linux-kernel - Re: [PATCH v3 5/6] powerpc/fsl_booke/64: clear the original kernel if randomized

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Date:   Wed, 04 Mar 2020 15:53:01 -0600
From:   Scott Wood <oss@...error.net>
To:     Jason Yan <yanaijie@...wei.com>, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com,
        christophe.leroy@....fr, benh@...nel.crashing.org,
        paulus@...ba.org, npiggin@...il.com, keescook@...omium.org,
        kernel-hardening@...ts.openwall.com
Cc:     linux-kernel@...r.kernel.org, zhaohongjiang@...wei.com
Subject: Re: [PATCH v3 5/6] powerpc/fsl_booke/64: clear the original kernel
 if randomized

On Thu, 2020-02-06 at 10:58 +0800, Jason Yan wrote:
> The original kernel still exists in the memory, clear it now.
> 
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> Cc: Scott Wood <oss@...error.net>
> Cc: Diana Craciun <diana.craciun@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe Leroy <christophe.leroy@....fr>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>  arch/powerpc/mm/nohash/kaslr_booke.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/mm/nohash/kaslr_booke.c
> b/arch/powerpc/mm/nohash/kaslr_booke.c
> index c6f5c1db1394..ed1277059368 100644
> --- a/arch/powerpc/mm/nohash/kaslr_booke.c
> +++ b/arch/powerpc/mm/nohash/kaslr_booke.c
> @@ -378,8 +378,10 @@ notrace void __init kaslr_early_init(void *dt_ptr,
> phys_addr_t size)
>  	unsigned int *__kaslr_offset = (unsigned int *)(KERNELBASE + 0x58);
>  	unsigned int *__run_at_load = (unsigned int *)(KERNELBASE + 0x5c);
>  
> -	if (*__run_at_load == 1)
> +	if (*__run_at_load == 1) {
> +		kaslr_late_init();
>  		return;
> +	}

What if you're here because kexec set __run_at_load (or
CONFIG_RELOCATABLE_TEST is enabled), not because kaslr happened?

-Scott