From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 984D26B0279 for ; Fri, 9 Jun 2017 05:22:59 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id t126so24353664pgc.9 for ; Fri, 09 Jun 2017 02:22:59 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id s9si6579766pgn.422.2017.06.09.02.22.58 for ; Fri, 09 Jun 2017 02:22:58 -0700 (PDT) Date: Fri, 9 Jun 2017 10:22:10 +0100 From: Mark Rutland Subject: Re: [PATCH v5] mm: huge-vmap: fail gracefully on unexpected huge vmap mappings Message-ID: <20170609092209.GA10665@leverpostej> References: <20170609082226.26152-1-ard.biesheuvel@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170609082226.26152-1-ard.biesheuvel@linaro.org> Sender: owner-linux-mm@kvack.org List-ID: To: Ard Biesheuvel Cc: linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@suse.com, zhongjiang@huawei.com, labbott@fedoraproject.org, linux-arm-kernel@lists.infradead.org, dave.hansen@intel.com 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 > --- > 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 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org