| 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
| ||
|
Message-ID: <CANpmjNNsDG7J=ZsuA40opV1b3xKMF0P8P3yCsufowJCRegGa7w@mail.gmail.com>
Date: Thu, 31 Oct 2024 08:00:00 +0100
From: Marco Elver <elver@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>, "Paul E. McKenney" <paulmck@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Mark Rutland <mark.rutland@....com>,
Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
linux-kernel@...r.kernel.org, Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH] kcsan, seqlock: Support seqcount_latch_t
On Wed, 30 Oct 2024 at 21:48, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Tue, Oct 29, 2024 at 09:49:21PM +0100, Marco Elver wrote:
>
> > Something like this?
> >
> > ------ >8 ------
> >
> > Author: Marco Elver <elver@...gle.com>
> > Date: Tue Oct 29 21:16:21 2024 +0100
> >
> > time/sched_clock: Swap update_clock_read_data() latch writes
> >
> > Swap the writes to the odd and even copies to make the writer critical
> > section look like all other seqcount_latch writers.
> >
> > With that, we can also add the raw_write_seqcount_latch_end() to clearly
> > denote the end of the writer section.
> >
> > Signed-off-by: Marco Elver <elver@...gle.com>
> >
> > diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> > index 68d6c1190ac7..311c90a0e86e 100644
> > --- a/kernel/time/sched_clock.c
> > +++ b/kernel/time/sched_clock.c
> > @@ -119,9 +119,6 @@ unsigned long long notrace sched_clock(void)
> > */
> > static void update_clock_read_data(struct clock_read_data *rd)
> > {
> > - /* update the backup (odd) copy with the new data */
> > - cd.read_data[1] = *rd;
> > -
> > /* steer readers towards the odd copy */
> > raw_write_seqcount_latch(&cd.seq);
> >
> > @@ -130,6 +127,11 @@ static void update_clock_read_data(struct clock_read_data *rd)
> >
> > /* switch readers back to the even copy */
> > raw_write_seqcount_latch(&cd.seq);
> > +
> > + /* update the backup (odd) copy with the new data */
> > + cd.read_data[1] = *rd;
> > +
> > + raw_write_seqcount_latch_end(&cd.seq);
> > }
> >
> > /*
>
> That looks about right :-)
>
> > ------ >8 ------
> >
> > I also noticed your d16317de9b41 ("seqlock/latch: Provide
> > raw_read_seqcount_latch_retry()") to get rid of explicit instrumentation
> > in noinstr.
> >
> > Not sure how to resolve that. We have that objtool support to erase
> > calls in noinstr code (is_profiling_func), but that's x86 only.
> >
> > I could also make kcsan_atomic_next(0) noinstr compatible by checking if
> > the ret IP is in noinstr, and immediately return if it is.
> >
> > Preferences?
>
> Something like this perhaps?
Looks good.
Let me try to assemble the pieces into a patch. (Your SOB will be
needed - either now or later.)
Thanks,
-- Marco
> ---
> arch/x86/kernel/tsc.c | 5 +++--
> include/linux/rbtree_latch.h | 14 ++++++++------
> include/linux/seqlock.h | 31 ++++++++++++++++++++++++++++++-
> kernel/printk/printk.c | 9 +++++----
> kernel/time/sched_clock.c | 20 ++++++++++++--------
> kernel/time/timekeeping.c | 10 ++++++----
> 6 files changed, 64 insertions(+), 25 deletions(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index dfe6847fd99e..67aeaba4ba9c 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -174,10 +174,11 @@ static void __set_cyc2ns_scale(unsigned long khz, int cpu, unsigned long long ts
>
> c2n = per_cpu_ptr(&cyc2ns, cpu);
>
> - raw_write_seqcount_latch(&c2n->seq);
> + write_seqcount_latch_begin(&c2n->seq);
> c2n->data[0] = data;
> - raw_write_seqcount_latch(&c2n->seq);
> + write_seqcount_latch(&c2n->seq);
> c2n->data[1] = data;
> + write_seqcount_latch_end(&c2n->seq);
> }
>
> static void set_cyc2ns_scale(unsigned long khz, int cpu, unsigned long long tsc_now)
> diff --git a/include/linux/rbtree_latch.h b/include/linux/rbtree_latch.h
