Messages in this thread Patch in this message | | | Date | Mon, 08 Apr 2024 13:10:40 -0000 | From | "tip-bot2 for Adrian Hunter" <> | Subject | [tip: timers/core] vdso: Make delta calculation overflow safe |
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The following commit has been merged into the timers/core branch of tip:
Commit-ID: 456e3788bc7164c1c8298045e04068b8e3d8e413 Gitweb: https://git.kernel.org/tip/456e3788bc7164c1c8298045e04068b8e3d8e413 Author: Adrian Hunter <adrian.hunter@intel.com> AuthorDate: Mon, 25 Mar 2024 08:40:11 +02:00 Committer: Thomas Gleixner <tglx@linutronix.de> CommitterDate: Mon, 08 Apr 2024 15:03:07 +02:00
vdso: Make delta calculation overflow safe
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> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20240325064023.2997-8-adrian.hunter@intel.com
--- lib/vdso/gettimeofday.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 9fa90e0..9c3a8d2 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -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 */
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