This moves them both to be computed at runtime from a pointer+offset
rather than just a pointer, so that their real address can be entirely
derived from the section they're in.
This means you can replace the whole .vendor_cert section with a new one
with certs that don't have the same size.
With this change, the embedded certificate and dbx lists (vendor_cert,
vendor_cert_size, vendor_dbx, and vendor_dbx_size) wind up being in a
section named .vendor_cert, and so will look something like:
------
fenchurch:~/devel/github.com/shim$ objdump -h shim.efi
shim.efi: file format pei-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .eh_frame 000174a8 0000000000005000 0000000000005000 00000400 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .text 000aa7e1 000000000001d000 000000000001d000 00017a00 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
2 .reloc 0000000a 00000000000c8000 00000000000c8000 000c2200 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .data 00031228 00000000000c9000 00000000000c9000 000c2400 2**5
CONTENTS, ALLOC, LOAD, DATA
4 .vendor_cert 00000375 00000000000fb000 00000000000fb000 000f3800 2**0
CONTENTS, READONLY
5 .dynamic 000000f0 00000000000fc000 00000000000fc000 000f3c00 2**3
CONTENTS, ALLOC, LOAD, DATA
6 .rela 0002afa8 00000000000fd000 00000000000fd000 000f3e00 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
7 .dynsym 0000f1f8 0000000000128000 0000000000128000 0011ee00 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
------
This simplifies a security audit, because it means that different
versions of shim with substantially the same code with different keys
will be more easily comperable, and therefore logic differences may be
more easily identified.
This also means that if there's a trusted build you want to use, you can
remove the certificates, implant new ones, and have it signed, and the
code sections won't change.
Signed-off-by: Peter Jones <pjones@redhat.com>
