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

Atsushi Kumagai ats-kumagai at wm.jp.nec.com
Wed May 10 01:07:21 PDT 2017

>Hi Atsushi,
>On Friday 28 April 2017 12:22 PM, Atsushi Kumagai wrote:
>> Hello Pratyush,
>> 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 ?

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff6be49f5 in fseek () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install bzip2-libs-1.0.6-13.el7.x86_64 elfutils-libelf-0.163-3.el7.x86_64 elfutils-libs-0.163-3.el7.x86_64 glibc-2.17-105.el7.x86_64 libgcc-4.8.5-4.el7.x86_64 libstdc++-4.8.5-4.el7.x86_64 snappy-1.1.0-3.el7.x86_64 xz-libs-5.1.2-12alpha.el7.x86_64 zlib-1.2.7-15.el7.x86_64
(gdb) bt
#0  0x00007ffff6be49f5 in fseek () from /lib64/libc.so.6
#1  0x0000000000429d38 in read_vmcoreinfo_symbol (str_symbol=0x44cb0c "SYMBOL(_stext)=") at makedumpfile.c:2384
#2  0x000000000042097a in get_kaslr_offset_x86_64 (vaddr=18446744071589596288) at arch/x86_64.c:45
#3  0x0000000000414310 in resolve_config_entry (ce=0x701370, base_vaddr=<optimized out>, base_struct_name=0x0)
    at erase_info.c:1091
#4  0x0000000000415a89 in get_config_symbol_addr (base_struct_name=0x0, base_vaddr=0, ce=0x701370) at erase_info.c:1264
#5  update_filter_info (filter_symbol=0x701370, size_symbol=0x701430) at erase_info.c:1579
#6  0x0000000000416543 in process_config (config=<optimized out>) at erase_info.c:1789
#7  process_config_file (name_config=<optimized out>) at erase_info.c:1862
#8  0x0000000000417c57 in gather_filter_info () at erase_info.c:2356
#9  0x0000000000443ccb in create_dumpfile () at makedumpfile.c:9863
#10 0x000000000044561e in main (argc=<optimized out>, argv=<optimized out>) at makedumpfile.c:11342

Atsushi Kumagai

>> Thanks,
>> Atsushi Kumagai
>>> Hi All,
>>> We came across another failure in makedumpfile when kaslr is enabled. This
>>> failure occurs when we try re-filtering. We try to erase some symbol from a
>>> dumpfile which was copied/compressed from /proc/vmcore using makedumpfile.
>>> We have very limited symbol information in vmcoreinfo. So symbols to be
>>> erased may not be available in vmcoreinfo and we look for it in vmlinux.
>>> However,  symbol address from vmlinux is a static address which differs
>>>from run time address with KASLR_OFFSET. Therefore, reading any "virtual
>>> address of vmlinux" from vmcore is not possible.
>>> These patches finds runtime  KASLR offset and then calculates run time
>>> address of symbols read from vmlinux.
>>> Since, I am not an expert of x86, and these patches touch x86 part of
>>> makedumpfile, therefore I have CCed x86 experts. Please, provide your
>>> review comment and let me know if you think there could have been a better
>>> way to resolve this issue.
>>> thanks
>>> ~Pratyush
>>> Pratyush Anand (2):
>>>  makedumpfile: add runtime kaslr offset if it exists
>>>  x86_64: calculate page_offset in case of re-filtering
>>> arch/x86_64.c  | 45 +++++++++++++++++++++++++++++++++++++++++++--
>>> erase_info.c   |  1 +
>>> makedumpfile.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>>> makedumpfile.h | 15 +++++++++++++++
>>> 4 files changed, 103 insertions(+), 2 deletions(-)
>>> --
>>> 2.9.3

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