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Subject[PATCH 4.4 2/7] sched/core: Add try_get_task_stack() and put_task_stack()
Date
From: Andy Lutomirski <luto@kernel.org>

commit c6c314a613cd7d03fb97713e0d642b493de42e69 upstream.

There are a few places in the kernel that access stack memory
belonging to a different task. Before we can start freeing task
stacks before the task_struct is freed, we need a way for those code
paths to pin the stack.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/17a434f50ad3d77000104f21666575e10a9c1fbd.1474003868.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
---
include/linux/sched.h | 16 ++++++++++++++++
init/Kconfig | 3 +++
2 files changed, 19 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d6b2e77aad3f..761247c966a5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2858,11 +2858,19 @@ static inline struct thread_info *task_thread_info(struct task_struct *task)
{
return &task->thread_info;
}
+
+/*
+ * When accessing the stack of a non-current task that might exit, use
+ * try_get_task_stack() instead. task_stack_page will return a pointer
+ * that could get freed out from under you.
+ */
static inline void *task_stack_page(const struct task_struct *task)
{
return task->stack;
}
+
#define setup_thread_stack(new,old) do { } while(0)
+
static inline unsigned long *end_of_stack(const struct task_struct *task)
{
return task->stack;
@@ -2898,6 +2906,14 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
}

#endif
+
+static inline void *try_get_task_stack(struct task_struct *tsk)
+{
+ return task_stack_page(tsk);
+}
+
+static inline void put_task_stack(struct task_struct *tsk) {}
+
#define task_stack_end_corrupted(task) \
(*(end_of_stack(task)) != STACK_END_MAGIC)

diff --git a/init/Kconfig b/init/Kconfig
index 5dec7d424980..f9fb621c9562 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -33,6 +33,9 @@ config THREAD_INFO_IN_TASK
make this work, an arch will need to remove all thread_info fields
except flags and fix any runtime bugs.

+ One subtle change that will be needed is to use try_get_task_stack()
+ and put_task_stack() in save_thread_stack_tsk() and get_wchan().
+
menu "General setup"

config BROKEN
--
2.17.2
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