From 3cb5ed4d76c15fb97c10e5e9f5268d92c68222ca Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 30 Nov 2020 11:59:44 +0000 Subject: [PATCH] arm64: entry: prepare ret_to_user for function call In a subsequent patch ret_to_user will need to make a C function call (in some configurations) which may clobber x0-x18 at the start of the finish_ret_to_user block, before enable_step_tsk consumes the flags loaded into x1. In preparation for this, let's load the flags into x19, which is preserved across C function calls. This avoids a redundant reload of the flags and ensures we operate on a consistent shapshot regardless. There should be no functional change as a result of this patch. At this point of the entry/exit paths we only need to preserve x28 (tsk) and the sp, and x19 is free for this use. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: James Morse Cc: Will Deacon Link: https://lore.kernel.org/r/20201130115950.22492-6-mark.rutland@arm.com Signed-off-by: Will Deacon --- arch/arm64/kernel/entry.S | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index b295fb912b12b2..84aec600eeed4c 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -774,13 +774,13 @@ SYM_CODE_END(el0_error) SYM_CODE_START_LOCAL(ret_to_user) disable_daif gic_prio_kentry_setup tmp=x3 - ldr x1, [tsk, #TSK_TI_FLAGS] - and x2, x1, #_TIF_WORK_MASK + ldr x19, [tsk, #TSK_TI_FLAGS] + and x2, x19, #_TIF_WORK_MASK cbnz x2, work_pending finish_ret_to_user: /* Ignore asynchronous tag check faults in the uaccess routines */ clear_mte_async_tcf - enable_step_tsk x1, x2 + enable_step_tsk x19, x2 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK bl stackleak_erase #endif @@ -791,11 +791,12 @@ finish_ret_to_user: */ work_pending: mov x0, sp // 'regs' + mov x1, x19 bl do_notify_resume #ifdef CONFIG_TRACE_IRQFLAGS bl trace_hardirqs_on // enabled while in userspace #endif - ldr x1, [tsk, #TSK_TI_FLAGS] // re-check for single-step + ldr x19, [tsk, #TSK_TI_FLAGS] // re-check for single-step b finish_ret_to_user SYM_CODE_END(ret_to_user)