On Fri, Jun 09, 2017 at 08:22:26AM +0000, Ard Biesheuvel wrote: > Existing code that uses vmalloc_to_page() may assume that any > address for which is_vmalloc_addr() returns true may be passed > into vmalloc_to_page() to retrieve the associated struct page. > > This is not un unreasonable assumption to make, but on architectures > that have CONFIG_HAVE_ARCH_HUGE_VMAP=y, it no longer holds, and we > need to ensure that vmalloc_to_page() does not go off into the weeds > trying to dereference huge PUDs or PMDs as table entries. > > Given that vmalloc() and vmap() themselves never create huge > mappings or deal with compound pages at all, there is no correct > answer in this case, so return NULL instead, and issue a warning. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > --- > v5: - fix typo > > v4: - use pud_bad/pmd_bad instead of pud_huge/pmd_huge, which don't require > changes to hugetlb.h, and give us what we need on all architectures > - move WARN_ON_ONCE() calls out of conditionals > - add explanatory comment > > mm/vmalloc.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 34a1c3e46ed7..0fcd371266a4 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -287,10 +287,21 @@ struct page *vmalloc_to_page(const void *vmalloc_addr) > if (p4d_none(*p4d)) > return NULL; > pud = pud_offset(p4d, addr); > - if (pud_none(*pud)) > + > + /* > + * Don't dereference bad PUD or PMD (below) entries. This will also > + * identify huge mappings, which we may encounter on architectures > + * that define CONFIG_HAVE_ARCH_HUGE_VMAP=y. Such regions will be > + * identified as vmalloc addresses by is_vmalloc_addr(), but are > + * not [unambiguously] associated with a struct page, so there is > + * no correct value to return for them. > + */ > + WARN_ON_ONCE(pud_bad(*pud)); > + if (pud_none(*pud) || pud_bad(*pud)) > return NULL; Nit: the WARN_ON_ONCE() can be folded into the conditional: if (pud_none(*pud) || WARN_ON_ONCE(pud_bad(*pud))) reutrn NULL; > pmd = pmd_offset(pud, addr); > - if (pmd_none(*pmd)) > + WARN_ON_ONCE(pmd_bad(*pmd)); > + if (pmd_none(*pmd) || pmd_bad(*pmd)) > return NULL; Likewise here. Otherwise, looks good to me. FWIW: Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Thanks, Mark. > > ptep = pte_offset_map(pmd, addr); > -- > 2.9.3 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