> index 6a0999c26c7c..bc992c61b7ce 100644
> --- a/include/linux/rbtree_latch.h
> +++ b/include/linux/rbtree_latch.h
> @@ -145,10 +145,11 @@ latch_tree_insert(struct latch_tree_node *node,
> struct latch_tree_root *root,
> const struct latch_tree_ops *ops)
> {
> - raw_write_seqcount_latch(&root->seq);
> + write_seqcount_latch_begin(&root->seq);
> __lt_insert(node, root, 0, ops->less);
> - raw_write_seqcount_latch(&root->seq);
> + write_seqcount_latch(&root->seq);
> __lt_insert(node, root, 1, ops->less);
> + write_seqcount_latch_end(&root->seq);
> }
>
> /**
> @@ -172,10 +173,11 @@ latch_tree_erase(struct latch_tree_node *node,
> struct latch_tree_root *root,
> const struct latch_tree_ops *ops)
> {
> - raw_write_seqcount_latch(&root->seq);
> + write_seqcount_latch_begin(&root->seq);
> __lt_erase(node, root, 0);
> - raw_write_seqcount_latch(&root->seq);
> + write_seqcount_latch(&root->seq);
> __lt_erase(node, root, 1);
> + write_seqcount_latch_end(&root->seq);
> }
>
> /**
> @@ -204,9 +206,9 @@ latch_tree_find(void *key, struct latch_tree_root *root,
> unsigned int seq;
>
> do {
> - seq = raw_read_seqcount_latch(&root->seq);
> + seq = read_seqcount_latch(&root->seq);
> node = __lt_find(key, root, seq & 1, ops->comp);
> - } while (raw_read_seqcount_latch_retry(&root->seq, seq));
> + } while (read_seqcount_latch_retry(&root->seq, seq));
>
> return node;
> }
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index fffeb754880f..9c2751087185 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -621,6 +621,12 @@ static __always_inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *
> return READ_ONCE(s->seqcount.sequence);
> }
>
> +static __always_inline unsigned read_seqcount_latch(const seqcount_latch_t *s)
> +{
> + kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);
> + return raw_read_seqcount_latch(s);
> +}
> +
> /**
> * raw_read_seqcount_latch_retry() - end a seqcount_latch_t read section
> * @s: Pointer to seqcount_latch_t
> @@ -635,6 +641,13 @@ raw_read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
> return unlikely(READ_ONCE(s->seqcount.sequence) != start);
> }
>
> +static __always_inline int
> +read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
> +{
> + kcsan_atomic_next(0);
> + return raw_read_seqcount_latch_retry(s, start);
> +}
> +
> /**
> * raw_write_seqcount_latch() - redirect latch readers to even/odd copy
> * @s: Pointer to seqcount_latch_t
> @@ -716,13 +729,29 @@ raw_read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
> * When data is a dynamic data structure; one should use regular RCU
> * patterns to manage the lifetimes of the objects within.
> */
> -static inline void raw_write_seqcount_latch(seqcount_latch_t *s)
> +static __always_inline void raw_write_seqcount_latch(seqcount_latch_t *s)
> {
> smp_wmb(); /* prior stores before incrementing "sequence" */
> s->seqcount.sequence++;
> smp_wmb(); /* increment "sequence" before following stores */
> }
>
> +static __always_inline void write_seqcount_latch_begin(seqcount_latch_t *s)
> +{
> + kcsan_nestable_atomic_begin();
> + raw_write_seqcount_latch(s);
> +}
> +
> +static __always_inline void write_seqcount_latch(seqcount_latch_t *s)
> +{
> + raw_write_seqcount_latch(s);
> +}
> +
> +static __always_inline void write_seqcount_latch_end(seqcount_latch_t *s)
> +{
> + kcsan_nestable_atomic_end();
> +}
> +
> #define __SEQLOCK_UNLOCKED(lockname) \
> { \
> .seqcount = SEQCNT_SPINLOCK_ZERO(lockname, &(lockname).lock), \
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index beb808f4c367..19911c8fa7b6 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -560,10 +560,11 @@ bool printk_percpu_data_ready(void)
> /* Must be called under syslog_lock. */
> static void latched_seq_write(struct latched_seq *ls, u64 val)
> {
> - raw_write_seqcount_latch(&ls->latch);
