On Thu, Nov 22, 2018 at 11:54 PM, Wang Dongsheng
<dongsheng.w...@hxt-semitech.com> wrote:
> When select ARCH_TASK_STRUCT_ON_STACK the first of thread_info variable
> is overwritten by STACK_END_MAGIC. In fact, the ARCH_TASK_STRUCT_ON_STACK
> is not a real task on stack, it's only init_task on init_stack.
>
> Commit 0500871f21b2 ("Construct init thread stack in the linker script
> rather than by union") added this macro and put task_strcut into
> thread_union. This brings us the following possibilities:
> TASK_ON_STACK THREAD_INFO_IN_TASK STACK
> ----- <-- thread_info & stack
> N N | | --- <-- task
> | | | |
> ----- ---
>
> ----- <-- stack
> N Y | | --- <-- task(Including
> thread_info)
> | | | |
> ----- ---
>
> ----- <-- stack & task &
> thread_info
> Y N | |
> | |
> -----
>
> ----- <-- stack & task(Including
> thread_info)
> Y Y | |
> | |
> -----
> The kernel has handled the first two cases correctly.
>
> For the third case:
> TASK_ON_STACK: Y. THREAD_INFO_IN_TASK: N. this case
> should never happen, because the task and thread_info will overlap. So
> when TASK_ON_STACK is selected, THREAD_INFO_IN_TASK must be selected too.
>
> For the fourth case:
> When task on stack, the end of stack should add a sizeof(task_struct) offset.
>
> This patch handled with the third and fourth case.
>
> Fixes: 0500871f21b2 ("Construct init thread stack in the linker ...")
>
> Signed-off-by: Wang Dongsheng <dongsheng.w...@hxt-semitech.com>
> Signed-off-by: Shunyong Yang <shunyong.y...@hxt-semitech.com>
> ---
> arch/Kconfig | 1 +
> include/linux/sched/task_stack.h | 5 ++++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index e1e540ffa979..0a2c73e73195 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -251,6 +251,7 @@ config ARCH_HAS_SET_MEMORY
> # Select if arch init_task must go in the __init_task_data section
> config ARCH_TASK_STRUCT_ON_STACK
> bool
> + depends on THREAD_INFO_IN_TASK || IA64
The "IA64" part shouldn't be needed since IA64 already selects it.
Since it's selected, it also can't have a depends, IIUC.
>
> # Select if arch has its private alloc_task_struct() function
> config ARCH_TASK_STRUCT_ALLOCATOR
> diff --git a/include/linux/sched/task_stack.h
> b/include/linux/sched/task_stack.h
> index 6a841929073f..624c48defb9e 100644
> --- a/include/linux/sched/task_stack.h
> +++ b/include/linux/sched/task_stack.h
> @@ -7,6 +7,7 @@
> */
>
> #include <linux/sched.h>
> +#include <linux/sched/task.h>
> #include <linux/magic.h>
>
> #ifdef CONFIG_THREAD_INFO_IN_TASK
> @@ -25,7 +26,9 @@ static inline void *task_stack_page(const struct
> task_struct *task)
>
> static inline unsigned long *end_of_stack(const struct task_struct *task)
> {
> - return task->stack;
> + if (!IS_ENABLED(CONFIG_ARCH_TASK_STRUCT_ON_STACK) || task !=
> &init_task)
> + return task->stack;
> + return (unsigned long *)(task + 1);
> }
This seems like a strange place for the change. It feels more like
init_task has been defined incorrectly.
-Kees
>
> #elif !defined(__HAVE_THREAD_FUNCTIONS)
> --
> 2.19.1
>
--
Kees Cook
