From: Elena Reshetova <elena.reshetova@intel.com> To: mingo@redhat.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, tj@kernel.org, hannes@cmpxchg.org, lizefan@huawei.com, acme@kernel.org, alexander.shishkin@linux.intel.com, eparis@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, luto@kernel.org, keescook@chromium.org, tglx@linutronix.de, dvhart@infradead.org, ebiederm@xmission.com, linux-mm@kvack.org, axboe@kernel.dk, Elena Reshetova <elena.reshetova@intel.com> Subject: [PATCH 08/16] perf: convert perf_event_context.refcount to refcount_t Date: Wed, 15 Nov 2017 16:03:32 +0200 [thread overview] Message-ID: <1510754620-27088-9-git-send-email-elena.reshetova@intel.com> (raw) In-Reply-To: <1510754620-27088-1-git-send-email-elena.reshetova@intel.com> atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable perf_event_context.refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. **Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the perf_event_context.refcount it might make a difference in following places: - get_ctx(), perf_event_ctx_lock_nested(), perf_lock_task_context() and __perf_event_ctx_lock_double(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_ctx(): decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook <keescook@chromium.org> Reviewed-by: David Windsor <dwindsor@gmail.com> Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> --- include/linux/perf_event.h | 3 ++- kernel/events/core.c | 12 ++++++------ 2 files changed, 8 insertions(+), 7 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 2c9c87d..6a78705 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -54,6 +54,7 @@ struct perf_guest_info_callbacks { #include <linux/perf_regs.h> #include <linux/workqueue.h> #include <linux/cgroup.h> +#include <linux/refcount.h> #include <asm/local.h> struct perf_callchain_entry { @@ -718,7 +719,7 @@ struct perf_event_context { int nr_stat; int nr_freq; int rotate_disable; - atomic_t refcount; + refcount_t refcount; struct task_struct *task; /* diff --git a/kernel/events/core.c b/kernel/events/core.c index d084a97..29c381f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1148,7 +1148,7 @@ static void perf_event_ctx_deactivate(struct perf_event_context *ctx) static void get_ctx(struct perf_event_context *ctx) { - WARN_ON(!atomic_inc_not_zero(&ctx->refcount)); + WARN_ON(!refcount_inc_not_zero(&ctx->refcount)); } static void free_ctx(struct rcu_head *head) @@ -1162,7 +1162,7 @@ static void free_ctx(struct rcu_head *head) static void put_ctx(struct perf_event_context *ctx) { - if (atomic_dec_and_test(&ctx->refcount)) { + if (refcount_dec_and_test(&ctx->refcount)) { if (ctx->parent_ctx) put_ctx(ctx->parent_ctx); if (ctx->task && ctx->task != TASK_TOMBSTONE) @@ -1240,7 +1240,7 @@ perf_event_ctx_lock_nested(struct perf_event *event, int nesting) again: rcu_read_lock(); ctx = READ_ONCE(event->ctx); - if (!atomic_inc_not_zero(&ctx->refcount)) { + if (!refcount_inc_not_zero(&ctx->refcount)) { rcu_read_unlock(); goto again; } @@ -1373,7 +1373,7 @@ perf_lock_task_context(struct task_struct *task, int ctxn, unsigned long *flags) } if (ctx->task == TASK_TOMBSTONE || - !atomic_inc_not_zero(&ctx->refcount)) { + !refcount_inc_not_zero(&ctx->refcount)) { raw_spin_unlock(&ctx->lock); ctx = NULL; } else { @@ -3715,7 +3715,7 @@ static void __perf_event_init_context(struct perf_event_context *ctx) INIT_LIST_HEAD(&ctx->pinned_groups); INIT_LIST_HEAD(&ctx->flexible_groups); INIT_LIST_HEAD(&ctx->event_list); - atomic_set(&ctx->refcount, 1); + refcount_set(&ctx->refcount, 1); } static struct perf_event_context * @@ -9793,7 +9793,7 @@ __perf_event_ctx_lock_double(struct perf_event *group_leader, again: rcu_read_lock(); gctx = READ_ONCE(group_leader->ctx); - if (!atomic_inc_not_zero(&gctx->refcount)) { + if (!refcount_inc_not_zero(&gctx->refcount)) { rcu_read_unlock(); goto again; } -- 2.7.4
WARNING: multiple messages have this Message-ID (diff)
From: Elena Reshetova <elena.reshetova@intel.com> To: mingo@redhat.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, tj@kernel.org, hannes@cmpxchg.org, lizefan@huawei.com, acme@kernel.org, alexander.shishkin@linux.intel.com, eparis@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, luto@kernel.org, keescook@chromium.org, tglx@linutronix.de, dvhart@infradead.org, ebiederm@xmission.com, linux-mm@kvack.org, axboe@kernel.dk, Elena Reshetova <elena.reshetova@intel.com> Subject: [PATCH 08/16] perf: convert perf_event_context.refcount to refcount_t Date: Wed, 15 Nov 2017 16:03:32 +0200 [thread overview] Message-ID: <1510754620-27088-9-git-send-email-elena.reshetova@intel.com> (raw) In-Reply-To: <1510754620-27088-1-git-send-email-elena.reshetova@intel.com> atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable perf_event_context.refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. **Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the perf_event_context.refcount it might make a difference in following places: - get_ctx(), perf_event_ctx_lock_nested(), perf_lock_task_context() and __perf_event_ctx_lock_double(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_ctx(): decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook <keescook@chromium.org> Reviewed-by: David Windsor <dwindsor@gmail.com> Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> --- include/linux/perf_event.h | 3 ++- kernel/events/core.c | 12 ++++++------ 2 files changed, 8 insertions(+), 7 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 2c9c87d..6a78705 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -54,6 +54,7 @@ struct perf_guest_info_callbacks { #include <linux/perf_regs.h> #include <linux/workqueue.h> #include <linux/cgroup.h> +#include <linux/refcount.h> #include <asm/local.h> struct perf_callchain_entry { @@ -718,7 +719,7 @@ struct perf_event_context { int nr_stat; int nr_freq; int rotate_disable; - atomic_t refcount; + refcount_t refcount; struct task_struct *task; /* diff --git a/kernel/events/core.c b/kernel/events/core.c index d084a97..29c381f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -1148,7 +1148,7 @@ static void perf_event_ctx_deactivate(struct perf_event_context *ctx) static void get_ctx(struct perf_event_context *ctx) { - WARN_ON(!atomic_inc_not_zero(&ctx->refcount)); + WARN_ON(!refcount_inc_not_zero(&ctx->refcount)); } static void free_ctx(struct rcu_head *head) @@ -1162,7 +1162,7 @@ static void free_ctx(struct rcu_head *head) static void put_ctx(struct perf_event_context *ctx) { - if (atomic_dec_and_test(&ctx->refcount)) { + if (refcount_dec_and_test(&ctx->refcount)) { if (ctx->parent_ctx) put_ctx(ctx->parent_ctx); if (ctx->task && ctx->task != TASK_TOMBSTONE) @@ -1240,7 +1240,7 @@ perf_event_ctx_lock_nested(struct perf_event *event, int nesting) again: rcu_read_lock(); ctx = READ_ONCE(event->ctx); - if (!atomic_inc_not_zero(&ctx->refcount)) { + if (!refcount_inc_not_zero(&ctx->refcount)) { rcu_read_unlock(); goto again; } @@ -1373,7 +1373,7 @@ perf_lock_task_context(struct task_struct *task, int ctxn, unsigned long *flags) } if (ctx->task == TASK_TOMBSTONE || - !atomic_inc_not_zero(&ctx->refcount)) { + !refcount_inc_not_zero(&ctx->refcount)) { raw_spin_unlock(&ctx->lock); ctx = NULL; } else { @@ -3715,7 +3715,7 @@ static void __perf_event_init_context(struct perf_event_context *ctx) INIT_LIST_HEAD(&ctx->pinned_groups); INIT_LIST_HEAD(&ctx->flexible_groups); INIT_LIST_HEAD(&ctx->event_list); - atomic_set(&ctx->refcount, 1); + refcount_set(&ctx->refcount, 1); } static struct perf_event_context * @@ -9793,7 +9793,7 @@ __perf_event_ctx_lock_double(struct perf_event *group_leader, again: rcu_read_lock(); gctx = READ_ONCE(group_leader->ctx); - if (!atomic_inc_not_zero(&gctx->refcount)) { + if (!refcount_inc_not_zero(&gctx->refcount)) { rcu_read_unlock(); goto again; } -- 2.7.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-11-15 14:10 UTC|newest] Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-15 14:03 [PATCH 00/16] v6 kernel core pieces refcount conversions Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 01/16] futex: convert futex_pi_state.refcount to refcount_t Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 02/16] sched: convert sighand_struct.count " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 03/16] sched: convert signal_struct.sigcnt " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 04/16] sched: convert user_struct.__count " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-17 0:16 ` Kees Cook 2017-11-17 0:16 ` Kees Cook 2017-11-15 14:03 ` [PATCH 05/16] sched: convert numa_group.refcount " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 06/16] sched/task_struct: convert task_struct.usage " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 07/16] sched/task_struct: convert task_struct.stack_refcount " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova [this message] 2017-11-15 14:03 ` [PATCH 08/16] perf: convert perf_event_context.refcount " Elena Reshetova 2017-11-15 14:03 ` [PATCH 09/16] perf/ring_buffer: convert ring_buffer.refcount " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 10/16] perf/ring_buffer: convert ring_buffer.aux_refcount " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 11/16] uprobes: convert uprobe.ref " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 14:03 ` [PATCH 12/16] nsproxy: convert nsproxy.count " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-15 16:36 ` Eric W. Biederman 2017-11-15 16:36 ` Eric W. Biederman 2017-11-15 16:36 ` Eric W. Biederman 2017-11-17 7:16 ` Reshetova, Elena 2017-11-17 7:16 ` Reshetova, Elena 2017-11-15 14:03 ` [PATCH 13/16] groups: convert group_info.usage " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-17 0:08 ` Kees Cook 2017-11-17 0:08 ` Kees Cook 2017-11-15 14:03 ` [PATCH 14/16] creds: convert cred.usage " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-17 0:14 ` Kees Cook 2017-11-17 0:14 ` Kees Cook 2017-11-15 14:03 ` [PATCH 15/16] kcov: convert kcov.refcount " Elena Reshetova 2017-11-15 14:03 ` Elena Reshetova 2017-11-17 0:10 ` Kees Cook 2017-11-17 0:10 ` Kees Cook 2017-11-15 14:03 ` [PATCH 16/16] bdi: convert bdi_writeback_congested.refcnt from atomic_t " Elena Reshetova 2018-12-05 1:06 ` [PATCH 00/16] v6 kernel core pieces refcount conversions Kees Cook
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