linux-kernel - Re: KASAN vs. boot-time switching between 4- and 5-level paging

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Message-ID: <20170713135228.vhvpe7mqdcqzpslw@node.shutemov.name>
Date:   Thu, 13 Jul 2017 16:52:28 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: KASAN vs. boot-time switching between 4- and 5-level paging

On Thu, Jul 13, 2017 at 03:58:29PM +0300, Andrey Ryabinin wrote:
> On 07/11/2017 10:05 PM, Kirill A. Shutemov wrote:
> >>> Can use your Signed-off-by for a [cleaned up version of your] patch?
> >>
> >> Sure.
> > 
> > Another KASAN-releated issue: dumping page tables for KASAN shadow memory
> > region takes unreasonable time due to kasan_zero_p?? mapped there.
> > 
> > The patch below helps. Any objections?
> > 
> 
> Well, page tables dump doesn't work at all on 5-level paging.
> E.g. I've got this nonsense: 
> 
> ....
> ---[ Kernel Space ]---
> 0xffff800000000000-0xffff808000000000         512G                               pud
> ---[ Low Kernel Mapping ]---
> 0xffff808000000000-0xffff810000000000         512G                               pud
> ---[ vmalloc() Area ]---
> 0xffff810000000000-0xffff818000000000         512G                               pud
> ---[ Vmemmap ]---
> 0xffff818000000000-0xffffff0000000000      128512G                               pud
> ---[ ESPfix Area ]---
> 0xffffff0000000000-0x0000000000000000           1T                               pud
> 0x0000000000000000-0x0000000000000000           0E                               pgd
> 0x0000000000000000-0x0000000000001000           4K     RW     PCD         GLB NX pte
> 0x0000000000001000-0x0000000000002000           4K                               pte
> 0x0000000000002000-0x0000000000003000           4K     ro                 GLB NX pte
> 0x0000000000003000-0x0000000000004000           4K                               pte
> 0x0000000000004000-0x0000000000007000          12K     RW                 GLB NX pte
> 0x0000000000007000-0x0000000000008000           4K                               pte
> 0x0000000000008000-0x0000000000108000           1M     RW                 GLB NX pte
> 0x0000000000108000-0x0000000000109000           4K                               pte
> 0x0000000000109000-0x0000000000189000         512K     RW                 GLB NX pte
> 0x0000000000189000-0x000000000018a000           4K                               pte
> 0x000000000018a000-0x000000000018e000          16K     RW                 GLB NX pte
> 0x000000000018e000-0x000000000018f000           4K                               pte
> 0x000000000018f000-0x0000000000193000          16K     RW                 GLB NX pte
> 0x0000000000193000-0x0000000000194000           4K                               pte
> ... 304 entries skipped ... 
> ---[ EFI Runtime Services ]---
> 0xffffffef00000000-0xffffffff80000000          66G                               pud
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffffc0000000           1G                               pud
> ...

Hm. I don't see this:

...
[    0.247532] 0xff9e938000000000-0xff9f000000000000      111104G                               p4d
[    0.247733] 0xff9f000000000000-0xffff000000000000          24P                               pgd
[    0.248066] 0xffff000000000000-0xffffff0000000000         255T                               p4d
[    0.248290] ---[ ESPfix Area ]---
[    0.248393] 0xffffff0000000000-0xffffff8000000000         512G                               p4d
[    0.248663] 0xffffff8000000000-0xffffffef00000000         444G                               pud
[    0.248892] ---[ EFI Runtime Services ]---
[    0.248996] 0xffffffef00000000-0xfffffffec0000000          63G                               pud
[    0.249308] 0xfffffffec0000000-0xfffffffefe400000         996M                               pmd
...

Do you have commit "x86/dump_pagetables: Generalize address normalization"
in your tree?

https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/commit/?h=la57/boot-switching/v2&id=13327fec85ffe95d9c8a3f57ba174bf5d5c1fb01

> As for KASAN, I think it would be better just to make it work faster,
> the patch below demonstrates the idea.

Okay, let me test this.

> ---
>  arch/x86/mm/dump_pagetables.c | 22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
> index 0470826d2bdc..36515fba86b0 100644
> --- a/arch/x86/mm/dump_pagetables.c
> +++ b/arch/x86/mm/dump_pagetables.c
> @@ -13,6 +13,7 @@
>   */
>  
>  #include <linux/debugfs.h>
> +#include <linux/kasan.h>
>  #include <linux/mm.h>
>  #include <linux/init.h>
>  #include <linux/sched.h>

<asm/kasan.h> can be dropped. And I don't think it compiles with KASAN
disabled.

For reference, the patch I use now:

https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/commit/?h=la57/boot-switching/v2&id=c4b1439f719b1689a1cfca9c0df17b9f8b8462b9

-- 
 Kirill A. Shutemov