On Sun, Mar 31, 2019 at 11:40:21PM +0200, Thomas Gleixner wrote:
> 37fe6a42b343 ("x86: Check stack overflow in detail") added a broad check
> for the full exception stack area, i.e. it considers the full exception
> stack are as valid.
^^^
area
>
> That's wrong in two aspects:
>
> 1) It does not check the individual areas one by one
>
> 2) #DF, NMI and #MCE are not enabling interrupts which means that a
> regular device interrupt cannot happen in their context. In fact if a
> device interrupt hits one of those IST stacks that's a bug because some
> code path enabled interrupts while handling the exception.
>
> Limit the check to the #DB stack and consider all other IST stacks as
> 'overflow' or invalid.
>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
> Cc: Mitsuo Hayasaka <mitsuo.hayasaka...@hitachi.com>
> ---
> arch/x86/kernel/irq_64.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> --- a/arch/x86/kernel/irq_64.c
> +++ b/arch/x86/kernel/irq_64.c
> @@ -26,9 +26,18 @@ int sysctl_panic_on_stackoverflow;
> /*
> * Probabilistic stack overflow check:
> *
> - * Only check the stack in process context, because everything else
> - * runs on the big interrupt stacks. Checking reliably is too expensive,
> - * so we just check from interrupts.
> + * Regular device interrupts can enter on the following stacks:
> + *
> + * - User stack
> + *
> + * - Kernel task stack
> + *
> + * - Interrupt stack if a device driver reenables interrupt
> + * which should only happen in really old drivers.
> + *
> + * - Debug IST stack
> + *
> + * All other contexts are invalid.
> */
> static inline void stack_overflow_check(struct pt_regs *regs)
> {
> @@ -53,8 +62,8 @@ static inline void stack_overflow_check(
> return;
>
> oist = this_cpu_ptr(&orig_ist);
> - estack_top = (u64)oist->ist[0] - EXCEPTION_STKSZ + STACK_TOP_MARGIN;
> - estack_bottom = (u64)oist->ist[N_EXCEPTION_STACKS - 1];
> + estack_bottom = (u64)oist->ist[DEBUG_STACK];
> + estack_top = estack_bottom - DEBUG_STKSZ + STACK_TOP_MARGIN;
> if (regs->sp >= estack_top && regs->sp <= estack_bottom)
> return;
>
>
>
