Re: KASAN vs. boot-time switching between 4- and 5-level paging
From: Kirill A. Shutemov
Date: Thu Jul 13 2017 - 09:53:07 EST
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