> On Apr 7, 2019, at 2:34 AM, Thomas Gleixner <t...@linutronix.de> wrote: > > On Sun, 7 Apr 2019, Andy Lutomirski wrote: >>> On Apr 6, 2019, at 11:08 PM, Thomas Gleixner <t...@linutronix.de> wrote: >>> >>>>> On Sat, 6 Apr 2019, Andy Lutomirski wrote: >>>>> On Fri, Apr 5, 2019 at 8:11 AM Thomas Gleixner <t...@linutronix.de> wrote: >>>>> >>>>> From: Andy Lutomirski <l...@kernel.org> >>>>> >>>>> The IRQ stack lives in percpu space, so an IRQ handler that overflows it >>>>> will overwrite other data structures. >>>>> >>>>> Use vmap() to remap the IRQ stack so that it will have the usual guard >>>>> pages that vmap/vmalloc allocations have. With this the kernel will panic >>>>> immediately on an IRQ stack overflow. >>>> >>>> The 0day bot noticed that this dies with DEBUG_PAGEALLOC on. This is >>>> because the store_stackinfo() function is utter garbage and this patch >>>> correctly detects just how broken it is. The attached patch "fixes" >>>> it. (It also contains a reliability improvement that should probably >>>> get folded in, but is otherwise unrelated.) >>>> >>>> A real fix would remove the generic kstack_end() function entirely >>>> along with __HAVE_ARCH_KSTACK_END and would optionally replace >>>> store_stackinfo() with something useful. Josh, do we have a generic >>>> API to do a little stack walk like this? Otherwise, I don't think it >>>> would be the end of the world to just remove the offending code. >>> >>> Yes, I found the same yesterday before heading out. It's already broken >>> with the percpu stack because there is no guarantee that the per cpu stack >>> is thread size aligned. It's guaranteed to be page aligned not more. >>> >>> I'm all for removing that nonsense, but the real question is whether there >>> is more code which assumes THREAD_SIZE aligned stacks aside of the thread >>> stack itself. >>> >>> >> Well, any code like this is already busted, since the stacks alignment >> doesn’t really change with these patches applied. > > It does. The existing code has it aligned by chance because the irq stack > is the first entry in the per cpu area. But yes, there is no reason to require > that alignment for irqstacks. >
Isn’t it the first entry in the percpu area (the normal one, not cea)? Is that aligned beyond PAGE_SIZE?