Commit 985faa78 authored by Mark Rutland's avatar Mark Rutland Committed by Thomas Gleixner
Browse files

powerpc: 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: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Link: https://lore.kernel.org/r/20211129130653.2037928-11-mark.rutland@arm.com
parent 08b0af5b

arch/powerpc/kernel/interrupt.c

+6 −7
Original line number Diff line number Diff line
@@ -181,7 +181,7 @@ 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);
@@ -343,7 +343,7 @@ 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) {
@@ -359,7 +359,7 @@ 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)) {
@@ -437,7 +437,7 @@ 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)))) {
@@ -532,8 +532,7 @@ 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 (regs_is_unrecoverable(regs))

		unrecoverable_exception(regs);
@@ -554,7 +553,7 @@ 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();

			}

arch/powerpc/kernel/ptrace/ptrace.c

+1 −2
Original line number Diff line number Diff line
@@ -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);