From: Mathieu Desnoyers mathieu.desnoyers@efficios.com
mainline inclusion from mainline-5.4-rc1 commit 227a4aadc75ba22fcb6c4e1c078817b8cbaae4ce category: bugfix bugzilla: 28332 CVE: NA
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The membarrier_state field is located within the mm_struct, which is not guaranteed to exist when used from runqueue-lock-free iteration on runqueues by the membarrier system call.
Copy the membarrier_state from the mm_struct into the scheduler runqueue when the scheduler switches between mm.
When registering membarrier for mm, after setting the registration bit in the mm membarrier state, issue a synchronize_rcu() to ensure the scheduler observes the change. In order to take care of the case where a runqueue keeps executing the target mm without swapping to other mm, iterate over each runqueue and issue an IPI to copy the membarrier_state from the mm_struct into each runqueue which have the same mm which state has just been modified.
Move the mm membarrier_state field closer to pgd in mm_struct to use a cache line already touched by the scheduler switch_mm.
The membarrier_execve() (now membarrier_exec_mmap) hook now needs to clear the runqueue's membarrier state in addition to clear the mm membarrier state, so move its implementation into the scheduler membarrier code so it can access the runqueue structure.
Add memory barrier in membarrier_exec_mmap() prior to clearing the membarrier state, ensuring memory accesses executed prior to exec are not reordered with the stores clearing the membarrier state.
As suggested by Linus, move all membarrier.c RCU read-side locks outside of the for each cpu loops.
[Cheng Jian: use task_rcu_dereference in sync_runqueues_membarrier_state]
Suggested-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Chris Metcalf cmetcalf@ezchip.com Cc: Christoph Lameter cl@linux.com Cc: Eric W. Biederman ebiederm@xmission.com Cc: Kirill Tkhai tkhai@yandex.ru Cc: Mike Galbraith efault@gmx.de Cc: Oleg Nesterov oleg@redhat.com Cc: Paul E. McKenney paulmck@linux.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Russell King - ARM Linux admin linux@armlinux.org.uk Cc: Thomas Gleixner tglx@linutronix.de Link: https://lkml.kernel.org/r/20190919173705.2181-5-mathieu.desnoyers@efficios.c... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Cheng Jian cj.chengjian@huawei.com Reviewed-By: Xie XiuQi xiexiuqi@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/exec.c | 2 +- include/linux/mm_types.h | 14 +++- include/linux/sched/mm.h | 8 +-- kernel/sched/core.c | 4 +- kernel/sched/membarrier.c | 175 ++++++++++++++++++++++++++++++++++------------ kernel/sched/sched.h | 34 +++++++++ 6 files changed, 183 insertions(+), 54 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c index 10f1e24..f0a7a59 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1029,6 +1029,7 @@ static int exec_mmap(struct mm_struct *mm) } task_lock(tsk); active_mm = tsk->active_mm; + membarrier_exec_mmap(mm); tsk->mm = mm; tsk->active_mm = mm; activate_mm(active_mm, mm); @@ -1823,7 +1824,6 @@ static int __do_execve_file(int fd, struct filename *filename, /* execve succeeded */ current->fs->in_exec = 0; current->in_execve = 0; - membarrier_execve(current); rseq_execve(current); acct_update_integrals(current); task_numa_free(current, false); diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 3c639a8..178e9de 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -369,6 +369,16 @@ struct mm_struct { unsigned long highest_vm_end; /* highest vma end address */ pgd_t * pgd;
+#ifdef CONFIG_MEMBARRIER + /** + * @membarrier_state: Flags controlling membarrier behavior. + * + * This field is close to @pgd to hopefully fit in the same + * cache-line, which needs to be touched by switch_mm(). + */ + atomic_t membarrier_state; +#endif + /** * @mm_users: The number of users including userspace. * @@ -438,9 +448,7 @@ struct mm_struct { unsigned long flags; /* Must use atomic bitops to access */
struct core_state *core_state; /* coredumping support */ -#ifdef CONFIG_MEMBARRIER - atomic_t membarrier_state; -#endif + #ifdef CONFIG_AIO spinlock_t ioctx_lock; struct kioctx_table __rcu *ioctx_table; diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index e9d4e38..8c3eb9d 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -338,10 +338,8 @@ static inline void membarrier_mm_sync_core_before_usermode(struct mm_struct *mm) sync_core_before_usermode(); }
