[Crash-utility] [PATCH v2 0/2] Fix KASLR problem on sadump

[Dave Anderson]

Hi Takao,

A couple things.  Can you post against the current github sources,
or at least use crash-7.2.0?  I'm not sure what version you're 
working with:
  
  $ patch -p1 --dry-run < $dl/sadump_1.patch
  checking file defs.h
  Hunk #1 succeeded at 5629 (offset 7 lines).
  checking file x86_64.c
  Hunk #1 FAILED at 119.
  Hunk #2 succeeded at 1998 (offset 34 lines).
  Hunk #3 succeeded at 2016 (offset 34 lines).
  Hunk #4 succeeded at 2030 (offset 34 lines).
  Hunk #5 succeeded at 2086 (offset 34 lines).
  1 out of 5 hunks FAILED
  $ patch -p1 --dry-run < $dl/sadump_2.patch
  checking file defs.h
  Hunk #1 succeeded at 2590 (offset 5 lines).
  Hunk #2 succeeded at 6312 (offset 47 lines).
  checking file sadump.c
  checking file sadump.h
  checking file symbols.c
  Hunk #3 succeeded at 12262 (offset 10 lines).
  $
   
It was easy enough to address the FAILED segment above,
but there are a few issues with the sadump.c patch:  
  
  $ make warn
  ... [ cut ] ...
  cc -c -g -DX86_64 -DLZO -DSNAPPY -DGDB_7_6  sadump.c -Wall -O2 -Wstrict-prototypes -Wmissing-prototypes -fstack-protector -Wformat-security 
  sadump.c:1911:1: warning: no previous prototype for ‘get_kaslr_offset_from_vmcoreinfo’ [-Wmissing-prototypes]
   get_kaslr_offset_from_vmcoreinfo(ulong cr3, ulong orig_kaslr_offset,
   ^
  sadump.c: In function ‘sadump_calc_kaslr_offset’:
  sadump.c:2088:38: warning: ‘scs.Cr3’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (get_kaslr_offset_from_vmcoreinfo(
                                        ^
  sadump.c:2044:40: warning: ‘scs.IdtLower’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    idtr = ((uint64_t)scs.IdtUpper)<<32 | (uint64_t)scs.IdtLower;
                                          ^
  sadump.c:2044:10: warning: ‘scs.IdtUpper’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    idtr = ((uint64_t)scs.IdtUpper)<<32 | (uint64_t)scs.IdtLower;
  ...

But more importantly, the sadump.c patch won't compile against the 
other architectures, because x86_64_kvtop_pagetable() only exists 
when crash is built for x86_64.

Plus I don't particularly like the kvtop "pagetable" argument abstraction
and new functions that you put in place in x86_64.c just for these 3 rather
arcane calls from sadump.c.

I suggest adding a new machdep->flags bit (USE_PT?) which could 
be temporarily set in sadump.c prior to each of the 3 calls that 
could be made to the generic kvtop() function.  Then in x86_64_kvtop(),
check for the new machdep->flag as opposed to the "use_pagetable" argument.
It may even be possible to use SADUMP() along with some other existing 
flag instead of creating a new one.  But please just avoid creating the 
new functions in x86_64.c.

Thanks,
  Dave



----- Original Message -----
> Hi Dave, Hatayama-san,
> 
> Hatayama-san, thanks for your review, I updated may patch.
> 
> These patch series fix a problem that crash cannot open a dumpfile which is
> captured by sadump on KASLR enabled kernel.
> 
> When KASLR feature is enabled, a kernel is placed on the memory randomly and
> therefore crash cannot open a dumpfile because addresses of kernel symbols in
> vmlinux are different from actual addresses. In the case of kdump,
> information
> to get actual address is included in the vmcoreinfo, but dumpfile of sadump
> does
> not have such a information.
> 
> These patches calculate kaslr offset and phys_base to solve this problem. The
> basic idea is getting register (IDTR and CR3) from dump header, and calculate
> kaslr_offset/phys_base using them.
> 
> changelog:
> v2:
> - Remove virsh-dump part
> - Change get_vec0_addr style
> - Some tiny fixes
> 
> v1:
> https://www.redhat.com/archives/crash-utility/2017-October/msg00004.html
> 
> Takao Indoh (2):
>   Introduce x86_64_kvtop_pagetable
>   Fix a KASLR problem of sadump
> 
>  defs.h    |   5 +
>  sadump.c  | 458
>  +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  sadump.h  |   1 +
>  symbols.c |  34 +++++
>  x86_64.c  |  26 +++-
>  5 files changed, 522 insertions(+), 2 deletions(-)
> 
> --
> 2.9.5
> 
> 
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