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Message-ID: <feda5c76f134b415d2f43b99b8d6880b9b4b1750.camel@buserror.net>
From:   Scott Wood <oss@buserror.net>
To:     Jason Yan <yanaijie@huawei.com>, mpe@ellerman.id.au,
        linuxppc-dev@lists.ozlabs.org, diana.craciun@nxp.com,
        christophe.leroy@c-s.fr, benh@kernel.crashing.org,
        paulus@samba.org, npiggin@gmail.com, keescook@chromium.org,
        kernel-hardening@lists.openwall.com
Cc:     linux-kernel@vger.kernel.org, zhaohongjiang@huawei.com
Date:   Wed, 04 Mar 2020 15:49:21 -0600
In-Reply-To: <20200206025825.22934-5-yanaijie@huawei.com>
References: <20200206025825.22934-1-yanaijie@huawei.com>
         <20200206025825.22934-5-yanaijie@huawei.com>
Organization: Red Hat
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Subject: Re: [PATCH v3 4/6] powerpc/fsl_booke/64: do not clear the BSS for
 the second pass
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, 2020-02-06 at 10:58 +0800, Jason Yan wrote:
> The BSS section has already cleared out in the first pass. No need to
> clear it again. This can save some time when booting with KASLR
> enabled.
> 
> Signed-off-by: Jason Yan <yanaijie@huawei.com>
> Cc: Scott Wood <oss@buserror.net>
> Cc: Diana Craciun <diana.craciun@nxp.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Kees Cook <keescook@chromium.org>
> ---
>  arch/powerpc/kernel/head_64.S | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 744624140fb8..8c644e7c3eaf 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -914,6 +914,13 @@ start_here_multiplatform:
>  	bl      relative_toc
>  	tovirt(r2,r2)
>  
> +	/* Do not clear the BSS for the second pass if randomized */
> +	LOAD_REG_ADDR(r3, kernstart_virt_addr)
> +	lwz     r3,0(r3)
> +	LOAD_REG_IMMEDIATE(r4, KERNELBASE)
> +	cmpw	r3,r4
> +	bne	4f

These are 64-bit values.

-Scott