On 9 June 2017 at 09:22, Mark Rutland <mark.rutland@xxxxxxx> wrote: > 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. > Actually, it was Dave who requested them to be taken out of the conditional. > Otherwise, looks good to me. FWIW: > > Acked-by: Mark Rutland <mark.rutland@xxxxxxx> > Thanks, Ard. -- 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>
