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Message-ID: <CA+55aFxxUadENxUWU8jZqLnG=hvNA-fKCPQUMCKs2r0yWHc=rA@mail.gmail.com>
Date: Wed, 23 May 2018 16:55:52 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Laura Abbott <labbott@...hat.com>
Cc: Andrew Lutomirski <luto@...nel.org>, mjw@...oraproject.org,
"H.J. Lu" <hjl.tools@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
"the arch/x86 maintainers" <x86@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
nickc@...hat.com, ccoutant@...il.com,
Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCHv3 2/2] x86/vdso: Add build salt to the vDSO
On Wed, May 23, 2018 at 3:53 PM Laura Abbott <labbott@...hat.com> 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
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