diff options
| author | Adrian Hunter <adrian.hunter@intel.com> | 2024-03-25 07:40:11 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2024-04-08 15:03:07 +0200 |
| commit | 456e3788bc7164c1c8298045e04068b8e3d8e413 (patch) | |
| tree | 09efbe2666a269c3da3a88e9dba4ff3498b30a23 /lib | |
| parent | vdso: Add vdso_data:: Max_cycles (diff) | |
| download | linux-456e3788bc7164c1c8298045e04068b8e3d8e413.tar.xz linux-456e3788bc7164c1c8298045e04068b8e3d8e413.zip | |
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
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/vdso/gettimeofday.c | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 9fa90e0794c9..9c3a8d2440c9 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 */ |