Subject: [PATCH V2 06/19] vdso: Add vdso_data::max_cycles

From: Adrian Hunter <[email-masked]>
Date: Mon, 25 Mar 2024 08:40:10 +0200

Add vdso_data::max_cycles in preparation to use it to detect potential
multiplication overflow.

Suggested-by: Thomas Gleixner <[email-masked]>
Signed-off-by: Adrian Hunter <[email-masked]>
---
 include/vdso/datapage.h | 4 ++++
 kernel/time/vsyscall.c  | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index 5d5c0b8efff2..6c3d67d6b758 100644
--- a/include/vdso/datapage.h
+++ b/include/vdso/datapage.h
@@ -67,6 +67,7 @@ struct vdso_timestamp {
  * @seq:		timebase sequence counter
  * @clock_mode:		clock mode
  * @cycle_last:		timebase at clocksource init
+ * @max_cycles:		maximum cycles which won't overflow 64bit multiplication
  * @mask:		clocksource mask
  * @mult:		clocksource multiplier
  * @shift:		clocksource shift
@@ -98,6 +99,9 @@ struct vdso_data {
 
 	s32			clock_mode;
 	u64			cycle_last;
+#ifdef CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT
+	u64			max_cycles;
+#endif
 	u64			mask;
 	u32			mult;
 	u32			shift;
diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index f0d5062d9cbc..9193d6133e5d 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -22,10 +22,16 @@ static inline void update_vdso_data(struct vdso_data *vdata,
 	u64 nsec, sec;
 
 	vdata[CS_HRES_COARSE].cycle_last	= tk->tkr_mono.cycle_last;
+#ifdef CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT
+	vdata[CS_HRES_COARSE].max_cycles	= tk->tkr_mono.clock->max_cycles;
+#endif
 	vdata[CS_HRES_COARSE].mask		= tk->tkr_mono.mask;
 	vdata[CS_HRES_COARSE].mult		= tk->tkr_mono.mult;
 	vdata[CS_HRES_COARSE].shift		= tk->tkr_mono.shift;
 	vdata[CS_RAW].cycle_last		= tk->tkr_raw.cycle_last;
+#ifdef CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT
+	vdata[CS_RAW].max_cycles		= tk->tkr_raw.clock->max_cycles;
+#endif
 	vdata[CS_RAW].mask			= tk->tkr_raw.mask;
 	vdata[CS_RAW].mult			= tk->tkr_raw.mult;
 	vdata[CS_RAW].shift			= tk->tkr_raw.shift;
-- 
2.34.1