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SubjectRe: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages
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> On Apr 6, 2019, at 11:08 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>
>> On Sat, 6 Apr 2019, Andy Lutomirski wrote:
>>> On Fri, Apr 5, 2019 at 8:11 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>>>
>>> From: Andy Lutomirski <luto@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.
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