lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 6 Mar 2015 18:49:57 -0800 From: John Stultz <john.stultz@...aro.org> To: lkml <linux-kernel@...r.kernel.org> Cc: John Stultz <john.stultz@...aro.org>, Dave Jones <davej@...emonkey.org.uk>, Linus Torvalds <torvalds@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Richard Cochran <richardcochran@...il.com>, Prarit Bhargava <prarit@...hat.com>, Stephen Boyd <sboyd@...eaurora.org>, Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <peterz@...radead.org> Subject: [PATCH 06/12] time: Add infrastructure to cap clocksource reads to the max_cycles value When calculating the current delta since the last tick, we currently have no hard protections to prevent a multiplciation overflow from ocurring. This patch introduces infrastructure to allow a capp that limits the read delta value to the max_cycles value, which is where an overflow would occur. Since this is in the hotpath, it adds the extra checking under CONFIG_DEBUG_TIMEKEEPING. There was some concern that capping time like this could cause problems as we may stop expiring timers, which could go circular if the timer that triggers time accumulation were misscheduled too far in the future, which would cause time to stop. However, since the mult overflow would result in a smaller time value, we would effectively have the same problem there. Cc: Dave Jones <davej@...emonkey.org.uk> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Richard Cochran <richardcochran@...il.com> Cc: Prarit Bhargava <prarit@...hat.com> Cc: Stephen Boyd <sboyd@...eaurora.org> Cc: Ingo Molnar <mingo@...nel.org> Cc: Peter Zijlstra <peterz@...radead.org> Signed-off-by: John Stultz <john.stultz@...aro.org> --- kernel/time/timekeeping.c | 39 +++++++++++++++++++++++++++------------ 1 file changed, 27 insertions(+), 12 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 7e9d433..8b9e328 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -134,11 +134,34 @@ static void timekeeping_check_update(struct timekeeper *tk, cycle_t offset) " the %s 50%% safety margin (%lld)\n", offset, name, max_cycles>>1); } + +static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr) +{ + cycle_t cycle_now, delta; + + /* read clocksource */ + cycle_now = tkr->read(tkr->clock); + + /* calculate the delta since the last update_wall_time */ + delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask); + + /* Cap delta value to the max_cycles values to avoid mult overflows */ + if (unlikely(delta > tkr->clock->max_cycles)) + delta = tkr->clock->max_cycles; + + return delta; +} #else static inline void timekeeping_check_update(struct timekeeper *tk, cycle_t offset) { } +static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr) +{ + /* calculate the delta since the last update_wall_time */ + return clocksource_delta(tkr->read(tkr->clock), tkr->cycle_last, + tkr->mask); +} #endif /** @@ -216,14 +239,10 @@ static inline u32 arch_gettimeoffset(void) { return 0; } static inline s64 timekeeping_get_ns(struct tk_read_base *tkr) { - cycle_t cycle_now, delta; + cycle_t delta; s64 nsec; - /* read clocksource: */ - cycle_now = tkr->read(tkr->clock); - - /* calculate the delta since the last update_wall_time: */ - delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask); + delta = timekeeping_get_delta(tkr); nsec = delta * tkr->mult + tkr->xtime_nsec; nsec >>= tkr->shift; @@ -235,14 +254,10 @@ static inline s64 timekeeping_get_ns(struct tk_read_base *tkr) static inline s64 timekeeping_get_ns_raw(struct timekeeper *tk) { struct clocksource *clock = tk->tkr.clock; - cycle_t cycle_now, delta; + cycle_t delta; s64 nsec; - /* read clocksource: */ - cycle_now = tk->tkr.read(clock); - - /* calculate the delta since the last update_wall_time: */ - delta = clocksource_delta(cycle_now, tk->tkr.cycle_last, tk->tkr.mask); + delta = timekeeping_get_delta(&tk->tkr); /* convert delta to nanoseconds. */ nsec = clocksource_cyc2ns(delta, clock->mult, clock->shift); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists