linux-kernel - Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages

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Date:   Sat, 6 Apr 2019 21:56:21 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages

On Fri, Apr 5, 2019 at 8:11 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> From: Andy Lutomirski <luto@...nel.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.

--Andy

View attachment "fix.diff" of type "text/x-patch" (1968 bytes)