linux-kernel - [PATCH RFC v2 23/28] ARM: entry: Stop exiting syscalls like IRQs

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Message-Id: <20241029-arm-generic-entry-v2-23-573519abef38@linaro.org>
Date: Tue, 29 Oct 2024 11:53:03 +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 23/28] ARM: entry: Stop exiting syscalls like IRQs

The syscalls are issued as software interrupts, and to this point
they were sharing code with the other exception handlers, but
this does not work with generic entry.

Make syscall_exit_to_user_mode do what irqentry_exit_to_user_mode
does at it's tail, and drop the invocations of
irqentry_exit_to_user_mode from the syscall path so that these
are now exception-exclusive.

Split ret_to_user and ret_to_user_from_irq into two distinct
execution paths.

Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 arch/arm/kernel/entry-common.S | 14 ++++++++++++--
 arch/arm/kernel/entry.c        |  4 ++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 5385574c4339..e2ac6d3216b6 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -42,7 +42,6 @@ ret_fast_syscall:
 	/* do_rseq_syscall needs interrupts enabled. */
 	mov	r0, sp				@ 'regs'
 	bl	syscall_exit_to_user_mode
-	asm_irqentry_exit_to_user_mode

 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
 	bl	stackleak_erase_on_task_stack
@@ -62,6 +61,18 @@ ENTRY(ret_to_user)
 	enable_irq_notrace			@ enable interrupts
 	mov	r0, sp				@ 'regs'
 	bl	syscall_exit_to_user_mode
+	ldr	r1, [tsk, #TI_FLAGS]
+	movs	r1, r1, lsl #16
+	beq	1f
+	mov	r0, sp				@ 'regs'
+	bl	do_work_pending
+1:
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+	bl	stackleak_erase_on_task_stack
+#endif
+	restore_user_regs
+ENDPROC(ret_to_user)
+
 ENTRY(ret_to_user_from_irq)
 	ldr	r1, [tsk, #TI_FLAGS]
 	movs	r1, r1, lsl #16
@@ -76,7 +87,6 @@ no_work_pending:
 #endif
 	restore_user_regs
 ENDPROC(ret_to_user_from_irq)
-ENDPROC(ret_to_user)

 /*
  * This is how we return from a fork.
diff --git a/arch/arm/kernel/entry.c b/arch/arm/kernel/entry.c
index 0e3960844b94..88a7a699306a 100644
--- a/arch/arm/kernel/entry.c
+++ b/arch/arm/kernel/entry.c
@@ -30,6 +30,10 @@ void syscall_exit_to_user_mode(struct pt_regs *regs)
 	local_irq_disable();
 	if (has_syscall_work(flags))
 		do_work_pending(regs, flags);
+
+	trace_hardirqs_on();
+	/* This context tracking call has inverse naming */
+	user_enter_callable();
 }

 noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)

-- 
2.46.2