> + write_seqcount_latch_begin(&ls->latch);
> ls->val[0] = val;
> - raw_write_seqcount_latch(&ls->latch);
> + write_seqcount_latch(&ls->latch);
> ls->val[1] = val;
> + write_seqcount_latch_end(&ls->latch);
> }
>
> /* Can be called from any context. */
> @@ -574,10 +575,10 @@ static u64 latched_seq_read_nolock(struct latched_seq *ls)
> u64 val;
>
> do {
> - seq = raw_read_seqcount_latch(&ls->latch);
> + seq = read_seqcount_latch(&ls->latch);
> idx = seq & 0x1;
> val = ls->val[idx];
> - } while (raw_read_seqcount_latch_retry(&ls->latch, seq));
> + } while (read_seqcount_latch_retry(&ls->latch, seq));
>
> return val;
> }
> diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> index 68d6c1190ac7..4958b40ba6c9 100644
> --- a/kernel/time/sched_clock.c
> +++ b/kernel/time/sched_clock.c
> @@ -71,13 +71,13 @@ static __always_inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
>
> notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
> {
> - *seq = raw_read_seqcount_latch(&cd.seq);
> + *seq = read_seqcount_latch(&cd.seq);
> return cd.read_data + (*seq & 1);
> }
>
> notrace int sched_clock_read_retry(unsigned int seq)
> {
> - return raw_read_seqcount_latch_retry(&cd.seq, seq);
> + return read_seqcount_latch_retry(&cd.seq, seq);
> }
>
> unsigned long long noinstr sched_clock_noinstr(void)
> @@ -102,7 +102,9 @@ unsigned long long notrace sched_clock(void)
> {
> unsigned long long ns;
> preempt_disable_notrace();
> + kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);
> ns = sched_clock_noinstr();
> + kcsan_atomic_next(0);
> preempt_enable_notrace();
> return ns;
> }
> @@ -119,17 +121,19 @@ unsigned long long notrace sched_clock(void)
> */
> static void update_clock_read_data(struct clock_read_data *rd)
> {
> - /* update the backup (odd) copy with the new data */
> - cd.read_data[1] = *rd;
> -
> /* steer readers towards the odd copy */
> - raw_write_seqcount_latch(&cd.seq);
> + write_seqcount_latch_begin(&cd.seq);
>
> /* now its safe for us to update the normal (even) copy */
> cd.read_data[0] = *rd;
>
> /* switch readers back to the even copy */
> - raw_write_seqcount_latch(&cd.seq);
> + write_seqcount_latch(&cd.seq);
> +
> + /* update the backup (odd) copy with the new data */
> + cd.read_data[1] = *rd;
> +
> + write_seqcount_latch_end(&cd.seq);
> }
>
> /*
> @@ -267,7 +271,7 @@ void __init generic_sched_clock_init(void)
> */
> static u64 notrace suspended_sched_clock_read(void)
> {
> - unsigned int seq = raw_read_seqcount_latch(&cd.seq);
> + unsigned int seq = read_seqcount_latch(&cd.seq);
>
> return cd.read_data[seq & 1].epoch_cyc;
> }
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 7e6f409bf311..2ca26bfeb8f3 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -424,16 +424,18 @@ static void update_fast_timekeeper(const struct tk_read_base *tkr,
> struct tk_read_base *base = tkf->base;
>
> /* Force readers off to base[1] */
> - raw_write_seqcount_latch(&tkf->seq);
> + write_seqcount_latch_begin(&tkf->seq);
>
> /* Update base[0] */
> memcpy(base, tkr, sizeof(*base));
>
> /* Force readers back to base[0] */
> - raw_write_seqcount_latch(&tkf->seq);
> + write_seqcount_latch(&tkf->seq);
>
> /* Update base[1] */
> memcpy(base + 1, base, sizeof(*base));
> +
> + write_seqcount_latch_end(&tkf->seq);
> }
>
> static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
> @@ -443,11 +445,11 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
> u64 now;
>
> do {
> - seq = raw_read_seqcount_latch(&tkf->seq);
> + seq = read_seqcount_latch(&tkf->seq);
> tkr = tkf->base + (seq & 0x01);
> now = ktime_to_ns(tkr->base);
> now += __timekeeping_get_ns(tkr);
> - } while (raw_read_seqcount_latch_retry(&tkf->seq, seq));
> + } while (read_seqcount_latch_retry(&tkf->seq, seq));
>
> return now;
> }
Powered by blists - more mailing lists