linux-kernel - [PATCH v4 4/6] powerpc/fsl_booke/64: do not clear the BSS for the second pass

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Message-ID: <20200306064033.3398-5-yanaijie@huawei.com>
Date:   Fri, 6 Mar 2020 14:40:31 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     <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>, <oss@...error.net>
CC:     <linux-kernel@...r.kernel.org>, <zhaohongjiang@...wei.com>,
        <dja@...ens.net>, Jason Yan <yanaijie@...wei.com>
Subject: [PATCH v4 4/6] powerpc/fsl_booke/64: do not clear the BSS for the second pass

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@...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/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 454129a3c259..9354c292b709 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -913,6 +913,13 @@ 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)
+	ld	r3,0(r3)
+	LOAD_REG_IMMEDIATE(r4, KERNELBASE)
+	cmpd	r3,r4
+	bne	4f
+
 	/* Clear out the BSS. It may have been done in prom_init,
 	 * already but that's irrelevant since prom_init will soon
 	 * be detached from the kernel completely. Besides, we need
-- 
2.17.2