From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com [209.85.220.44]) by kanga.kvack.org (Postfix) with ESMTP id 85DA86B0274 for ; Wed, 16 Sep 2015 13:56:19 -0400 (EDT) Received: by pacfv12 with SMTP id fv12so219678305pac.2 for ; Wed, 16 Sep 2015 10:56:19 -0700 (PDT) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTP id tc9si42275497pbc.232.2015.09.16.10.49.09 for ; Wed, 16 Sep 2015 10:49:09 -0700 (PDT) Subject: [PATCH 15/26] x86, pkeys: optimize fault handling in access_error() From: Dave Hansen Date: Wed, 16 Sep 2015 10:49:08 -0700 References: <20150916174903.E112E464@viggo.jf.intel.com> In-Reply-To: <20150916174903.E112E464@viggo.jf.intel.com> Message-Id: <20150916174908.01625DF4@viggo.jf.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: dave@sr71.net Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org We might not strictly have to make modifictions to access_error() to check the VMA here. If we do not, we will do this: 1. app sets VMA pkey to K 2. app touches a !present page 3. do_page_fault(), allocates and maps page, sets pte.pkey=K 4. return to userspace 5. touch instruction reexecutes, but triggers PF_PK 6. do PKEY signal What happens with this patch applied: 1. app sets VMA pkey to K 2. app touches a !present page 3. do_page_fault() notices that K is inaccessible 4. do PKEY signal We basically skip the fault that does an allocation. So what this lets us do is protect areas from even being *populated* unless it is accessible according to protection keys. That seems handy to me and makes protection keys work more like an mprotect()'d mapping. --- b/arch/x86/mm/fault.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff -puN arch/x86/mm/fault.c~pkeys-15-access_error arch/x86/mm/fault.c --- a/arch/x86/mm/fault.c~pkeys-15-access_error 2015-09-16 10:48:18.012271934 -0700 +++ b/arch/x86/mm/fault.c 2015-09-16 10:48:18.016272115 -0700 @@ -889,6 +889,9 @@ static inline bool bad_area_access_from_ return false; if (error_code & PF_PK) return true; + /* this checks permission keys on the VMA: */ + if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE))) + return true; return false; } @@ -1075,6 +1078,13 @@ access_error(unsigned long error_code, s */ if (error_code & PF_PK) return 1; + /* + * Make sure to check the VMA so that we do not perform + * faults just to hit a PF_PK as soon as we fill in a + * page. + */ + if (!arch_vma_access_permitted(vma, (error_code & PF_WRITE))) + return 1; if (error_code & PF_WRITE) { /* write, present and write, not present: */ _ -- 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