kcov: properly check if we are in an interrupt

in_interrupt() returns a nonzero value when we are either in an
interrupt or have bh disabled via local_bh_disable().  Since we are
interested in only ignoring coverage from actual interrupts, do a proper
check instead of just calling in_interrupt().

As a result of this change, kcov will start to collect coverage from
within local_bh_disable()/local_bh_enable() sections.

Link: http://lkml.kernel.org/r/1476115803-20712-1-git-send-email-andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Nicolai Stange <nicstange@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: James Morse <james.morse@arm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 8d44b3f..30e6d05 100644 (file)
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -53,8 +53,15 @@ void notrace __sanitizer_cov_trace_pc(void)
        /*
         * We are interested in code coverage as a function of a syscall inputs,
         * so we ignore code executed in interrupts.
+        * The checks for whether we are in an interrupt are open-coded, because
+        * 1. We can't use in_interrupt() here, since it also returns true
+        *    when we are inside local_bh_disable() section.
+        * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
+        *    since that leads to slower generated code (three separate tests,
+        *    one for each of the flags).
         */
-       if (!t || in_interrupt())
+       if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
+                                                       | NMI_MASK)))
                return;
        mode = READ_ONCE(t->kcov_mode);
        if (mode == KCOV_MODE_TRACE) {