Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752113AbdHHJZC (ORCPT ); Tue, 8 Aug 2017 05:25:02 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:58604 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750818AbdHHJZB (ORCPT ); Tue, 8 Aug 2017 05:25:01 -0400 Date: Tue, 8 Aug 2017 10:23:48 +0100 From: Mark Rutland To: Laura Abbott Cc: Kees Cook , linux-kernel@vger.kernel.org, ard.biesheuvel@linaro.org, catalin.marinas@arm.com, james.morse@arm.com, luto@amacapital.net, matt@codeblueprint.co.uk, will.deacon@arm.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] lkdtm: Test VMAP_STACK allocates leading/trailing guard pages Message-ID: <20170808092348.GA19207@leverpostej> References: <20170807203948.GA22298@beast> <20170807220056.GA29059@remoulade> <0e9a80c2-3e5e-db98-dff6-b45e9e4817fd@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0e9a80c2-3e5e-db98-dff6-b45e9e4817fd@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2138 Lines: 42 On Mon, Aug 07, 2017 at 03:55:22PM -0700, Laura Abbott wrote: > On 08/07/2017 03:00 PM, Mark Rutland wrote: > > On Mon, Aug 07, 2017 at 01:39:48PM -0700, Kees Cook wrote: > >> Do these tests both trip with the new arm64 VMAP_STACK code? > > > >> +/* Test that VMAP_STACK is actually allocating with a leading guard page */ > >> +void lkdtm_STACK_GUARD_PAGE_LEADING(void) > >> +/* Test that VMAP_STACK is actually allocating with a trailing guard page */ > >> +void lkdtm_STACK_GUARD_PAGE_TRAILING(void) > > I can give these a go tomorrow. > > > > These *should* fault, and IIUC should trigger the usual "Unable to handle > > kernel %s at virtual address %08lx\n" splat from arm64's __do_kernel_fault(), > > which should end up with an Oops(). > I gave these a quick test in QEMU and they seem to do the correct thing: > # echo STACK_GUARD_PAGE_LEADING > /sys/kernel/debug/provoke-crash/DIRECT > [ 24.593306] lkdtm: Performing direct entry STACK_GUARD_PAGE_LEADING > [ 24.593780] lkdtm: attempting bad read from page below current stack > [ 24.594289] Unable to handle kernel paging request at virtual address ffff000009b77fff > [ 24.594747] swapper pgtable: 4k pages, 48-bit VAs, pgd = ffff000009050000 > [ 24.595443] [ffff000009b77fff] *pgd=000000007effe003, *pud=000000007effd003, *pmd=000000007cc43003, *pte=0000000000000000 > [ 24.596743] Internal error: Oops: 96000007 [#1] PREEMPT SMP > # echo STACK_GUARD_PAGE_TRAILING > /sys/kernel/debug/provoke-crash/DIRECT > [ 103.144313] lkdtm: Performing direct entry STACK_GUARD_PAGE_TRAILING > [ 103.144749] lkdtm: attempting bad read from page above current stack > [ 103.145100] Unable to handle kernel paging request at virtual address ffff000009c2c000 > [ 103.145477] swapper pgtable: 4k pages, 48-bit VAs, pgd = ffff000009050000 > [ 103.145836] [ffff000009c2c000] *pgd=000000007effe003, *pud=000000007effd003, *pmd=000000007d014003, *pte=0000000000000000 > [ 103.146445] Internal error: Oops: 96000007 [#2] PREEMPT SMP Great! thanks for giving those a spin. I can confirm likewise on Juno with 64K pages (not that this should make any difference). Mark.