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

Daniel Axtens
2021-03-22T00:55:15Z

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?

>> + * 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?

Kind regards,
Daniel

>
> Looks good otherwise, I've not been able to test it yet
>
> Balbir Singh.