linux-kernel - [PATCH] lib/vdso: use CLOCK_REALTIME

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Message-Id: <20200611155804.65204-1-salyzyn@android.com>
Date:   Thu, 11 Jun 2020 08:57:50 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com, Chiawei Wang <chiaweiwang@...gle.com>,
        Mark Salyzyn <salyzyn@...roid.com>, stable@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincenzo Frascino <vincenzo.frascino@....com>
Subject: [PATCH] lib/vdso: use CLOCK_REALTIME_COARSE for time()

From: Chiawei Wang <chiaweiwang@...gle.com>

CLOCK_REALTIME in vdso data won't be updated if
__arch_use_vsyscall() returns false. It will let time()
return an incorrect time value. Since time() is designed
to return the seconds since the Epoch, using
CLOCK_REALTIME_COARSE can still fulfill the request and
never fails.

Signed-off-by: Chiawei Wang <chiaweiwang@...gle.com>
Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
Cc: linux-kernel@...r.kernel.org
Cc: kernel-team@...roid.com
Cc: stable@...r.kernel.org # 5.4+
---
 lib/vdso/gettimeofday.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index a2909af4b924..7ea22096cbe2 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -324,7 +324,7 @@ __cvdso_time_data(const struct vdso_data *vd, __kernel_old_time_t *time)
 	    vd->clock_mode == VDSO_CLOCKMODE_TIMENS)
 		vd = __arch_get_timens_vdso_data();
 
-	t = READ_ONCE(vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME].sec);
+	t = READ_ONCE(vd[CS_HRES_COARSE].basetime[CLOCK_REALTIME_COARSE].sec);
 
 	if (time)
 		*time = t;
-- 
2.27.0.278.ge193c7cf3a9-goog