linux-kernel - [RFC PATCH for 4.18 04/16] arm: Add syscall detection for restartable sequences

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Date:   Sat,  2 Jun 2018 08:43:56 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH for 4.18 04/16] arm: Add syscall detection for restartable sequences

Syscalls are not allowed inside restartable sequences, so add a call to
rseq_syscall() at the very beginning of system call exiting path for
CONFIG_DEBUG_RSEQ=y kernel. This could help us to detect whether there
is a syscall issued inside restartable sequences.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC: Russell King <linux@....linux.org.uk>
CC: Catalin Marinas <catalin.marinas@....com>
CC: Will Deacon <will.deacon@....com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Paul Turner <pjt@...gle.com>
CC: Andrew Hunter <ahh@...gle.com>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Andy Lutomirski <luto@...capital.net>
CC: Andi Kleen <andi@...stfloor.org>
CC: Dave Watson <davejwatson@...com>
CC: Chris Lameter <cl@...ux.com>
CC: Ingo Molnar <mingo@...hat.com>
CC: Ben Maurer <bmaurer@...com>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC: Josh Triplett <josh@...htriplett.org>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Boqun Feng <boqun.feng@...il.com>
CC: linux-api@...r.kernel.org
---
 arch/arm/kernel/entry-common.S | 25 +++++++++++++++++++------
 arch/arm/kernel/signal.c       |  7 +++++++
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 3c4f88701f22..b427ef8ec8c6 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -39,12 +39,13 @@ saved_pc	.req	lr
 
 	.section .entry.text,"ax",%progbits
 	.align	5
-#if !(IS_ENABLED(CONFIG_TRACE_IRQFLAGS) || IS_ENABLED(CONFIG_CONTEXT_TRACKING))
+#if !(IS_ENABLED(CONFIG_TRACE_IRQFLAGS) || IS_ENABLED(CONFIG_CONTEXT_TRACKING) || \
+	IS_ENABLED(CONFIG_DEBUG_RSEQ))
 /*
  * This is the fast syscall return path.  We do as little as possible here,
  * such as avoiding writing r0 to the stack.  We only use this path if we
- * have tracing and context tracking disabled - the overheads from those
- * features make this path too inefficient.
+ * have tracing, context tracking and rseq debug disabled - the overheads
+ * from those features make this path too inefficient.
  */
 ret_fast_syscall:
  UNWIND(.fnstart	)
@@ -71,14 +72,20 @@ fast_work_pending:
 	/* fall through to work_pending */
 #else
 /*
- * The "replacement" ret_fast_syscall for when tracing or context tracking
- * is enabled.  As we will need to call out to some C functions, we save
- * r0 first to avoid needing to save registers around each C function call.
+ * The "replacement" ret_fast_syscall for when tracing, context tracking,
+ * or rseq debug is enabled.  As we will need to call out to some C functions,
+ * we save r0 first to avoid needing to save registers around each C function
+ * call.
  */
 ret_fast_syscall:
  UNWIND(.fnstart	)
  UNWIND(.cantunwind	)
 	str	r0, [sp, #S_R0 + S_OFF]!	@ save returned r0
+#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
 	ldr	r2, [tsk, #TI_ADDR_LIMIT]
 	cmp	r2, #TASK_SIZE
@@ -113,6 +120,12 @@ ENDPROC(ret_fast_syscall)
  */
 ENTRY(ret_to_user)
 ret_slow_syscall:
+#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
 ENTRY(ret_to_user_from_irq)
 	ldr	r2, [tsk, #TI_ADDR_LIMIT]
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 5879ab3f53c1..f09e9d66d605 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -710,3 +710,10 @@ asmlinkage void addr_limit_check_failed(void)
 {
 	addr_limit_user_check();
 }
+
+#ifdef CONFIG_DEBUG_RSEQ
+asmlinkage void do_rseq_syscall(struct pt_regs *regs)
+{
+	rseq_syscall(regs);
+}
+#endif
-- 
2.11.0