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    SubjectRe: [PATCH v26 22/30] x86/cet/shstk: Add user-mode shadow stack support
    On Thu, Apr 29, 2021 at 09:17:06AM -0700, Yu, Yu-cheng wrote:
    > The lock applies to both shadow stack and ibt. So maybe just "locked"?

    Sure.

    > vm_munmap() returns error as the following:
    >
    > (1) -EINVAL: address/size/alignment is wrong.
    > For shadow stack, the kernel keeps track of it, this cannot/should not
    > happen.

    You mean nothing might corrupt

    cet->shstk_base
    cet->shstk_size

    ?

    I can't count the ways I've heard "should not happen" before and then it
    happening anyway.

    So probably not but we better catch stuff like that instead of leaking.

    > Should it happen, it is a bug.

    Ack.

    > The kernel can probably do WARN().

    Most definitely WARN. You need to catch funsies like that. But WARN_ONCE
    should be enough for now.

    > (2) -ENOMEM: when doing __split_vma()/__vma_adjust(), kmem_cache_alloc()
    > fails.
    > Not much we can do. Perhaps WARN()?

    You got it.

    Bottom line is: if you can check for this and it is cheap, then
    definitely. Code changes, gets rewritten, reorganized, the old
    assertions change significance, and so on...

    Thx.

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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