[PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers

Marco Elver
2020-08-05T19:59:00Z

Add missing noinstr to arch_local*() helpers, as they may be called from
noinstr code.

On a KCSAN config with CONFIG_PARAVIRT=y, syzbot stumbled across corrupt
IRQ trace state, with lockdep_assert_irqs_enabled() failing spuriously.
When enabling CONFIG_DEBUG_LOCKDEP=y, we get a warning about

DEBUG_LOCKS_WARN_ON(!lockdep_hardirqs_enabled())

which we had seen before due to KCSAN-lockdep recursion. Due to
"lockdep: Prepare for NMI IRQ state tracking", KCSAN was changed to use
non-raw local_irq_{save,restore}(), assuming there is no more
KCSAN-lockdep recursion.

It turns out that the arch_local*() helpers in paravirt.h were missing
noinstr, as they themselves are used from noinstr code that is called
from lockdep. When inserting debug-code that warns us if lockdep is in
the stacktrace from KCSAN, we get,

RIP: 0010:kcsan_setup_watchpoint[...]
[...]
Call Trace:
arch_local_save_flags+0x11/0x30 arch/x86/include/asm/paravirt.h:765
check_preemption_disabled+0x51/0x140 lib/smp_processor_id.c:19
__this_cpu_preempt_check+0x18/0x20 lib/smp_processor_id.c:65
lockdep_hardirqs_off+0xaa/0x130 kernel/locking/lockdep.c:3801
trace_hardirqs_off+0x14/0x80 kernel/trace/trace_preemptirq.c:76
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
_raw_spin_lock_irqsave+0x48/0x90 kernel/locking/spinlock.c:159
wake_up_new_task+0x2c/0x270 kernel/sched/core.c:3338
_do_fork+0x27b/0x4f0 kernel/fork.c:2474
kernel_thread+0x85/0xb0 kernel/fork.c:2502
create_kthread kernel/kthread.c:315 [inline]
kthreadd+0x427/0x500 kernel/kthread.c:634
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

pointing to arch_local_save_flags() in paravirt.h, which is called from
noinstr functions in smp_processor_id.c, which in turn are called from
lockdep.

Link: https://lkml.kernel.org/r/0000000000007d3b2d05ac1c303e@google.com
Reported-by: syzbot+8db9e1ecde74e590a657@syzkaller.appspotmail.com
Signed-off-by: Marco Elver <elver@google.com>
---
arch/x86/include/asm/paravirt.h | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 3d2afecde50c..a606f2ba2b5e 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -760,27 +760,27 @@ bool __raw_callee_save___native_vcpu_is_preempted(long cpu);
((struct paravirt_callee_save) { func })

#ifdef CONFIG_PARAVIRT_XXL
-static inline notrace unsigned long arch_local_save_flags(void)
+static inline noinstr unsigned long arch_local_save_flags(void)
{
return PVOP_CALLEE0(unsigned long, irq.save_fl);
}

-static inline notrace void arch_local_irq_restore(unsigned long f)
+static inline noinstr void arch_local_irq_restore(unsigned long f)
{
PVOP_VCALLEE1(irq.restore_fl, f);
}

-static inline notrace void arch_local_irq_disable(void)
+static inline noinstr void arch_local_irq_disable(void)
{
PVOP_VCALLEE0(irq.irq_disable);
}

-static inline notrace void arch_local_irq_enable(void)
+static inline noinstr void arch_local_irq_enable(void)
{
PVOP_VCALLEE0(irq.irq_enable);
}

-static inline notrace unsigned long arch_local_irq_save(void)
+static inline noinstr unsigned long arch_local_irq_save(void)
{
unsigned long f;

--
2.28.0.163.g6104cc2f0b6-goog