Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1032515AbbKEHos (ORCPT ); Thu, 5 Nov 2015 02:44:48 -0500 Received: from mail-ig0-f181.google.com ([209.85.213.181]:37229 "EHLO mail-ig0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032272AbbKEHop (ORCPT ); Thu, 5 Nov 2015 02:44:45 -0500 MIME-Version: 1.0 In-Reply-To: <1446587315-18145-3-git-send-email-labbott@fedoraproject.org> References: <1446587315-18145-1-git-send-email-labbott@fedoraproject.org> <1446587315-18145-3-git-send-email-labbott@fedoraproject.org> Date: Thu, 5 Nov 2015 08:44:44 +0100 Message-ID: Subject: Re: [PATCH 2/2] arm64: Allow changing of attributes outside of modules From: Ard Biesheuvel To: Laura Abbott Cc: Catalin Marinas , Will Deacon , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Kees Cook , Xishi Qiu , Mark Rutland Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3695 Lines: 103 On 3 November 2015 at 22:48, Laura Abbott wrote: > > Currently, the set_memory_* functions that are implemented for arm64 > are restricted to module addresses only. This was mostly done > because arm64 maps normal zone memory with larger page sizes to > improve TLB performance. This has the side effect though of making it > difficult to adjust attributes at the PAGE_SIZE granularity. There are > an increasing number of use cases related to security where it is > necessary to change the attributes of kernel memory. Add functionality > to the page attribute changing code under a Kconfig to let systems > designers decide if they want to make the trade off of security for TLB > pressure. > > Signed-off-by: Laura Abbott > --- > arch/arm64/Kconfig.debug | 11 +++++++ > arch/arm64/mm/mm.h | 3 ++ > arch/arm64/mm/mmu.c | 2 +- > arch/arm64/mm/pageattr.c | 74 ++++++++++++++++++++++++++++++++++++++++++++---- > 4 files changed, 84 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug > index d6285ef..abc6922 100644 > --- a/arch/arm64/Kconfig.debug > +++ b/arch/arm64/Kconfig.debug > @@ -89,6 +89,17 @@ config DEBUG_ALIGN_RODATA > > If in doubt, say N > > +config DEBUG_CHANGE_PAGEATTR I don't think this belongs in Kconfig.debug, and I don't think this should default to off. We know we currently have no users of set_memory_xx() in arch/arm64 that operate on linear mapping addresses, so we will not introduce any performance regressions by adding this functionality now. By putting this feature behind a debug option, every newly introduced call set_memory_xx() that operates on linear or vmalloc() addresses needs to deal with -EINVAL (or depend on DEBUG_CHANGE_PAGEATTR), or it may error out at runtime if the feature is not enabled. > + bool "Allow all kernel memory to have attributes changed" > + help > + If this option is selected, APIs that change page attributes > + (RW <-> RO, X <-> NX) will be valid for all memory mapped in > + the kernel space. The trade off is that there may be increased > + TLB pressure from finer grained page mapping. Turn on this option > + if performance is more important than security > + This is backwards > + If in doubt, say N > + > source "drivers/hwtracing/coresight/Kconfig" > > endmenu [...] > diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c > index e47ed1c..48a4ce9 100644 > --- a/arch/arm64/mm/pageattr.c > +++ b/arch/arm64/mm/pageattr.c [...] > @@ -45,17 +108,18 @@ static int change_memory_common(unsigned long addr, int numpages, > int ret; > struct page_change_data data; > > + if (addr < PAGE_OFFSET && !is_vmalloc_addr((void *)addr)) > + return -EINVAL; > + Doesn't this exclude the module area? > if (!IS_ALIGNED(addr, PAGE_SIZE)) { > start &= PAGE_MASK; > end = start + size; > WARN_ON_ONCE(1); > } > > - if (start < MODULES_VADDR || start >= MODULES_END) > - return -EINVAL; > - > - if (end < MODULES_VADDR || end >= MODULES_END) > - return -EINVAL; > + ret = check_address(addr); > + if (ret) > + return ret; > > data.set_mask = set_mask; > data.clear_mask = clear_mask; > -- > 2.4.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/