linux-kernel - [PATCH RFC v3 21/30] ARM: entry: Do not double-call exit functions

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Message-Id: <20250107-arm-generic-entry-v3-21-4e5f3c15db2d@linaro.org>
Date: Tue, 07 Jan 2025 10:41:37 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Dmitry Vyukov <dvyukov@...gle.com>, 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 v3 21/30] ARM: entry: Do not double-call exit functions

This is a semantic change to ret_fast_syscall: if there is no
work pending the function used to jump to ret_to_user, instead
we proceed to return from the syscall.

If we jump to ret_to_user, IRQs are enabled and we call
syscall_exit_to_user_mode a second time; at this point a
this just means a second call to rseq_syscall(), but it
seems wrong and we want syscall_exit_to_user_mode to be called
exactly once.

Apparently the ARM kernel has under some circumstances called
rseq_syscall() twice on the exit to userspace without side effects.

ret_to_user also checks for pending work a second time under
ret_to_user_from_irq, but this isn't even needed any more on
the fast return path: this was needed because the syscall
invocation enabled interrupts when doing syscall tracing, and
all tracing invocation has been moved over to C in earlier
patches.

Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 arch/arm/kernel/entry-common.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index ece9215717143427de7572a18a6dbe620a9193e9..33bc9e7c5b32f62474724f1d47f97af24dba53bf 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -49,7 +49,7 @@ ret_fast_syscall:
 	tst	r1, #_TIF_SYSCALL_WORK
 	beq	1f

-	b	ret_to_user
+	b	2f

 1:	mov	r0, sp				@ 'regs'
 	bl	do_work_pending

-- 
2.47.1