lkml.org 
[lkml]   [2013]   [Nov]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH -tip v2 3/3] [BUGFIX] kprobes: Prohibit probing on func_ptr_is_kernel_text

    * Steven Rostedt <rostedt@goodmis.org> wrote:

    > On Fri, 01 Nov 2013 11:25:37 +0000
    > Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
    >
    > > Prohibit probing on func_ptr_is_kernel_text().
    > > Since the func_ptr_is_kernel_text() is called from
    > > notifier_call_chain() which is called from int3 handler,
    > > probing it may cause double int3 fault and kernel will
    > > reboot.
    > >
    > > This happenes when the kernel built with CONFIG_DEBUG_NOTIFIERS=y.
    > >
    > > Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    > > Cc: Andrew Morton <akpm@linux-foundation.org>
    > > Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
    > > Cc: Borislav Petkov <bp@suse.de>
    > > Cc: Ingo Molnar <mingo@kernel.org>
    > > ---
    > > kernel/extable.c | 2 +-
    > > 1 file changed, 1 insertion(+), 1 deletion(-)
    > >
    > > diff --git a/kernel/extable.c b/kernel/extable.c
    > > index 832cb28..022fb25 100644
    > > --- a/kernel/extable.c
    > > +++ b/kernel/extable.c
    > > @@ -129,7 +129,7 @@ int kernel_text_address(unsigned long addr)
    > > * pointer is part of the kernel text, we need to do some
    > > * special dereferencing first.
    > > */
    > > -int func_ptr_is_kernel_text(void *ptr)
    > > +int nokprobe func_ptr_is_kernel_text(void *ptr)
    > > {
    > > unsigned long addr;
    > > addr = (unsigned long) dereference_function_descriptor(ptr);
    > >
    >
    > One thing I worry about the "nokprobe" annotation, is that it moves the
    > location of the function out of local. This function no exists in the
    > section with its users. Same with the debug functions in the other
    > patch.

    Well, it's a bit like noinline, that changes the position of the function
    as well. So it's not true that 'noxyz' attributes don't affect function
    placement - they often don't, but some do.

    The more important aspect is that 'noprobe' makes it really, really
    apparent what the tag is about, at first sight.

    _How_ the 'non probing' is achived is an implementational detail when
    kprobes are enabled: right now it puts a function into a separate section,
    but we could just a much build a list of function names and check against
    it at probe insertion time.

    Thanks,

    Ingo
    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2013-11-05 07:21    [W:4.054 / U:0.168 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site