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

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

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.

>
> 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.

Thanks,
Tamas

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