[MAKEDUMPFILE PATCH] makedumpfile: elf_info: check for invalid physical address when finding max_paddr

[Coiby Xu]

On Thu, Jun 17, 2021 at 03:28:10AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
>-----Original Message-----
>>
>> Kernel commit 464920104bf7adac12722035bfefb3d772eb04d8
>> "/proc/kcore: update physical address for kcore ram and text" sets an
>> invalid paddr (-1=0xffffffffffffffff) for PT_LOAD segments of not direct
>> mapped regions,
>>     $ readelf -l /proc/kcore
>>
>>     Elf file type is CORE (Core file)
>>     Entry point 0x0
>>     There are 4 program headers, starting at offset 64
>>
>>     Program Headers:
>>       Type           Offset             VirtAddr           PhysAddr
>>                      FileSiz            MemSiz              Flags  Align
>>       NOTE           0x0000000000000120 0x0000000000000000 0x0000000000000000
>>                      0x0000000000002320 0x0000000000000000         0x0
>>       LOAD           0x1000000000010000 0xd000000000000000 0xffffffffffffffff
>>                                                            ^^^^^^^^^^^^^^^^^^
>>                      0x0001f80000000000 0x0001f80000000000  RWE    0x10000
>>       LOAD           0x0000000000010000 0xc000000000000000 0x0000000000000000
>>                      0x00000003f0000000 0x00000003f0000000  RWE    0x10000
>>       LOAD           0x3000000000010000 0xf000000000000000 0xffffffffffffffff
>>                                                            ^^^^^^^^^^^^^^^^^^
>>                      0x0000000000fc0000 0x0000000000fc0000  RWE    0x10000
>>
>> makedumple uses max_paddr to calculate the number of sections for sparse
>> memory model thus wrong number is obtained based on max_paddr=-1. This
>> error could lead to the failure of copying /proc/kcore for RHEL-8.5 on
>> ppc64le machine [1],
>>     $ uname -r
>>     4.18.0-312.el8.ppc64le
>>     $ makedumpfile /proc/kcore vmcore1
>>     get_mem_section: Could not validate mem_section.
>>     get_mm_sparsemem: Can't get the address of mem_section.
>>
>>     makedumpfile Failed.
>
>IIUC, makedumpfile has NOT been developed to filter /proc/kcore so far,
>except for the --mem-usage option, and this is the first patch for it.
>
>It might be more handy than crash's snap.so extension, so I applied this:
>https://github.com/makedumpfile/makedumpfile/commit/38d921a2ef50ebd36258097553626443ffe27496

Thanks for applying the patch!

>
>But please note that maybe filtering /proc/kcore with makedumpfile (and
>also analyzing the dumpfile with crash) is still not mature enough for
>field or production use.

Thanks for the note!

>
>Thanks,
>Kazu
>
>>
>> Let's check if the phys_start of the segment is a valid physical address
>> to fix this problem.
>>
>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1965267
>>
>> Reported-by: Xiaoying Yan <yiyan at redhat.com>
>> Signed-off-by: Coiby Xu <coxu at redhat.com>
>> ---
>>  elf_info.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/elf_info.c b/elf_info.c
>> index e8affb7..9444847 100644
>> --- a/elf_info.c
>> +++ b/elf_info.c
>> @@ -628,7 +628,7 @@ get_max_paddr(void)
>>
>>  	for (i = 0; i < num_pt_loads; i++) {
>>  		pls = &pt_loads[i];
>> -		if (max_paddr < pls->phys_end)
>> +		if (pls->phys_start != NOT_PADDR  && max_paddr < pls->phys_end)
>>  			max_paddr = pls->phys_end;
>>  	}
>>  	return max_paddr;
>> --
>> 2.31.1
>>
>>
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>

-- 
Best regards,
Coiby