Re: [Xen-devel] Booting signed xen.efi through shim

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.09.17 at 16:40, <tamas@xxxxxxxxxxxxx> wrote:
> On Wed, Sep 13, 2017 at 3:21 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 13.09.17 at 07:27, <tamas@xxxxxxxxxxxxx> wrote:
>>>Sections:
>>>Idx Name          Size      VMA               LMA               File off  
>>>Algn
>>>  0 .text         0017a1ba  ffff82d080200000  ffff82d080200000  00001000  
>>> 2**12
>>>                  CONTENTS, ALLOC, LOAD, CODE
>>>  1 .rodata       000826a0  ffff82d080400000  ffff82d080400000  0017c000  
>>> 2**5
>>>                  CONTENTS, ALLOC, LOAD, DATA
>>>  2 .buildid      00000035  ffff82d0804826a0  ffff82d0804826a0  001fe6a0  
>>> 2**2
>>>                  CONTENTS, ALLOC, LOAD, READONLY, DATA
>>>  3 .init         00077df0  ffff82d080600000  ffff82d080600000  001ff000  
>>> 2**12
>>>                  CONTENTS, ALLOC, LOAD, CODE, DATA
>>>  4 .data.re      0000aa40  ffff82d080800000  ffff82d080800000  00277000  
>>> 2**7
>>>                  CONTENTS, ALLOC, LOAD, DATA
>>>  5 .data         000105a8  ffff82d08080b000  ffff82d08080b000  00282000  
>>> 2**12
>>>                  CONTENTS, ALLOC, LOAD, DATA
>>>  6 .bss          00143280  ffff82d080820000  ffff82d080820000  00000000  
>>> 2**4
>>>                  ALLOC, RELOC
>>
>> Objdump is apparently ignoring a section attribute bit here - my
>> own utility properly prints "bss" in addition to "read" (which presumably
>> matches "ALLOC" above, albeit that's a bogus translation apparently
>> applying ELF semantics to COFF). You'll want to check that bit 7 in the
>> section attributes is set. I'm also puzzled by "RELOC", but I do see a
>> matching bit dumped here; not sure why that's being set.
> 
> Looking at it with readpe I get:
> 
> Name:                            .bss
> Virtual Address:                 0x820000
> Physical Address:                0x143280
> Size:                            0 (0 bytes)
> Pointer To Data:                 0
> Relocations:                     0
> Characteristics:                 0xc1000080
>                                  contains uninitialized data
>                                  contains extended relocations
>                                  is readable
>                                  is writable
> 
> So bit 7 is set AFAICT.

Good.

>> It is certainly the case that .bss style sections are expected to have a
>> zero file offset, as there's no data for such sections inside the file (note
>> the missing "CONTENTS" above. So I would conclude that, unless the
>> bss flag really got lost, it's a shim loader bug. Since other people can
>> load xen.efi with the shim, that might be a problem with the particular
>> version you're using.
> 
> Perhaps, I'm using the latest master
> (e22a7b5b772dba6588dd955dc017e572f7e29784) from
> https://github.com/mjg59/shim, the one being linked to on the wiki. If
> there is a known good version, I would be happy to give that a shot
> and see if I can get it working.

I have no idea. What I'd suggest you to try is to zap that stray
"contains extended relocations" flag. I've written down to go hunt
for where it comes from, but I don't have the time to do that right
away.

Jan


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