linux-kernel - [RFC PATCH v4 36/37] arm64: entry: Align stack size for alternative

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Date:   Fri, 29 Apr 2022 17:43:54 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-arch@...r.kernel.org>
CC:     <jthierry@...hat.com>, <catalin.marinas@....com>,
        <will@...nel.org>, <masahiroy@...nel.org>, <jpoimboe@...hat.com>,
        <peterz@...radead.org>, <ycote@...hat.com>,
        <herbert@...dor.apana.org.au>, <mark.rutland@....com>,
        <davem@...emloft.net>, <ardb@...nel.org>, <maz@...nel.org>,
        <tglx@...utronix.de>, <luc.vanoostenryck@...il.com>,
        <chenzhongjin@...wei.com>
Subject: [RFC PATCH v4 36/37] arm64: entry: Align stack size for alternative

In kernel_exit there is a alternative branch for KPTI which causes
stack size conflict for two instruction boundaries.

To fix that, make both branch move the sp and then revert it in
tramp_exit branch.

Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
---
 arch/arm64/kernel/entry.S | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c7ab5143949f..fa3c5a2cd2c3 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -429,7 +429,11 @@ alternative_if_not ARM64_UNMAP_KERNEL_AT_EL0
 	ldr	lr, [sp, #S_LR]
 	add	sp, sp, #PT_REGS_SIZE		// restore sp
 	eret
-alternative_else_nop_endif
+alternative_else
+	nop
+	add sp, sp, #PT_REGS_SIZE       // restore sp
+	nop
+alternative_endif
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 	bne	4f
 	msr	far_el1, x29
@@ -726,6 +730,7 @@ alternative_else_nop_endif
 	.endm
 
 	.macro tramp_exit, regsize = 64
+	sub sp, sp, #PT_REGS_SIZE       // revert sp
 	tramp_data_read_var	x30, this_cpu_vector
 	get_this_cpu_offset x29
 	ldr	x30, [x30, x29]
-- 
2.17.1