linux-kernel - [PATCH v6 30/33] arm64: entry: Align stack size for alternative

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Date:   Thu, 23 Jun 2022 09:49:14 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
        <linuxppc-dev@...ts.ozlabs.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kbuild@...r.kernel.org>, <live-patching@...r.kernel.org>
CC:     <jpoimboe@...nel.org>, <peterz@...radead.org>,
        <catalin.marinas@....com>, <will@...nel.org>,
        <masahiroy@...nel.org>, <michal.lkml@...kovi.net>,
        <ndesaulniers@...gle.com>, <mark.rutland@....com>,
        <pasha.tatashin@...een.com>, <broonie@...nel.org>,
        <chenzhongjin@...wei.com>, <rmk+kernel@...linux.org.uk>,
        <madvenka@...ux.microsoft.com>, <christophe.leroy@...roup.eu>,
        <daniel.thompson@...aro.org>
Subject: [PATCH v6 30/33] 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 d49bfbe81a0d..677e3be471bb 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -430,7 +430,11 @@ 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
@@ -729,6 +733,7 @@ alternative_else_nop_endif
 
 	.macro tramp_exit, regsize = 64
 	UNWIND_HINT_EMPTY
+	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