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userspace: treat thread stacks as kernel objects

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We need to track permission on stack memory regions like we do
with other kernel objects. We want stacks to live in a memory
area that is outside the scope of memory domain permission
management. We need to be able track what stacks are in use,
and what stacks may be used by user threads trying to call
k_thread_create().

Some special handling is needed because thread stacks appear as
variously-sized arrays of struct _k_thread_stack_element which is
just a char. We need the entire array to be considered an object,
but also properly handle arrays of stacks.

Validation of stacks also requires that the bounds of the stack
are not exceeded. Various approaches were considered. Storing
the size in some header region of the stack itself would not allow
the stack to live in 'noinit'. Having a stack object be a data
structure that points to the stack buffer would confound our
current APIs for declaring stacks as arrays or struct members.
In the end, the struct _k_object was extended to store this size.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
This commit is contained in:
Andrew Boie 2017-10-15 14:17:48 -07:00 • committed by Andrew Boie
commit bca15da650
7 changed files with 105 additions and 59 deletions
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46
include/kernel.h
View file

@ -142,6 +142,7 @@ enum k_objects {
K_OBJ_STACK,
K_OBJ_THREAD,
K_OBJ_TIMER,
K_OBJ__THREAD_STACK_ELEMENT,
/* Driver subsystems */
K_OBJ_DRIVER_ADC,
@ -177,6 +178,7 @@ struct _k_object {
u8_t perms[CONFIG_MAX_THREAD_BYTES];
u8_t type;
u8_t flags;
u32_t data;
} __packed;
#define K_OBJ_FLAG_INITIALIZED BIT(0)
@ -261,6 +263,26 @@ __syscall void k_object_access_revoke(void *object, struct k_thread *thread);
*/
void k_object_access_all_grant(void *object);
/* Using typedef deliberately here, this is quite intended to be an opaque
* type. K_THREAD_STACK_BUFFER() should be used to access the data within.
*
* The purpose of this data type is to clearly distinguish between the
* declared symbol for a stack (of type k_thread_stack_t) and the underlying
* buffer which composes the stack data actually used by the underlying
* thread; they cannot be used interchangably as some arches precede the
* stack buffer region with guard areas that trigger a MPU or MMU fault
* if written to.
*
* APIs that want to work with the buffer inside should continue to use
* char *.
*
* Stacks should always be created with K_THREAD_STACK_DEFINE().
*/
struct __packed _k_thread_stack_element {
char data;
};
typedef struct _k_thread_stack_element *k_thread_stack_t;
/* timeouts */
struct _timeout;
@ -422,6 +444,8 @@ struct k_thread {
#if defined(CONFIG_USERSPACE)
/* memory domain info of the thread */
struct _mem_domain_info mem_domain_info;
/* Base address of thread stack */
k_thread_stack_t stack_obj;
#endif /* CONFIG_USERSPACE */
/* arch-specifics: must always be at the end */
@ -511,28 +535,6 @@ extern void k_call_stacks_analyze(void);
/* end - thread options */
#if !defined(_ASMLANGUAGE)
/* Using typedef deliberately here, this is quite intended to be an opaque
* type. K_THREAD_STACK_BUFFER() should be used to access the data within.
*
* The purpose of this data type is to clearly distinguish between the
* declared symbol for a stack (of type k_thread_stack_t) and the underlying
* buffer which composes the stack data actually used by the underlying
* thread; they cannot be used interchangably as some arches precede the
* stack buffer region with guard areas that trigger a MPU or MMU fault
* if written to.
*
* APIs that want to work with the buffer inside should continue to use
* char *.
*
* Stacks should always be created with K_THREAD_STACK_DEFINE().
*/
struct __packed _k_thread_stack_element {
char data;
};
typedef struct _k_thread_stack_element *k_thread_stack_t;
/**
* @brief Create a thread.
*