Re: [PATCH v11 6/6] powerpc: Book3S 64-bit outline-only KASAN support

Balbir Singh
2021-03-22T02:59:42Z

On Mon, Mar 22, 2021 at 11:55:08AM +1100, Daniel Axtens wrote:
> Hi Balbir,
>
> > Could you highlight the changes from
> > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20170729140901.5887-1-bsingharora@gmail.com/?
> >
> > Feel free to use my signed-off-by if you need to and add/update copyright
> > headers if appropriate.
>
> There's not really anything in common any more:
>
> - ppc32 KASAN landed, so there was already a kasan.h for powerpc, the
> explicit memcpy changes, the support for non-instrumented files,
> prom_check.sh, etc. all already landed.
>
> - I locate the shadow region differently and don't resize any virtual
> memory areas.
>
> - The ARCH_DEFINES_KASAN_ZERO_PTE handling changed upstream and our
> handling for that is now handled more by patch 3.
>
> - The outline hook is now an inline function rather than a #define.
>
> - The init function has been totally rewritten as it's gone from
> supporting real mode to not supporting real mode and back.
>
> - The list of non-instrumented files has grown a lot.
>
> - There's new stuff: stack walking is now safe, KASAN vmalloc support
> means modules are better supported now, ptdump works, and there's
> documentation.
>
> It's been a while now, but I don't think when I started this process 2
> years ago that I directly reused much of your code. So I'm not sure that
> a signed-off-by makes sense here? Would a different tag (Originally-by?)
> make more sense?
>

Sure

> >> + * The shadow ends before the highest accessible address
> >> + * because we don't need a shadow for the shadow. Instead:
> >> + * c00e000000000000 << 3 + a80e 0000 0000 0000 000 = c00fc00000000000
> >
> > The comment has one extra 0 in a80e.., I did the math and had to use
> > the data from the defines :)
>
> 3 extra 0s, even! Fixed.
>
> >> +void __init kasan_init(void)
> >> +{
> >> + /*
> >> + * We want to do the following things:
> >> + * 1) Map real memory into the shadow for all physical memblocks
> >> + * This takes us from c000... to c008...
> >> + * 2) Leave a hole over the shadow of vmalloc space. KASAN_VMALLOC
> >> + * will manage this for us.
> >> + * This takes us from c008... to c00a...
> >> + * 3) Map the 'early shadow'/zero page over iomap and vmemmap space.
> >> + * This takes us up to where we start at c00e...
> >> + */
> >> +
> >
> > assuming we have
> > #define VMEMMAP_END R_VMEMMAP_END
> > and ditto for hash we probably need
> >
> > BUILD_BUG_ON(VMEMMAP_END + KASAN_SHADOW_OFFSET != KASAN_SHADOW_END);
>
> Sorry, I'm not sure what this is supposed to be testing? In what
> situation would this trigger?
>

I am bit concerned that we have hard coded (IIR) 0xa80e... in the
config, any changes to VMEMMAP_END, KASAN_SHADOW_OFFSET/END
should be guarded.

Balbir Singh.