Date: Tue, 8 Aug 2017 10:23:48 +0100 From: Mark Rutland <mark.rutland@....com> To: Laura Abbott <labbott@...hat.com> Cc: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org, ard.biesheuvel@...aro.org, catalin.marinas@....com, james.morse@....com, luto@...capital.net, matt@...eblueprint.co.uk, will.deacon@....com, kernel-hardening@...ts.openwall.com, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH] lkdtm: Test VMAP_STACK allocates leading/trailing guard pages 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.
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