linux-kernel - [PATCH RFC v2 20/28] ARM: entry: Untangle ret_fast_syscall/to

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Message-Id: <20241029-arm-generic-entry-v2-20-573519abef38@linaro.org>
Date: Tue, 29 Oct 2024 11:53:00 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Oleg Nesterov <oleg@...hat.com>, Russell King <linux@...linux.org.uk>, 
 Kees Cook <kees@...nel.org>, Andy Lutomirski <luto@...capital.net>, 
 Will Drewry <wad@...omium.org>, Frederic Weisbecker <frederic@...nel.org>, 
 "Paul E. McKenney" <paulmck@...nel.org>, 
 Jinjie Ruan <ruanjinjie@...wei.com>, Arnd Bergmann <arnd@...db.de>, 
 Ard Biesheuvel <ardb@...nel.org>, Al Viro <viro@...iv.linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Linus Walleij <linus.walleij@...aro.org>
Subject: [PATCH RFC v2 20/28] ARM: entry: Untangle ret_fast_syscall/to_user

The return to userspace is a bit hard to follow. To prepare
the ground for further refactorings we rewrite the functions
to ret_fast_syscall and ret_to_user are mostly stand-alone
symbols.

Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 arch/arm/kernel/entry-common.S | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index d27e34d7e97a..ece921571714 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -44,20 +44,23 @@ ret_fast_syscall:
 	bl	syscall_exit_to_user_mode
 	ldr	r1, [tsk, #TI_FLAGS]		@ re-check for syscall tracing
 	movs	r1, r1, lsl #16
-	beq	no_work_pending
- UNWIND(.fnend		)
-ENDPROC(ret_fast_syscall)
-
-	/* Slower path - fall through to work_pending */
+	beq	2f

 	tst	r1, #_TIF_SYSCALL_WORK
-	beq	slow_work_pending
+	beq	1f
+
 	b	ret_to_user

-slow_work_pending:
-	mov	r0, sp				@ 'regs'
+1:	mov	r0, sp				@ 'regs'
 	bl	do_work_pending
-	b	no_work_pending
+
+2:	asm_irqentry_exit_to_user_mode
+
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+	bl	stackleak_erase_on_task_stack
+#endif
+	restore_user_regs
+ UNWIND(.fnend		)
 ENDPROC(ret_fast_syscall)

 /*
@@ -74,7 +77,9 @@ ENTRY(ret_to_user)
 ENTRY(ret_to_user_from_irq)
 	ldr	r1, [tsk, #TI_FLAGS]
 	movs	r1, r1, lsl #16
-	bne	slow_work_pending
+	beq	no_work_pending
+	mov	r0, sp				@ 'regs'
+	bl	do_work_pending
 no_work_pending:
 	asm_irqentry_exit_to_user_mode

-- 
2.46.2