linux-kernel - [PATCH] arm: fix text section corruption

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Message-ID: <1506050119-2670-1-git-send-email-ji.zhang@mediatek.com>
Date:   Fri, 22 Sep 2017 11:15:19 +0800
From:   Ji Zhang <ji.zhang@...iatek.com>
To:     Russell King <linux@...linux.org.uk>,
        Matthias Brugger <matthias.bgg@...il.com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>,
        Ji Zhang <ji.zhang@...iatek.com>
Subject: [PATCH] arm: fix text section corruption

When CONFIG_CPU_SW_DOMAIN_PAN is enabled, there are 9 registers being
pushed into stack in save_regs, but in fixup it still consider there are
8 registers in stack, which is the case of CONFIG_CPU_SW_DOMAIN_PAN
disabled.
When fixup being executed, -EFAULT will be written to the text section.

In fixup:
mov	r4, #-EFAULT
/*
 * When CONFIG_CPU_SW_DOMAIN_PAN enabled, r5 will load the value stored by
 * lr in save_regs, which is the address of instruction in text section.
 */
ldr	r5, [sp,#8*4]	@err_ptr
/*
 * This will write -EFAULT(0xfffffff2) to r5, which points to text section
 * now, and when function returns, it will use 0xfffffff2 as an
 * instruction, then undefined instruction occurs.
 */
str	r4, [r5]

Signed-off-by: Ji Zhang <ji.zhang@...iatek.com>
---
 arch/arm/lib/csumpartialcopyuser.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/lib/csumpartialcopyuser.S b/arch/arm/lib/csumpartialcopyuser.S
index 1712f13..b83fdc0 100644
--- a/arch/arm/lib/csumpartialcopyuser.S
+++ b/arch/arm/lib/csumpartialcopyuser.S
@@ -85,7 +85,11 @@
 		.pushsection .text.fixup,"ax"
 		.align	4
 9001:		mov	r4, #-EFAULT
+#ifdef CONFIG_CPU_SW_DOMAIN_PAN
+		ldr	r5, [sp, #9*4]		@ *err_ptr
+#else
 		ldr	r5, [sp, #8*4]		@ *err_ptr
+#endif
 		str	r4, [r5]
 		ldmia	sp, {r1, r2}		@ retrieve dst, len
 		add	r2, r2, r1
-- 
1.9.1