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

[Chen Zhongjin]

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 at huawei.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