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    SubjectRe: [PATCH] uprobes: Ignore unsupported instructions in uprobe_mmap
    > > uprobe_mmap()->install_breakpoint() can fail if the probed insn is not
    > > supported
    > But there are other reasons why it can fail,
    > > However failing mmap_region()/do_fork() because of a probe on an
    > > unsupported instruction is wrong.
    > Srikar, I strongly, absolutely disagree. Please correct me, but..
    > Do you realize how much uprobes hooks in mmap_region/dup_mmap are broken?
    > (cough, can't resist, vma_adjust()->uprobe_mmap() is not right too, but
    > this is another story).
    > OK, lets start with dup_mmap:
    > // retval == 0
    > if (file && uprobe_mmap(tmp))
    > goto out;
    > out:
    > up_write(&mm->mmap_sem);
    > flush_tlb_mm(oldmm);
    > up_write(&oldmm->mmap_sem);
    > return retval;
    > Given that retval == 0, what do you think dup_mmap() returns if
    > uprobe_mmap() fails? And note that we didn't copy all vmas.
    > OK, at least this can't crash (afaics), and easy to fix.
    > But mmap_region() is worse, much worse. It simply can _not_ fail
    > after uprobe_mmap (of course, I am not saying this is unfixable)
    > without the crash. And note that the crash is "delayed". And btw,
    > like dup_mmap(), mmap_region() doesn't return the error too.

    Oh, thats really a bad mistake from my side. I apologize.

    > Srikar, I strongly believe this horror must not exist. Either
    > we should teach mmap_region() and dup_mmap() (and vma_adjust!)
    > to fail correctly, or we should ignore the error code.
    > It is that simple, isn't it?


    > Whatever you do with uprobe_mmap(), even if you change it to always
    > return 0, the code in mmap_region() is absolutely, absolutely broken.

    But uprobe_mmap() still needs to walk thro the probe list and
    insert the other probes. Currently we just ignore the remaining probes
    and that has to be fixed within uprobe_mmap.

    > Do you agree?
    > And once again. I agree, in the long term we should reconsider
    > this change. But we need a simple fix for now/stable.


    > > Hence change uprobe_mmap() to ignore unsupported instructions.
    > OK. Now suppose that mmap_region()-> uprobe_mmap() fails because
    > the caller is SIGKILL'ed (so __get_user_pages fails). Given that
    > mmap_region() can't handle the error correctly, the kernel can
    > crash.

    How about having your fix + my patch to fix the uprobe_mmap()?

    Thanks and Regards

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      Last update: 2012-08-02 19:41    [W:0.027 / U:69.004 seconds]
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