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From: Mark Rutland <mark.rutland@arm.com>
To: linux-kernel@vger.kernel.org
Cc: benh@kernel.crashing.org, boqun.feng@gmail.com, bp@alien8.de,
	catalin.marinas@arm.com, dvyukov@google.com, elver@google.com,
	ink@jurassic.park.msu.ru, jonas@southpole.se,
	juri.lelli@redhat.com, linux@armlinux.org.uk, luto@kernel.org,
	mark.rutland@arm.com, mattst88@gmail.com, mingo@redhat.com,
	monstr@monstr.eu, mpe@ellerman.id.au, paulmck@kernel.org,
	paulus@samba.org, peterz@infradead.org, rth@twiddle.net,
	shorne@gmail.com, stefan.kristiansson@saunalahti.fi,
	tglx@linutronix.de, vincent.guittot@linaro.org, will@kernel.org
Subject: [PATCH v4 09/10] powerpc: snapshot thread flags
Date: Tue,  3 Aug 2021 10:54:27 +0100	[thread overview]
Message-ID: <20210803095428.17009-10-mark.rutland@arm.com> (raw)
In-Reply-To: <20210803095428.17009-1-mark.rutland@arm.com>

Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/kernel/interrupt.c     | 13 ++++++-------
 arch/powerpc/kernel/ptrace/ptrace.c |  3 +--
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 21bbd615ca41..850369c1e73e 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -140,7 +140,7 @@ notrace long system_call_exception(long r3, long r4, long r5,
 
 	local_irq_enable();
 
-	if (unlikely(current_thread_info()->flags & _TIF_SYSCALL_DOTRACE)) {
+	if (unlikely(read_thread_flags() & _TIF_SYSCALL_DOTRACE)) {
 		if (unlikely(trap_is_unsupported_scv(regs))) {
 			/* Unsupported scv vector */
 			_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
@@ -302,7 +302,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
 	unsigned long ti_flags;
 
 again:
-	ti_flags = READ_ONCE(current_thread_info()->flags);
+	ti_flags = read_thread_flags();
 	while (unlikely(ti_flags & (_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM))) {
 		local_irq_enable();
 		if (ti_flags & _TIF_NEED_RESCHED) {
@@ -318,7 +318,7 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)
 			do_notify_resume(regs, ti_flags);
 		}
 		local_irq_disable();
-		ti_flags = READ_ONCE(current_thread_info()->flags);
+		ti_flags = read_thread_flags();
 	}
 
 	if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && IS_ENABLED(CONFIG_PPC_FPU)) {
@@ -396,7 +396,7 @@ notrace unsigned long syscall_exit_prepare(unsigned long r3,
 	/* Check whether the syscall is issued inside a restartable sequence */
 	rseq_syscall(regs);
 
-	ti_flags = current_thread_info()->flags;
+	ti_flags = read_thread_flags();
 
 	if (unlikely(r3 >= (unsigned long)-MAX_ERRNO) && is_not_scv) {
 		if (likely(!(ti_flags & (_TIF_NOERROR | _TIF_RESTOREALL)))) {
@@ -493,8 +493,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 	unsigned long flags;
 	unsigned long ret = 0;
 	unsigned long kuap;
-	bool stack_store = current_thread_info()->flags &
-						_TIF_EMULATE_STACK_STORE;
+	bool stack_store = read_thread_flags() & _TIF_EMULATE_STACK_STORE;
 
 	if (!IS_ENABLED(CONFIG_BOOKE) && !IS_ENABLED(CONFIG_40x) &&
 	    unlikely(!(regs->msr & MSR_RI)))
@@ -517,7 +516,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
 again:
 		if (IS_ENABLED(CONFIG_PREEMPT)) {
 			/* Return to preemptible kernel context */
-			if (unlikely(current_thread_info()->flags & _TIF_NEED_RESCHED)) {
+			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
 				if (preempt_count() == 0)
 					preempt_schedule_irq();
 			}
diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
index 0a0a33eb0d28..d174570a144e 100644
--- a/arch/powerpc/kernel/ptrace/ptrace.c
+++ b/arch/powerpc/kernel/ptrace/ptrace.c
@@ -260,8 +260,7 @@ long do_syscall_trace_enter(struct pt_regs *regs)
 {
 	u32 flags;
 
-	flags = READ_ONCE(current_thread_info()->flags) &
-		(_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
+	flags = read_thread_flags() & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
 
 	if (flags) {
 		int rc = tracehook_report_syscall_entry(regs);
-- 
2.11.0


  parent reply	other threads:[~2021-08-03  9:56 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03  9:54 [PATCH v4 00/10] thread_info: use helpers to " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 01/10] thread_info: add " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 02/10] entry: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 03/10] sched: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 04/10] alpha: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 05/10] arm: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 06/10] arm64: " Mark Rutland
2021-08-03  9:54 ` [PATCH v4 07/10] microblaze: " Mark Rutland
2021-08-25  9:03   ` Michal Simek
2021-08-03  9:54 ` [PATCH v4 08/10] openrisc: " Mark Rutland
2021-08-03  9:54 ` Mark Rutland [this message]
2021-08-03  9:54 ` [PATCH v4 10/10] x86: " Mark Rutland
2021-08-03 16:01 ` [PATCH v4 00/10] thread_info: use helpers to " Paul E. McKenney

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