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    SubjectRe: [PATCH] x86: KPROBE_ENTRY should be paired wth KPROBE_END

    * Cyrill Gorcunov <gorcunov@gmail.com> wrote:

    > [Cyrill Gorcunov - Sun, Nov 23, 2008 at 04:51:34PM +0300]
    > | [Ingo Molnar - Sun, Nov 23, 2008 at 02:27:52PM +0100]
    > | |
    > | | * Alexander van Heukelum <heukelum@mailshack.com> wrote:
    > | |
    > | | > Impact: moves some code out of .kprobes.text
    > | | >
    > | | > KPROBE_ENTRY switches code generation to .kprobes.text, and KPROBE_END
    > | | > uses .popsection to get back to the previous section (.text, normally).
    > | | > Also replace ENDPROC by END, for consistency.
    > | | >
    > | | > Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
    > | |
    > | | applied to tip/x86/irq, thanks Alexander!
    > | |
    > | | > One more small change for today. The xen-related functions
    > | | > xen_do_hypervisor_callback and xen_failsafe_callback are put
    > | | > in the .kprobes.text even in the current kernel: ignore_sysret
    > | | > is enclosed in KPROBE_ENTRY / ENDPROC, instead of KPROBE_ENTRY /
    > | | > KPROBE_END, but I guess the situation is harmless.
    > | |
    > | | yeah. It narrows no-kprobes protection for that code, but it should
    > | | indeed be fine (and that's the intention as well).
    > | |
    > | | Note that this is a reoccuring bug type, and rather long-lived. Can
    > | | you think of any way to get automated nesting protection of both the
    > | | .cfi_startproc/endproc macros and kprobes start/end? A poor man's
    > | | solution would be to grep the number of start and end methods and
    > | | enforce that they are equal.
    > | |
    > | | Ingo
    > | |
    > |
    > | I think we could play with preprocessor and check if ENTRY/END matches.
    > | Looking now.
    > |
    > | - Cyrill -
    >
    > Here is what I've done
    >
    > 1) Add some macros like:
    >
    > .macro __set_entry
    > .set _ENTRY_IN, 1
    > .endm
    >
    > .macro __unset_entry
    > .set _ENTRY_IN, 0
    > .endm
    >
    > .macro __check_entry
    > .ifeq _ENTRY_IN
    > .error "END should be used"
    > .abort
    > .endif
    > .endm
    >
    > So the code
    >
    > ENTRY(mcount)
    > __unset_entry
    > retq
    > __check_entry
    > END(mcount)
    >
    > will fail like
    >
    > cyrill@lenovo linux-2.6.git $ make arch/x86/kernel/entry_64.o
    > CHK include/linux/version.h
    > CHK include/linux/utsrelease.h
    > SYMLINK include/asm -> include/asm-x86
    > CALL scripts/checksyscalls.sh
    > AS arch/x86/kernel/entry_64.o
    > arch/x86/kernel/entry_64.S: Assembler messages:
    > arch/x86/kernel/entry_64.S:84: Error: END should be used
    > arch/x86/kernel/entry_64.S:84: Fatal error: .abort detected. Abandoning ship.
    > make[1]: *** [arch/x86/kernel/entry_64.o] Error 1
    > make: *** [arch/x86/kernel/entry_64.o] Error 2
    > cyrill@lenovo linux-2.6.git $
    >
    > So if such an approach is acceptable (in general) -- I could take a
    > more deeper look. So every ENTRY would check if other ENTRY/KPROBE
    > is active and report that.

    looks good!

    Can we somehow detect a missing .cfi_endproc? That's another pattern
    i've seen.

    Ingo


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