On Thu, Jun 08, 2017 at 11:35:48AM +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 > value to return in this case, so return NULL instead, and issue a > warning. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > --- > This is a followup to '[PATCH v2] mm: vmalloc: make vmalloc_to_page() > deal with PMD/PUD mappings', hence the v3. The root issue with /proc/kcore > on arm64 is now handled by '[PATCH] mm: vmalloc: simplify vread/vwrite to > use existing mappings' [1], and this patch now only complements it by > taking care of other vmalloc_to_page() users. > > [0] http://marc.info/?l=linux-mm&m=149641886821855&w=2 > [1] http://marc.info/?l=linux-mm&m=149685966530180&w=2 > > include/linux/hugetlb.h | 13 +++++++++---- > mm/vmalloc.c | 5 +++-- > 2 files changed, 12 insertions(+), 6 deletions(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index b857fc8cc2ec..b7166e5426b6 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -121,8 +121,6 @@ struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address, > pmd_t *pmd, int flags); > struct page *follow_huge_pud(struct mm_struct *mm, unsigned long address, > pud_t *pud, int flags); > -int pmd_huge(pmd_t pmd); > -int pud_huge(pud_t pud); > unsigned long hugetlb_change_protection(struct vm_area_struct *vma, > unsigned long address, unsigned long end, pgprot_t newprot); > > @@ -150,8 +148,6 @@ static inline void hugetlb_show_meminfo(void) > #define follow_huge_pmd(mm, addr, pmd, flags) NULL > #define follow_huge_pud(mm, addr, pud, flags) NULL > #define prepare_hugepage_range(file, addr, len) (-EINVAL) > -#define pmd_huge(x) 0 > -#define pud_huge(x) 0 > #define is_hugepage_only_range(mm, addr, len) 0 > #define hugetlb_free_pgd_range(tlb, addr, end, floor, ceiling) ({BUG(); 0; }) > #define hugetlb_fault(mm, vma, addr, flags) ({ BUG(); 0; }) > @@ -190,6 +186,15 @@ static inline void __unmap_hugepage_range(struct mmu_gather *tlb, > } > > #endif /* !CONFIG_HUGETLB_PAGE */ > + > +#if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_HAVE_ARCH_HUGE_VMAP) > +int pmd_huge(pmd_t pmd); > +int pud_huge(pud_t pud); > +#else > +#define pmd_huge(x) 0 > +#define pud_huge(x) 0 > +#endif > + > /* > * hugepages at page global directory. If arch support > * hugepages at pgd level, they need to define this. > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 982d29511f92..67e1a304c467 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -12,6 +12,7 @@ > #include <linux/mm.h> > #include <linux/module.h> > #include <linux/highmem.h> > +#include <linux/hugetlb.h> > #include <linux/sched/signal.h> > #include <linux/slab.h> > #include <linux/spinlock.h> > @@ -287,10 +288,10 @@ struct page *vmalloc_to_page(const void *vmalloc_addr) > if (p4d_none(*p4d)) > return NULL; > pud = pud_offset(p4d, addr); > - if (pud_none(*pud)) > + if (pud_none(*pud) || WARN_ON_ONCE(pud_huge(*pud))) > return NULL; > pmd = pmd_offset(pud, addr); > - if (pmd_none(*pmd)) > + if (pmd_none(*pmd) || WARN_ON_ONCE(pmd_huge(*pmd))) > return NULL; I think it might be better to use p*d_bad() here, since that doesn't depend on CONFIG_HUGETLB_PAGE. While the cross-arch semantics are a little fuzzy, my understanding is those should return true if an entry is not a pointer to a next level of table (so pXd_huge(p) implies pXd_bad(p)). Otherwise, this looks sensible to me. Thanks, Mark. -- 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>
