Re: [PATCHv3 2/2] x86/vdso: Add build salt to the vDSO

[Linus Torvalds]

On Wed, May 23, 2018 at 3:53 PM Laura Abbott <labbott@xxxxxxxxxx> wrote:

> Actually I remember now why this is necessary: there is not a simple way
> to encode a string into a linker file as it has to be spit out byte
> by byte.

I think you can use the "fill" thing to basically add any random data to a
section.

So you can do something like

        . = ALIGN(16);
        .salt : AT(ADDR(.salt) - LOAD_OFFSET) {
                LONG(0xffaa5500);
                . = ALIGN(16);
        } =0x01234567890abcdef

in the lds file, and you'll get a section that looks like this:

   [torvalds@i7 linux]$ objdump -h vmlinux -j .salt -s

   vmlinux:     file format elf64-x86-64

   Sections:
    Idx Name          Size      VMA               LMA               File off
  Algn
     15 .salt         00000010  ffffffff8432b000  000000000432b000  0352b000
  2**0
                      CONTENTS, ALLOC, LOAD, DATA
    Contents of section .salt:
     ffffffff8432b000 0055aaff 00123456 7890abcd ef001234  .U....4Vx......4

Now whether that is sufficient for your needs, I dunno.

               Linus