Messages in this thread | | | Date | Tue, 2 Apr 2019 09:34:26 -0700 | From | Sean Christopherson <> | Subject | Re: [patch 01/14] x86/irq/64: Limit IST stack overflow check to #DB stack |
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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 <tglx@linutronix.de> > Cc: Mitsuo Hayasaka <mitsuo.hayasaka.hu@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; > > >
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