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 01/16] futex: convert futex_pi_state.refcount to refcount_t Date: Wed, 15 Nov 2017 16:03:25 +0200 [thread overview] Message-ID: <1510754620-27088-2-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 futex_pi_state.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 futex_pi_state.refcount it might make a difference in following places: - get_pi_state() and exit_pi_state_list(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_pi_state(): 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> --- kernel/futex.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 76ed592..907055f 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -67,6 +67,7 @@ #include <linux/freezer.h> #include <linux/bootmem.h> #include <linux/fault-inject.h> +#include <linux/refcount.h> #include <asm/futex.h> @@ -209,7 +210,7 @@ struct futex_pi_state { struct rt_mutex pi_mutex; struct task_struct *owner; - atomic_t refcount; + refcount_t refcount; union futex_key key; } __randomize_layout; @@ -795,7 +796,7 @@ static int refill_pi_state_cache(void) INIT_LIST_HEAD(&pi_state->list); /* pi_mutex gets initialized later */ pi_state->owner = NULL; - atomic_set(&pi_state->refcount, 1); + refcount_set(&pi_state->refcount, 1); pi_state->key = FUTEX_KEY_INIT; current->pi_state_cache = pi_state; @@ -815,7 +816,7 @@ static struct futex_pi_state *alloc_pi_state(void) static void get_pi_state(struct futex_pi_state *pi_state) { - WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount)); + WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount)); } /* @@ -827,7 +828,7 @@ static void put_pi_state(struct futex_pi_state *pi_state) if (!pi_state) return; - if (!atomic_dec_and_test(&pi_state->refcount)) + if (!refcount_dec_and_test(&pi_state->refcount)) return; /* @@ -857,7 +858,7 @@ static void put_pi_state(struct futex_pi_state *pi_state) * refcount is at 0 - put it back to 1. */ pi_state->owner = NULL; - atomic_set(&pi_state->refcount, 1); + refcount_set(&pi_state->refcount, 1); current->pi_state_cache = pi_state; } } @@ -918,7 +919,7 @@ void exit_pi_state_list(struct task_struct *curr) * In that case; drop the locks to let put_pi_state() make * progress and retry the loop. */ - if (!atomic_inc_not_zero(&pi_state->refcount)) { + if (!refcount_inc_not_zero(&pi_state->refcount)) { raw_spin_unlock_irq(&curr->pi_lock); cpu_relax(); raw_spin_lock_irq(&curr->pi_lock); @@ -1074,7 +1075,7 @@ static int attach_to_pi_state(u32 __user *uaddr, u32 uval, * and futex_wait_requeue_pi() as it cannot go to 0 and consequently * free pi_state before we can take a reference ourselves. */ - WARN_ON(!atomic_read(&pi_state->refcount)); + WARN_ON(!refcount_read(&pi_state->refcount)); /* * Now that we have a pi_state, we can acquire wait_lock -- 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 01/16] futex: convert futex_pi_state.refcount to refcount_t Date: Wed, 15 Nov 2017 16:03:25 +0200 [thread overview] Message-ID: <1510754620-27088-2-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 futex_pi_state.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 futex_pi_state.refcount it might make a difference in following places: - get_pi_state() and exit_pi_state_list(): increment in refcount_inc_not_zero() only guarantees control dependency on success vs. fully ordered atomic counterpart - put_pi_state(): 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> --- kernel/futex.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index 76ed592..907055f 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -67,6 +67,7 @@ #include <linux/freezer.h> #include <linux/bootmem.h> #include <linux/fault-inject.h> +#include <linux/refcount.h> #include <asm/futex.h> @@ -209,7 +210,7 @@ struct futex_pi_state { struct rt_mutex pi_mutex; struct task_struct *owner; - atomic_t refcount; + refcount_t refcount; union futex_key key; } __randomize_layout; @@ -795,7 +796,7 @@ static int refill_pi_state_cache(void) INIT_LIST_HEAD(&pi_state->list); /* pi_mutex gets initialized later */ pi_state->owner = NULL; - atomic_set(&pi_state->refcount, 1); + refcount_set(&pi_state->refcount, 1); pi_state->key = FUTEX_KEY_INIT; current->pi_state_cache = pi_state; @@ -815,7 +816,7 @@ static struct futex_pi_state *alloc_pi_state(void) static void get_pi_state(struct futex_pi_state *pi_state) { - WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount)); + WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount)); } /* @@ -827,7 +828,7 @@ static void put_pi_state(struct futex_pi_state *pi_state) if (!pi_state) return; - if (!atomic_dec_and_test(&pi_state->refcount)) + if (!refcount_dec_and_test(&pi_state->refcount)) return; /* @@ -857,7 +858,7 @@ static void put_pi_state(struct futex_pi_state *pi_state) * refcount is at 0 - put it back to 1. */ pi_state->owner = NULL; - atomic_set(&pi_state->refcount, 1); + refcount_set(&pi_state->refcount, 1); current->pi_state_cache = pi_state; } } @@ -918,7 +919,7 @@ void exit_pi_state_list(struct task_struct *curr) * In that case; drop the locks to let put_pi_state() make * progress and retry the loop. */ - if (!atomic_inc_not_zero(&pi_state->refcount)) { + if (!refcount_inc_not_zero(&pi_state->refcount)) { raw_spin_unlock_irq(&curr->pi_lock); cpu_relax(); raw_spin_lock_irq(&curr->pi_lock); @@ -1074,7 +1075,7 @@ static int attach_to_pi_state(u32 __user *uaddr, u32 uval, * and futex_wait_requeue_pi() as it cannot go to 0 and consequently * free pi_state before we can take a reference ourselves. */ - WARN_ON(!atomic_read(&pi_state->refcount)); + WARN_ON(!refcount_read(&pi_state->refcount)); /* * Now that we have a pi_state, we can acquire wait_lock -- 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 14:08 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 ` Elena Reshetova [this message] 2017-11-15 14:03 ` [PATCH 01/16] futex: convert futex_pi_state.refcount to refcount_t 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 ` [PATCH 08/16] perf: convert perf_event_context.refcount " Elena Reshetova 2017-11-15 14:03 ` 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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