From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754819AbbLDBOz (ORCPT ); Thu, 3 Dec 2015 20:14:55 -0500 Received: from mga01.intel.com ([192.55.52.88]:21896 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754780AbbLDBOv (ORCPT ); Thu, 3 Dec 2015 20:14:51 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.20,378,1444719600"; d="scan'208";a="853565055" Subject: [PATCH 19/34] x86, pkeys: optimize fault handling in access_error() To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, x86@kernel.org, Dave Hansen , dave.hansen@linux.intel.com From: Dave Hansen Date: Thu, 03 Dec 2015 17:14:50 -0800 References: <20151204011424.8A36E365@viggo.jf.intel.com> In-Reply-To: <20151204011424.8A36E365@viggo.jf.intel.com> Message-Id: <20151204011450.A07593D5@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen 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. Signed-off-by: Dave Hansen --- b/arch/x86/mm/fault.c | 15 +++++++++++++++ 1 file changed, 15 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 2015-12-03 16:21:26.872727820 -0800 +++ b/arch/x86/mm/fault.c 2015-12-03 16:21:26.876728002 -0800 @@ -900,10 +900,16 @@ bad_area(struct pt_regs *regs, unsigned static inline bool bad_area_access_from_pkeys(unsigned long error_code, struct vm_area_struct *vma) { + /* This code is always called on the current mm */ + int foreign = 0; + if (!boot_cpu_has(X86_FEATURE_OSPKE)) 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), foreign)) + return true; return false; } @@ -1091,6 +1097,8 @@ int show_unhandled_signals = 1; static inline int access_error(unsigned long error_code, struct vm_area_struct *vma) { + /* This is only called for the current mm, so: */ + int foreign = 0; /* * Access or read was blocked by protection keys. We do * this check before any others because we do not want @@ -1099,6 +1107,13 @@ 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), foreign)) + return 1; if (error_code & PF_WRITE) { /* write, present and write, not present: */ _