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Message-Id: <20241029-arm-generic-entry-v2-21-573519abef38@linaro.org>
Date: Tue, 29 Oct 2024 11:53:01 +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 21/28] 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 ece921571714..33bc9e7c5b32 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
--
2.46.2
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