(vma) ||
> + vma->vm_flags& VM_NO_THP);
>
> hstart = (vma->vm_start + ~HPAGE_PMD_MASK)& HPAGE_PMD_MASK;
> hend = vma->vm_end& HPAGE_PMD_MASK;
--
Tim Gardner tim.gardner at canonical.com
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