@@ -13,6 +13,18 @@
# define VDSO_DELTA_MASK(vd) (vd->mask)
#endif
+#ifdef CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT
+static __always_inline bool vdso_delta_ok(const struct vdso_data *vd, u64 delta)
+{
+ return delta < vd->max_cycles;
+}
+#else
+static __always_inline bool vdso_delta_ok(const struct vdso_data *vd, u64 delta)
+{
+ return true;
+}
+#endif
+
#ifndef vdso_shift_ns
static __always_inline u64 vdso_shift_ns(u64 ns, u32 shift)
{
@@ -28,7 +40,10 @@ static __always_inline u64 vdso_calc_ns(const struct vdso_data *vd, u64 cycles,
{
u64 delta = (cycles - vd->cycle_last) & VDSO_DELTA_MASK(vd);
- return vdso_shift_ns((delta * vd->mult) + base, vd->shift);
+ if (likely(vdso_delta_ok(vd, delta)))
+ return vdso_shift_ns((delta * vd->mult) + base, vd->shift);
+
+ return mul_u64_u32_add_u64_shr(delta, vd->mult, base, vd->shift);
}
#endif /* vdso_calc_ns */
Kernel timekeeping is designed to keep the change in cycles (since the last timer interrupt) below max_cycles, which prevents multiplication overflow when converting cycles to nanoseconds. However, if timer interrupts stop, the calculation will eventually overflow. Add protection against that, enabled by config option CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT. Check against max_cycles, falling back to a slower higher precision calculation. Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> --- lib/vdso/gettimeofday.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)