linux-kernel - [PATCH RFC v2 17/28] ARM: entry: Implement syscall_exit_to_user

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Message-Id: <20241029-arm-generic-entry-v2-17-573519abef38@linaro.org>
Date: Tue, 29 Oct 2024 11:52:57 +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 17/28] ARM: entry: Implement
 syscall_exit_to_user_mode()

Mirroring syscall_enter_from_user_mode() we create the sibling
call syscall_exit_to_user_mode() and start to move some stuff
over from assembly, first the rseq call and the interrupt
disablement.

Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
---
 arch/arm/include/asm/entry.h   |  1 +
 arch/arm/include/asm/signal.h  |  1 -
 arch/arm/kernel/entry-common.S | 10 ++--------
 arch/arm/kernel/entry.c        |  8 ++++++++
 arch/arm/kernel/signal.c       |  7 -------
 5 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/arch/arm/include/asm/entry.h b/arch/arm/include/asm/entry.h
index e259b074caef..8b8cc9a1eefb 100644
--- a/arch/arm/include/asm/entry.h
+++ b/arch/arm/include/asm/entry.h
@@ -9,6 +9,7 @@ struct pt_regs;
  * to generic entry once they are semantically equivalent.
  */
 long syscall_enter_from_user_mode(struct pt_regs *regs, long);
+void syscall_exit_to_user_mode(struct pt_regs *regs);
 void irqentry_enter_from_user_mode(struct pt_regs *regs);
 void irqentry_exit_to_user_mode(struct pt_regs *regs);
 
diff --git a/arch/arm/include/asm/signal.h b/arch/arm/include/asm/signal.h
index 7acccc96840c..bb753cd3e29f 100644
--- a/arch/arm/include/asm/signal.h
+++ b/arch/arm/include/asm/signal.h
@@ -23,7 +23,6 @@ typedef struct {
 
 #include <asm/sigcontext.h>
 
-void do_rseq_syscall(struct pt_regs *regs);
 void do_work_pending(struct pt_regs *regs, unsigned int thread_flags);
 
 #endif
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index df564388905e..3559e0a9f5e0 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -65,12 +65,9 @@ ret_fast_syscall:
  UNWIND(.fnstart	)
  UNWIND(.cantunwind	)
 	add	sp, sp, #(S_R0 + S_OFF)
-#if IS_ENABLED(CONFIG_DEBUG_RSEQ)
 	/* do_rseq_syscall needs interrupts enabled. */
 	mov	r0, sp				@ 'regs'
-	bl	do_rseq_syscall
-#endif
-	disable_irq_notrace			@ disable interrupts
+	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
@@ -97,13 +94,10 @@ ENDPROC(ret_fast_syscall)
  * do_work_pending() will update this state if necessary.
  */
 ENTRY(ret_to_user)
-#if IS_ENABLED(CONFIG_DEBUG_RSEQ)
 	/* do_rseq_syscall needs interrupts enabled. */
 	enable_irq_notrace			@ enable interrupts
 	mov	r0, sp				@ 'regs'
-	bl	do_rseq_syscall
-#endif
-	disable_irq_notrace			@ disable interrupts
+	bl	syscall_exit_to_user_mode
 ENTRY(ret_to_user_from_irq)
 	ldr	r1, [tsk, #TI_FLAGS]
 	movs	r1, r1, lsl #16
diff --git a/arch/arm/kernel/entry.c b/arch/arm/kernel/entry.c
index 1973947c7ad7..472338047337 100644
--- a/arch/arm/kernel/entry.c
+++ b/arch/arm/kernel/entry.c
@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <asm/entry.h>
+#include <asm/signal.h>
 #include <linux/context_tracking.h>
 #include <linux/irqflags.h>
+#include <linux/rseq.h>
 
 long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
 {
@@ -14,6 +16,12 @@ long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
 	return syscall;
 }
 
+void syscall_exit_to_user_mode(struct pt_regs *regs)
+{
+	rseq_syscall(regs);
+	local_irq_disable();
+}
+
 noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
 {
 	trace_hardirqs_off();
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 7b1a16e86b23..03b20637a2e1 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -659,13 +659,6 @@ struct page *get_signal_page(void)
 	return page;
 }
 
-#ifdef CONFIG_DEBUG_RSEQ
-asmlinkage void do_rseq_syscall(struct pt_regs *regs)
-{
-	rseq_syscall(regs);
-}
-#endif
-
 /*
  * Compile-time assertions for siginfo_t offsets. Check NSIG* as well, as
  * changes likely come with new fields that should be added below.

-- 
2.46.2