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

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Date:   Mon, 22 Mar 2021 11:55:08 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Balbir Singh <bsingharora@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, kasan-dev@...glegroups.com,
        christophe.leroy@...roup.eu, aneesh.kumar@...ux.ibm.com
Subject: Re: [PATCH v11 6/6] powerpc: Book3S 64-bit outline-only KASAN support

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.