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kernel: thread: Consider stack pointer fuzz underflow

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When randomizing the stack pointer on thread creation
(CONFIG_STACK_POINTER_RANDOM), the fuzz amount might exceed the stack
size, causing an underflow.

Ensure that this will never underflow by only adjusting the stack size
if there's enough space.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>
This commit is contained in:
Leandro Pereira 2018-04-03 09:47:41 -07:00 committed by Andrew Boie
parent 2486d5a2d2
commit 1ccd715577
1 changed files with 30 additions and 11 deletions
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41
kernel/thread.c
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@ -256,25 +256,44 @@ static void schedule_new_thread(struct k_thread *thread, s32_t delay)
}
#endif
void _setup_new_thread(struct k_thread *new_thread,
k_thread_stack_t *stack, size_t stack_size,
k_thread_entry_t entry,
void *p1, void *p2, void *p3,
int prio, u32_t options)
#if !CONFIG_STACK_POINTER_RANDOM
static inline size_t adjust_stack_size(size_t stack_size)
{
return stack_size;
}
#else
static inline size_t adjust_stack_size(size_t stack_size)
{
#if CONFIG_STACK_POINTER_RANDOM
#if defined(CONFIG_STACK_GROWS_UP)
/* This is so rare not bothering for now */
#error "Stack pointer randomization not implemented for upward growing stacks"
#endif
/* Don't need to worry about alignment of the size here, _new_thread()
* is required to do it
*
* FIXME: Not the best way to get a random number in a range.
* See #6493
*/
stack_size -= sys_rand32_get() % CONFIG_STACK_POINTER_RANDOM;
const size_t fuzz = sys_rand32_get() % CONFIG_STACK_POINTER_RANDOM;
if (unlikely(fuzz * 2 > stack_size)) {
return stack_size;
}
return stack_size - fuzz;
}
#if defined(CONFIG_STACK_GROWS_UP)
/* This is so rare not bothering for now */
#error "Stack pointer randomization not implemented for upward growing stacks"
#endif /* CONFIG_STACK_GROWS_UP */
#endif /* CONFIG_STACK_POINTER_RANDOM */
void _setup_new_thread(struct k_thread *new_thread,
k_thread_stack_t *stack, size_t stack_size,
k_thread_entry_t entry,
void *p1, void *p2, void *p3,
int prio, u32_t options)
{
stack_size = adjust_stack_size(stack_size);
_new_thread(new_thread, stack, stack_size, entry, p1, p2, p3,
prio, options);
#ifdef CONFIG_USERSPACE