diff options
| -rw-r--r-- | arch/x86/Kconfig | 1 | ||||
| -rw-r--r-- | arch/x86/include/asm/vdso/gettimeofday.h | 31 |
2 files changed, 23 insertions, 9 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 4fff6ed46e90..4e251ba3bad2 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -168,6 +168,7 @@ config X86 select GENERIC_TIME_VSYSCALL select GENERIC_GETTIMEOFDAY select GENERIC_VDSO_TIME_NS + select GENERIC_VDSO_OVERFLOW_PROTECT select GUP_GET_PXX_LOW_HIGH if X86_PAE select HARDIRQS_SW_RESEND select HARDLOCKUP_CHECK_TIMESTAMP if X86_64 diff --git a/arch/x86/include/asm/vdso/gettimeofday.h b/arch/x86/include/asm/vdso/gettimeofday.h index 5727dedd3549..0ef36190abe6 100644 --- a/arch/x86/include/asm/vdso/gettimeofday.h +++ b/arch/x86/include/asm/vdso/gettimeofday.h @@ -319,18 +319,31 @@ static inline bool arch_vdso_cycles_ok(u64 cycles) */ static __always_inline u64 vdso_calc_ns(const struct vdso_data *vd, u64 cycles, u64 base) { - /* - * Due to the MSB/Sign-bit being used as invalid marker (see - * arch_vdso_cycles_valid() above), the effective mask is S64_MAX. - */ - u64 delta = (cycles - vd->cycle_last) & S64_MAX; + u64 delta = cycles - vd->cycle_last; /* - * Due to the above mentioned TSC wobbles, filter out negative motion. - * Per the above masking, the effective sign bit is now bit 62. + * Negative motion and deltas which can cause multiplication + * overflow require special treatment. This check covers both as + * negative motion is guaranteed to be greater than @vd::max_cycles + * due to unsigned comparison. + * + * Due to the MSB/Sign-bit being used as invalid marker (see + * arch_vdso_cycles_valid() above), the effective mask is S64_MAX, + * but that case is also unlikely and will also take the unlikely path + * here. */ - if (unlikely(delta & (1ULL << 62))) - return base >> vd->shift; + if (unlikely(delta > vd->max_cycles)) { + /* + * Due to the above mentioned TSC wobbles, filter out + * negative motion. Per the above masking, the effective + * sign bit is now bit 62. + */ + if (delta & (1ULL << 62)) + return base >> vd->shift; + + /* Handle multiplication overflow gracefully */ + return mul_u64_u32_add_u64_shr(delta & S64_MAX, vd->mult, base, vd->shift); + } return ((delta * vd->mult) + base) >> vd->shift; } |