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    SubjectRe: [PATCH] mm: larger stack guard gap, between vmas
    On Tue, Jul 04, 2017 at 11:37:15AM -0700, Linus Torvalds wrote:
    > On Tue, Jul 4, 2017 at 10:22 AM, Michal Hocko <mhocko@kernel.org> wrote:
    > >
    > > Well, I've been thinking about this some more and the more I think about
    > > it the less I am convinced we should try to be clever here. Why? Because
    > > as soon as somebody tries to manage stacks explicitly you cannot simply
    > > assume anything about the previous mapping. Say some interpret uses
    > > [ mngmnt data][red zone] <--[- MAP_GROWSDOWN ]
    > >
    > > Now if we consider the red zone's (PROT_NONE) prev mapping we would fail
    > > the expansion even though we haven't hit the red zone and that is
    > > essentially what the Java and rust bugs are about. So we just risk yet
    > > another regression.
    >
    > Ack.
    >
    > Let's make the initial version at least only check the first vma.
    >
    > The long-term fix for this is to have the binaries do proper stack
    > expansion probing anyway, and it's quite possible that people who do
    > their own stack redzoning by adding a PROT_NONE thing already do that
    > proper fix (eg the Java stack may simply not *have* those big crazy
    > structures on it in the first place).

    But what is wrong with stopping the loop as soon as the distance gets
    larger than the stack_guard_gap ?

    Willy

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