Re: [PATCH & RFC] kdump and stack overflows

From: Fernando Luis Vazquez Cao (fernando_at_intellilink.co.jp)
Date: 11/29/05

  • Next message: Randy.Dunlap: "Re: saa7134 broken in 2.6.15-rc2" 
    To: "Eric W. Biederman" <ebiederm@xmission.com>
Date:	Wed, 30 Nov 2005 00:43:32 +0900

    On Mon, 2005-11-28 at 11:29 -0700, Eric W. Biederman wrote:
    > Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes:
    >
    > > On Mon, 2005-11-28 at 06:39 -0700, Eric W. Biederman wrote:
    > >> Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes:
    >
    > > Regarding the stack overflow audit of the nmi path, we have the problem
    > > that both nmi_enter and nmi_exit in do_nmi (see code below) make heavy
    > > use of "current" indirectly (specially through the kernel preemption
    > > code).
    >
    > Ok. I wonder if it would be saner to simply replace the nmi trap
    > handler on the crash dump path?
    That seems to be the cleanest way to solve the problem. I will write a
    patch implementing that and see how it works.

    > >> I believe we have a separate interrupt stack that
    > >> should help but..
    > > Yes, when using 4K stacks we have a separate interrupt stack that should
    > > help, but I am afraid that crash dumping is about being paranoid.
    >
    > Oh I agree. If we had a private 4K stack for the nmi handler we
    > would not need to worry about overflow in that case. (baring
    > nmi happening during nmis) Hmm. Is there anything to keep
    > us doing something bad in that case?
    I think that is a sensible thing to do. I am just back from a day
    off, but tomorrow I will take a closer look at this.

    Regards,

    Fernando

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