-static inline void membarrier_execve(struct task_struct *t) -{ - atomic_set(&t->mm->membarrier_state, 0); -} +extern void membarrier_exec_mmap(struct mm_struct *mm); + #else #ifdef CONFIG_ARCH_HAS_MEMBARRIER_CALLBACKS static inline void membarrier_arch_switch_mm(struct mm_struct *prev, @@ -350,7 +348,7 @@ static inline void membarrier_arch_switch_mm(struct mm_struct *prev, { } #endif -static inline void membarrier_execve(struct task_struct *t) +static inline void membarrier_exec_mmap(struct mm_struct *mm) { } static inline void membarrier_mm_sync_core_before_usermode(struct mm_struct *mm) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e2ee09d..5057f19 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2836,15 +2836,15 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev) else prev->active_mm = NULL; } else { // to user + membarrier_switch_mm(rq, prev->active_mm, next->mm); /* * sys_membarrier() requires an smp_mb() between setting - * rq->curr and returning to userspace. + * rq->curr / membarrier_switch_mm() and returning to userspace. * * The below provides this either through switch_mm(), or in * case 'prev->active_mm == next->mm' through * finish_task_switch()'s mmdrop(). */ - switch_mm_irqs_off(prev->active_mm, next->mm, next);
if (!prev->mm) { // from kernel diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index bcd0ff7..dc25e83 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -39,6 +39,39 @@ static void ipi_mb(void *info) smp_mb(); /* IPIs should be serializing but paranoid. */ }
+static void ipi_sync_rq_state(void *info) +{ + struct mm_struct *mm = (struct mm_struct *) info; + + if (current->mm != mm) + return; + this_cpu_write(runqueues.membarrier_state, + atomic_read(&mm->membarrier_state)); + /* + * Issue a memory barrier after setting + * MEMBARRIER_STATE_GLOBAL_EXPEDITED in the current runqueue to + * guarantee that no memory access following registration is reordered + * before registration. + */ + smp_mb(); +} + +void membarrier_exec_mmap(struct mm_struct *mm) +{ + /* + * Issue a memory barrier before clearing membarrier_state to + * guarantee that no memory access prior to exec is reordered after + * clearing this state. + */ + smp_mb(); + atomic_set(&mm->membarrier_state, 0); + /* + * Keep the runqueue membarrier_state in sync with this mm + * membarrier_state. + */ + this_cpu_write(runqueues.membarrier_state, 0); +} + static int membarrier_global_expedited(void) { int cpu; @@ -65,6 +98,7 @@ static int membarrier_global_expedited(void) }
cpus_read_lock(); + rcu_read_lock(); for_each_online_cpu(cpu) { struct task_struct *p;
@@ -79,17 +113,25 @@ static int membarrier_global_expedited(void) if (cpu == raw_smp_processor_id()) continue;
- rcu_read_lock(); + if (!(READ_ONCE(cpu_rq(cpu)->membarrier_state) & + MEMBARRIER_STATE_GLOBAL_EXPEDITED)) + continue; + + /* + * Skip the CPU if it runs a kernel thread. The scheduler + * leaves the prior task mm in place as an optimization when + * scheduling a kthread. + */ p = task_rcu_dereference(&cpu_rq(cpu)->curr); - if (p && p->mm && (atomic_read(&p->mm->membarrier_state) & - MEMBARRIER_STATE_GLOBAL_EXPEDITED)) { - if (!fallback) - __cpumask_set_cpu(cpu, tmpmask); - else - smp_call_function_single(cpu, ipi_mb, NULL, 1); - } - rcu_read_unlock(); + if (p->flags & PF_KTHREAD) + continue; + + if (!fallback) + __cpumask_set_cpu(cpu, tmpmask); + else + smp_call_function_single(cpu, ipi_mb, NULL, 1); } + rcu_read_unlock(); if (!fallback) { preempt_disable(); smp_call_function_many(tmpmask, ipi_mb, NULL, 1); @@ -145,6 +187,7 @@ static int membarrier_private_expedited(int flags) }
cpus_read_lock(); + rcu_read_lock(); for_each_online_cpu(cpu) { struct task_struct *p;
@@ -166,8 +209,8 @@ static int membarrier_private_expedited(int flags) else smp_call_function_single(cpu, ipi_mb, NULL, 1); } - rcu_read_unlock(); } + rcu_read_unlock(); if (!fallback) { preempt_disable(); smp_call_function_many(tmpmask, ipi_mb, NULL, 1); @@ -186,32 +229,78 @@ static int membarrier_private_expedited(int flags) return 0; }
+static int sync_runqueues_membarrier_state(struct mm_struct *mm) +{ + int membarrier_state = atomic_read(&mm->membarrier_state); + cpumask_var_t tmpmask; + int cpu; + + if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) { + this_cpu_write(runqueues.membarrier_state, membarrier_state); + + /* + * For single mm user, we can simply issue a memory barrier + * after setting MEMBARRIER_STATE_GLOBAL_EXPEDITED in the + * mm and in the current runqueue to guarantee that no memory + * access following registration is reordered before + * registration. + */ + smp_mb(); + return 0; + } + + if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) + return -ENOMEM; + + /* + * For mm with multiple users, we need to ensure all future + * scheduler executions will observe @mm's new membarrier + * state. + */ + synchronize_rcu(); + + /* + * For each cpu runqueue, if the task's mm match @mm, ensure that all + * @mm's membarrier state set bits are also set in in the runqueue's + * membarrier state. This ensures that a runqueue scheduling + * between threads which are users of @mm has its membarrier state + * updated. + */ + cpus_read_lock(); + rcu_read_lock(); + for_each_online_cpu(cpu) { + struct rq *rq = cpu_rq(cpu); + struct task_struct *p; + + p = task_rcu_dereference(&rq->curr); + if (p && p->mm == mm) + __cpumask_set_cpu(cpu, tmpmask); + } + rcu_read_unlock(); + + preempt_disable(); + smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1); + preempt_enable(); + + free_cpumask_var(tmpmask); + cpus_read_unlock(); + + return 0; +} + static int membarrier_register_global_expedited(void) { struct task_struct *p = current; struct mm_struct *mm = p->mm; + int ret;
