Re: [PATCH v2] x86, kaslr: export offset in VMCOREINFO ELF notes

[Ingo Molnar <mingo@kernel.org>]

* Adrian Hunter <adrian.hunter@intel.com> wrote:

> On 25/01/14 09:47, Ingo Molnar wrote:
> > 
> > * Kees Cook <keescook@chromium.org> wrote:
> > 
> >> From: Eugene Surovegin <surovegin@google.com>
> >>
> >> Include kASLR offset in VMCOREINFO ELF notes to assist in debugging.
> >>
> >> Signed-off-by: Eugene Surovegin <surovegin@google.com>
> >> Signed-off-by: Kees Cook <keescook@chromium.org>
> >> ---
> >> v2:
> >>  - make sure "From:" got sent correctly
> >> ---
> >>  arch/x86/kernel/machine_kexec_64.c |    2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> >> index 4eabc160696f..679cef0791cd 100644
> >> --- a/arch/x86/kernel/machine_kexec_64.c
> >> +++ b/arch/x86/kernel/machine_kexec_64.c
> >> @@ -279,5 +279,7 @@ void arch_crash_save_vmcoreinfo(void)
> >>  	VMCOREINFO_SYMBOL(node_data);
> >>  	VMCOREINFO_LENGTH(node_data, MAX_NUMNODES);
> >>  #endif
> >> +	vmcoreinfo_append_str("KERNELOFFSET=%lx\n",
> >> +			      (unsigned long)&_text - __START_KERNEL);
> >>  }
> > 
> > I've Cc:-ed Adrian Hunter, who has sent the following kaslr fixes for 
> > perf yesterday:
> > 
> >   http://lkml.org/lkml/2014/1/24/220
> > 
> > Adrian, is this patch the right solution from the perf tooling 
> > perspective?
> 
> perf tools isn't a consumer of VMCOREINFO although I see VMCOREINFO 
> already has _stext which would be enough for many purposes.

Yes - but let me explain where I'm coming from: I'd like the recent 
KASLR related perf /proc/kcore based annotation bug to be fixed 
properly.

Currently I'm not sure about the status of it. In your fixes 
submission:

  Date: Fri, 24 Jan 2014 17:10:10 +0200
  From: Adrian Hunter <adrian.hunter@intel.com>
  Subject: [PATCH 0/8] perf tools: kaslr fixes

you mentioned the following:

    "- mustn't use kcore if the kernel has moved"

Does this that /proc/kcore annotation will not work if KASLR is 
active?

If yes then given that I expect most distros to turn on KASLR this 
would essentially make /proc/kcore useless on a large set of Linux 
systems. That would be suboptimal.

Thanks,

	Ingo