Commit 3cb5ed4d authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
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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: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201130115950.22492-6-mark.rutland@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 2f911d49

arch/arm64/kernel/entry.S

+5 −4
Original line number Diff line number Diff line
@@ -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)