From 08b0af5b2affbe7419853e8dd1330e4b3fe27125 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 29 Nov 2021 13:06:51 +0000 Subject: powerpc: Avoid discarding flags in system_call_exception() Some thread flags can be set remotely, and so even when IRQs are disabled, the flags can change under our feet. Thus, when setting flags we must use an atomic operation rather than a plain read-modify-write sequence, as a plain read-modify-write may discard flags which are concurrently set by a remote thread, e.g. // task A // task B tmp = A->thread_info.flags; set_tsk_thread_flag(A, NEWFLAG_B); tmp |= NEWFLAG_A; A->thread_info.flags = tmp; arch/powerpc/kernel/interrupt.c's system_call_exception() sets _TIF_RESTOREALL in the thread info flags with a read-modify-write, which may result in other flags being discarded. Elsewhere in the file it uses clear_bits() to atomically remove flag bits, so use set_bits() here for consistency with those. There may be reasons (e.g. instrumentation) that prevent the use of set_thread_flag() and clear_thread_flag() here, which would otherwise be preferable. Fixes: ae7aaecc3f2f78b7 ("powerpc/64s: system call rfscv workaround for TM bugs") Signed-off-by: Mark Rutland Signed-off-by: Thomas Gleixner Cc: Eirik Fuller Cc: Michael Ellerman Cc: Nicholas Piggin Link: https://lore.kernel.org/r/20211129130653.2037928-10-mark.rutland@arm.com --- arch/powerpc/kernel/interrupt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index 835b626cd476..df048e331cbf 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -148,7 +148,7 @@ notrace long system_call_exception(long r3, long r4, long r5, */ if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) && unlikely(MSR_TM_TRANSACTIONAL(regs->msr))) - current_thread_info()->flags |= _TIF_RESTOREALL; + set_bits(_TIF_RESTOREALL, ¤t_thread_info()->flags); /* * If the system call was made with a transaction active, doom it and -- cgit v1.2.3-59-g8ed1b From 985faa78687de6e583cfd8b8094d87dcb80c33a6 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 29 Nov 2021 13:06:52 +0000 Subject: 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: Mark Rutland Signed-off-by: Thomas Gleixner Acked-by: Paul E. McKenney Cc: Benjamin Herrenschmidt Cc: Michael Ellerman Cc: Paul Mackerras Link: https://lore.kernel.org/r/20211129130653.2037928-11-mark.rutland@arm.com --- arch/powerpc/kernel/interrupt.c | 13 ++++++------- arch/powerpc/kernel/ptrace/ptrace.c | 3 +-- 2 files changed, 7 insertions(+), 9 deletions(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index df048e331cbf..563ebfcd16e2 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c @@ -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 @@ again: 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(); } diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c index 7c7093c17c45..c43f77e2ac31 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); -- cgit v1.2.3-59-g8ed1b