[Makedumpfile PATCH 0/2] Fix refiltering when kaslr enabled

[Atsushi Kumagai]

>On Tuesday 23 May 2017 08:39 AM, Atsushi Kumagai wrote:
>>>>>>>> Thanks for your report, I have received this.
>>>>>>>> I'm on vacation until Mar 8, I'll review it when I return from vacation.
>>>>>>>
>>>>>>> Any further comment on it?
>>>>>>> Otherwise, I will send a v2 after accommodating concern from Xunlei.
>>>>>>
>>>>>> Unfortunately, it doesn't seem like I can make time anymore for review this week,
>>>>>> but at least this patch doesn't seem to work in my environment (linux 4.8 without kaslr).
>>>>>> Do you have any ideas ?
>>>>>
>>>>> I see, why it would have caused. I have not tested this case, but I hope my v2
>>>>> should not have this issue.
>>>>
>>>> Umm, v2 still doesn't work in my environment...
>>>> It seems that I have to investigate this deeper.
>>>
>>> Hummm, I thought we would see file_vmcoreinfo as NULL in
>>> get_kaslr_offset_x86_64() in your case. However, it's not true.
>>>
>>> I think, it will have to be initialized with NULL in main().
>>>
>>> Can you please try following fixup on top of this series:
>>
>> I found the cause, please see below:
>>
>> initial()
>>   + find_kaslr_offsets()
>>     + open_vmcoreinfo()
>>     + get_kaslr_offset()        // set info->kaslr_offset
>>     + close_vmcoreinfo()
>> gather_filter_info()
>>   (snip)
>>   + resolve_config_entry()
>>     + get_kaslr_offset()        // occur SIGSEGV since info->file_vmcoreinfo is closed
>
>Since info->file_vmcoreinfo is closed,therefore it should be NULL. But
>currently, close_vmcoreinfo() does not set it to NULL. We should also set
>info->file_vmcoreinfo to NULL in close_vmcoreinfo() apart from main().

Sure, uninitialized info->file_vmcoreinfo is a general issue,
I'll fix it in another patch.

>>
>>
>> The cause code is in [PATCH v2 1/2],
>>
>> diff --git a/erase_info.c b/erase_info.c
>> index f2ba914..60abfa1 100644
>> --- a/erase_info.c
>> +++ b/erase_info.c
>> @@ -1088,6 +1088,7 @@ resolve_config_entry(struct config_entry *ce, unsigned long long base_vaddr,
>>                                                         ce->line, ce->name);
>>                         return FALSE;
>>                 }
>> +               ce->sym_addr += get_kaslr_offset(ce->sym_addr);
>>                 ce->type_name = get_symbol_type_name(ce->name,
>>                                         DWARF_INFO_GET_SYMBOL_TYPE,
>>                                         &ce->size, &ce->type_flag);
>>
>>
>> I think we should use info->kaslr_offset instead of get_kaslr_offset(),
>> how about you ?
>
>Actually,  we are not sure at this point that ce->sym_addr is a kernel linear
>address. It could be a module address and that can have different
>randomization offset.

I see, I misunderstood that the randomization offset is same in any case.

>My intention is to calculate all types of kaslr offsets in
>find_kaslr_offsets() very early and then store them in different "info"
>elements. Now, whenever we call get_kaslr_offset() we would return right
>offset as per the input address.
>I have very little idea about x86. So, I have left a TODO to calculate offset
>for non-linear addresses.
>
>>
>> BTW, I'm not sure why you didn't meet this issue...
>
>Because, I tested with kaslr kernel, so when get_kaslr_offset(ce->sym_addr)
>was called, I already had a valid info->kaslr_offset.
>
>So, what about following fixup

As mentioned at the beginning, the fix below is not your fault,
so I'll merge your patches as it is into v1.6.2.

>diff --git a/makedumpfile.c b/makedumpfile.c
>index 57235690569e..4986d098d69a 100644
>--- a/makedumpfile.c
>+++ b/makedumpfile.c
>@@ -8685,6 +8685,7 @@ close_vmcoreinfo(void)
>         if(fclose(info->file_vmcoreinfo) < 0)
>                 ERRMSG("Can't close the vmcoreinfo file(%s). %s\n",
>                     info->name_vmcoreinfo, strerror(errno));
>+       info->file_vmcoreinfo = NULL;
>  }
>
>  void
>@@ -11076,6 +11077,7 @@ main(int argc, char *argv[])
>                     strerror(errno));
>                 goto out;
>         }
>+       info->file_vmcoreinfo = NULL;
>         info->fd_vmlinux = -1;
>         info->fd_xen_syms = -1;
>         info->fd_memory = -1;

However, I think [PATCH 2/2] should be dropped since the alternative patch
has appeared, is it ok with you ?

https://github.com/pratyushanand/makedumpfile/commit/16655ce1f4c2da8d4066072db2a03c84bf2553fe

Thanks,
Atsushi Kumagai

>
>~Pratyush
>
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