linux-kernel - [PATCH v6 06/10] arm64: snapshot thread flags

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Date:   Fri, 22 Oct 2021 14:56:39 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, boqun.feng@...il.com, bp@...en8.de,
        catalin.marinas@....com, dvyukov@...gle.com, elver@...gle.com,
        ink@...assic.park.msu.ru, jonas@...thpole.se,
        juri.lelli@...hat.com, linux@...linux.org.uk, luto@...nel.org,
        mark.rutland@....com, mattst88@...il.com, michal.simek@...inx.com,
        mingo@...hat.com, mpe@...erman.id.au, paulmck@...nel.org,
        paulus@...ba.org, peterz@...radead.org, rth@...ddle.net,
        shorne@...il.com, stefan.kristiansson@...nalahti.fi,
        tglx@...utronix.de, vincent.guittot@...aro.org, will@...nel.org
Subject: [PATCH v6 06/10] arm64: snapshot thread flags

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@....com>
Acked-by: Will Deacon <will@...nel.org>
Acked-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
---
 arch/arm64/kernel/entry-common.c | 2 +-
 arch/arm64/kernel/ptrace.c       | 4 ++--
 arch/arm64/kernel/signal.c       | 2 +-
 arch/arm64/kernel/syscall.c      | 4 ++--
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 32f9796c4ffe..83aef3dd6662 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -128,7 +128,7 @@ static __always_inline void prepare_exit_to_user_mode(struct pt_regs *regs)
 
 	local_daif_mask();
 
-	flags = READ_ONCE(current_thread_info()->flags);
+	flags = read_thread_flags();
 	if (unlikely(flags & _TIF_WORK_MASK))
 		do_notify_resume(regs, flags);
 }
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index e26196a33cf4..9dab4f127cfd 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1839,7 +1839,7 @@ static void tracehook_report_syscall(struct pt_regs *regs,
 
 int syscall_trace_enter(struct pt_regs *regs)
 {
-	unsigned long flags = READ_ONCE(current_thread_info()->flags);
+	unsigned long flags = read_thread_flags();
 
 	if (flags & (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE)) {
 		tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);
@@ -1862,7 +1862,7 @@ int syscall_trace_enter(struct pt_regs *regs)
 
 void syscall_trace_exit(struct pt_regs *regs)
 {
-	unsigned long flags = READ_ONCE(current_thread_info()->flags);
+	unsigned long flags = read_thread_flags();
 
 	audit_syscall_exit(regs);
 
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index c287b9407f28..59f4c1b5d0cf 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -948,7 +948,7 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
 		}
 
 		local_daif_mask();
-		thread_flags = READ_ONCE(current_thread_info()->flags);
+		thread_flags = read_thread_flags();
 	} while (thread_flags & _TIF_WORK_MASK);
 }
 
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 50a0f1a38e84..c938603b3ba0 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -81,7 +81,7 @@ void syscall_trace_exit(struct pt_regs *regs);
 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 			   const syscall_fn_t syscall_table[])
 {
-	unsigned long flags = current_thread_info()->flags;
+	unsigned long flags = read_thread_flags();
 
 	regs->orig_x0 = regs->regs[0];
 	regs->syscallno = scno;
@@ -148,7 +148,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	 */
 	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
 		local_daif_mask();
-		flags = current_thread_info()->flags;
+		flags = read_thread_flags();
 		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
 			return;
 		local_daif_restore(DAIF_PROCCTX);
-- 
2.11.0