[Devel] [PATCH rh7 4/4] ms/kcov: properly check if we are in an interrupt

[Andrey Ryabinin]

From: Andrey Konovalov <andreyknvl at google.com>

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().

Link: http://lkml.kernel.org/r/1476115803-20712-1-git-send-email-andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
Acked-by: Dmitry Vyukov <dvyukov at google.com>
Cc: Nicolai Stange <nicstange at gmail.com>
Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: James Morse <james.morse at arm.com>
Cc: Vegard Nossum <vegard.nossum at oracle.com>
Cc: Quentin Casasnovas <quentin.casasnovas at oracle.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 kernel/kcov.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 91b00e6..83b50fe 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -6,6 +6,7 @@
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
+#include <linux/preempt_mask.h>
 #include <linux/printk.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
@@ -54,8 +55,15 @@ 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) {
-- 
2.7.3