Messages in this thread | | | Date | Thu, 14 Oct 2021 19:16:43 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] x86/unwind/orc: Handle kretprobes_trampoline |
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On Wed, 13 Oct 2021 21:52:36 -0700 Kees Cook <keescook@chromium.org> wrote:
> On Wed, Oct 13, 2021 at 06:41:01PM -0700, Josh Poimboeuf wrote: > > On Mon, Oct 11, 2021 at 02:03:26PM -0700, Kees Cook wrote: > > > On Thu, Sep 02, 2021 at 07:13:26PM -0700, Kees Cook wrote: > > > > From: Marios Pomonis <pomonis@google.com> > > > > > > > > Fix a bug in the ORC unwinder when kretprobes has replaced a return > > > > address with the address of `kretprobes_trampoline'. ORC mistakenly > > > > assumes that the address in the stack is a return address and decrements > > > > it by 1 in order to find the proper depth of the next frame.
Hmm, with my fixes[1], the kretprobe_trampoline address in the stack will be replaced with the correct return address. In that case, that behavior sounds correct.
[1] https://lore.kernel.org/all/163163030719.489837.2236069935502195491.stgit@devnote2/
> > > > > > > > This issue was discovered while testing the FG-KASLR series[0][1] and > > > > running the live patching test[2] that was originally failing[3]. > > > > > > > > [0] https://lore.kernel.org/kernel-hardening/20200923173905.11219-1-kristen@linux.intel.com/ > > > > [1] https://github.com/KSPP/linux/issues/132 > > > > [2] https://github.com/lpechacek/qa_test_klp > > > > [3] https://lore.kernel.org/lkml/alpine.LSU.2.21.2009251450260.13615@pobox.suse.cz/ > > > > > > > > Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder") > > > > Signed-off-by: Marios Pomonis <pomonis@google.com> > > > > Cc: Josh Poimboeuf <jpoimboe@redhat.com> > > > > Cc: Alexander Lobakin <alexandr.lobakin@intel.com> > > > > Cc: Kristen C Accardi <kristen.c.accardi@intel.com> > > > > Cc: Sami Tolvanen <samitolvanen@google.com> > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > Ping again; Josh can you take this please? > > > > I'm confused how this still fixes anything after Masami's patch set, > > which is now in linux-next. > > > > After those patches, for a CALL-type ORC entry, the unwinder sets > > state->ip to the address returned by unwind_recover_ret_addr(). In the > > case of a kretprobe, that means that state->ip will no longer point to > > kretprobes_trampoline() -- making the above patch description incorrect. > > > > Instead, state->ip will then contain the original call return address > > which was replaced by kretpobes. So it looks to the unwinder like a > > normal call return address, and 'state->signal' should remain false. > > > > Am I missing something? > > I'll let Marios answer in more detail, but my understanding is that > Masami's patch set didn't solve the FGKASLR-vs-kretprobes issue[1]. > I don't understand _why_ yet, though.
My another question is that this fix still works correctly on my series, because it's already merged via Steve's tree. Isn't this break anything?
I also need to know how (from where) the failed test uses stacktrace. Does it call stacktrace from outside of kretprobe?
Thank you,
> > -Kees > > [1] https://lore.kernel.org/all/CAKXAmdgS3SL_qyjzjY32_DXe3WVTN+O=wYwJ9vkUXKhjmt87fA@mail.gmail.com/ > > -- > Kees Cook
-- Masami Hiramatsu <mhiramat@kernel.org>
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