On 27/01/14 17:25, Ingo Molnar wrote:
>
> * Adrian Hunter <[email protected]> wrote:
>
>> On 25/01/14 09:47, Ingo Molnar wrote:
>>>
>>> * Kees Cook <[email protected]> wrote:
>>>
>>>> From: Eugene Surovegin <[email protected]>
>>>>
>>>> Include kASLR offset in VMCOREINFO ELF notes to assist in debugging.
>>>>
>>>> Signed-off-by: Eugene Surovegin <[email protected]>
>>>> Signed-off-by: Kees Cook <[email protected]>
>>>> ---
>>>> 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 <[email protected]>
> 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?
No. In fact annotation works now with kcore. Linus' problem was with vmlinux.
Kcore won't be used with kaslr in the case:
1. record data with 'perf record'
2. reboot
3. use annotation on the previously recorded data
As I noted in the commit message, you can still use kcore if you made a copy
(with perf buildid-cache) at the time the data was recorded.
>
> 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
>
>
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