if (atomic_read(&mm->membarrier_state) & MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY) return 0; atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, &mm->membarrier_state); - if (atomic_read(&mm->mm_users) == 1) { - /* - * For single mm user, single threaded process, we can - * simply issue a memory barrier after setting - * MEMBARRIER_STATE_GLOBAL_EXPEDITED to guarantee that - * no memory access following registration is reordered - * before registration. - */ - smp_mb(); - } else { - /* - * For multi-mm user threads, we need to ensure all - * future scheduler executions will observe the new - * thread flag state for this mm. - */ - synchronize_sched(); - } + ret = sync_runqueues_membarrier_state(mm); + if (ret) + return ret; atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY, &mm->membarrier_state);
@@ -222,12 +311,15 @@ static int membarrier_register_private_expedited(int flags) { struct task_struct *p = current; struct mm_struct *mm = p->mm; - int state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY; + int ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY, + set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED, + ret;
if (flags & MEMBARRIER_FLAG_SYNC_CORE) { if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) return -EINVAL; - state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; + ready_state = + MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; }
/* @@ -235,20 +327,15 @@ static int membarrier_register_private_expedited(int flags) * groups, which use the same mm. (CLONE_VM but not * CLONE_THREAD). */ - if ((atomic_read(&mm->membarrier_state) & state) == state) + if ((atomic_read(&mm->membarrier_state) & ready_state) == ready_state) return 0; - atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED, &mm->membarrier_state); if (flags & MEMBARRIER_FLAG_SYNC_CORE) - atomic_or(MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE, - &mm->membarrier_state); - if (atomic_read(&mm->mm_users) != 1) { - /* - * Ensure all future scheduler executions will observe the - * new thread flag state for this process. - */ - synchronize_sched(); - } - atomic_or(state, &mm->membarrier_state); + set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE; + atomic_or(set_state, &mm->membarrier_state); + ret = sync_runqueues_membarrier_state(mm); + if (ret) + return ret; + atomic_or(ready_state, &mm->membarrier_state);
return 0; } @@ -262,8 +349,10 @@ static int membarrier_register_private_expedited(int flags) * command specified does not exist, not available on the running * kernel, or if the command argument is invalid, this system call * returns -EINVAL. For a given command, with flags argument set to 0, - * this system call is guaranteed to always return the same value until - * reboot. + * if this system call returns -ENOSYS or -EINVAL, it is guaranteed to + * always return the same value until reboot. In addition, it can return + * -ENOMEM if there is not enough memory available to perform the system + * call. * * All memory accesses performed in program order from each targeted thread * is guaranteed to be ordered with respect to sys_membarrier(). If we use diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 0c2fb4b..2213dac 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -843,6 +843,10 @@ struct rq {
atomic_t nr_iowait;
+#ifdef CONFIG_MEMBARRIER + int membarrier_state; +#endif + #ifdef CONFIG_SMP struct root_domain *rd; struct sched_domain *sd; @@ -2273,3 +2277,33 @@ unsigned long scale_irq_capacity(unsigned long util, unsigned long irq, unsigned return util; } #endif + +#ifdef CONFIG_MEMBARRIER +/* + * The scheduler provides memory barriers required by membarrier between: + * - prior user-space memory accesses and store to rq->membarrier_state, + * - store to rq->membarrier_state and following user-space memory accesses. + * In the same way it provides those guarantees around store to rq->curr. + */ +static inline void membarrier_switch_mm(struct rq *rq, + struct mm_struct *prev_mm, + struct mm_struct *next_mm) +{ + int membarrier_state; + + if (prev_mm == next_mm) + return; + + membarrier_state = atomic_read(&next_mm->membarrier_state); + if (READ_ONCE(rq->membarrier_state) == membarrier_state) + return; + + WRITE_ONCE(rq->membarrier_state, membarrier_state); +} +#else +static inline void membarrier_switch_mm(struct rq *rq, + struct mm_struct *prev_mm, + struct mm_struct *next_mm) +{ +} +#endif