linux-kernel - Re: [PATCH v11 1/6] kasan: allow an architecture to disable inline instrumentation

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Date:   Sat, 20 Mar 2021 12:46:06 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Daniel Axtens <dja@...ens.net>
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 1/6] kasan: allow an architecture to disable inline
 instrumentation

On Sat, Mar 20, 2021 at 01:40:53AM +1100, Daniel Axtens wrote:
> For annoying architectural reasons, it's very difficult to support inline
> instrumentation on powerpc64.

I think we can expand here and talk about how in hash mode, the vmalloc
address space is in a region of memory different than where kernel virtual
addresses are mapped. Did I recollect the reason correctly?

> 
> Add a Kconfig flag to allow an arch to disable inline. (It's a bit
> annoying to be 'backwards', but I'm not aware of any way to have
> an arch force a symbol to be 'n', rather than 'y'.)
> 
> We also disable stack instrumentation in this case as it does things that
> are functionally equivalent to inline instrumentation, namely adding
> code that touches the shadow directly without going through a C helper.
> 
> Signed-off-by: Daniel Axtens <dja@...ens.net>
> ---
>  lib/Kconfig.kasan | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index cffc2ebbf185..7e237dbb6df3 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -12,6 +12,9 @@ config HAVE_ARCH_KASAN_HW_TAGS
>  config HAVE_ARCH_KASAN_VMALLOC
>  	bool
>  
> +config ARCH_DISABLE_KASAN_INLINE
> +	def_bool n
> +

Some comments on what arch's want to disable kasan inline would
be helpful and why.

Balbir Singh.